I've been doing intermittent fasting (16:8) since 2016 (9 years).
I have a belly and am what you would call "a little chubby". I don't exercise that much (once a week). I drink one black coffee in the morning.
After all these years of IF, net-net I haven't lost any weight, but I find if I stop IF (i.e. I start eating 3 meals a day), I feel sluggish. So in the absence of doing anything else, at least IF keeps my mind sharp.
p.s. the only times I've lost weight is when I've fasted once a week, cut out 50% of all carbs from diet, and starting lifting weights. I lost water weight at first, then plateaued because I gained muscle, then after that muscles did the work of burning excess calories.
I was that way for at least 3 years. Then I decided I loved food too much and added certain carbs back into my diet. These days I just do IF and nothing else, and my weight is stable.
emrahcom
The results are a bit different on my side. I've been doing intermittent fasting (23:1) since 2019 (~6 years). During this period, I did IF (46:2) for a year (one meal every two days).
I have never been overweight in my life but I lost ~10 kg in the first year and my weight has remained stable since then. I haven't measured it, but my body fat percentage is probably around 15%.
By the way I do moderate exercise every days. Walking at very slow speed for 3-4 hours or swimming for an hour. My muscle mass is always increasing, albeit slowly.
HDThoreaun
I do 23:1 and even I think eating every other day is absolutely nuts. Theres no way you are productive the hour before that meal
alexey-salmin
You can try long-distance running. 100km a week allows you to indulge extra 5000-8000k calories.
I also enjoy food and always ate a lot (like 2 meals at lunch), and I was thin all the way up to 30 thanks to fast metabolism I guess. If I didn't start running 5 years ago my choice would be between severe cuts to my diet or obesity.
maccard
I fundamentally think pushing people who want to lose weight into cardio is a mistake. It’s definitely good for you but unless you know how to eat you are going to find yourself over eating very quickly
BigGreenJorts
Been upping my cardio recently for non weight reasons (just want to improve overall endurance for certain sports and heart health) man have I been feeling this. It's crazy how much just a little bit of extra cardio revs up my appetite. It's been about a week and I'm still figuring out how to manage it.
rkomorn
100km/week isn't just "cardio", though. It's a whole lot of it.
I agree that "a little cardio" (eg 30-45 minutes 2-3 times a week) can definitely be counterproductive.
I have to mix in a lot of weight lifting to actually lose weight and offset the appetite creep.
alexey-salmin
I don't know, it's not an easy path but it works more often than fasting for people around me.
Or you're suggesting exercise but of different kind?
maccard
It’s way easier to avoid eating the calories than it is to exercise them off in practice. For most people exercise will cause them to feel hungry, and to eat. I’d you don’t know how much to eat you’ll end up having the wrong effect and gaining weight.
It’s also way easier to just not eat the calories in the first place. A bag of potato chips or a tbsp of nut butter on a rice cake is roughly the equivalent of 15 minutes of running.
Everyone should exercise and move but if it’s for weight loss diet is the way
I think he's saying you'll compensate by eating more.
Walking might be a better choice but no matter what you do you still need to control the intake of calories.
maccard
Yeah - walking solidly for an hour is going to max out at about 250 calories (unless you start hill walking or adding extra weight). A latte (not even a Starbucks-y sugary one) is about the same amount of calories.
You should walk. It’s really good for you. But skipping the coffee break at the end will have more of an impact on your weight than the walk itself.
theshrike79
People (try to) run too fast by default. I blame movies and media.
The best way to "run" is actually kind of a springy hop at about a brisk walking speed. This is what the actual pros do outside of competitions to build endurance.
AstroBen
Getting into cycling actually has me about to stop intermittent fasting. I go out and can burn 1200 calories in a few hours and that's hard to make up with an 8-hour eating window unless I want to start eating a bunch of junk food. Not trying to lose any more weight
rkomorn
Cycling 10-12 hours a week (and going pretty hard at it thanks to the many hills in the Bay Area) let me eat just about everything I wanted while still losing weight.
If you have the time and enjoy it, there's no better way to be able to stuff yourself silly.
zihotki
You can't outrun a bad diet
pointlessone
100 km is like 12 hours. Probably much more if you’re just starting. 2h/day is quite a commitment.
"Try running 50+ miles a week in order to eat more" is an insane suggestion.
alexey-salmin
Why? Not that it's universally applicable, but if it works for you then why not.
taeric
Did you keep up the weight lifting?
testing22321
What are you eating?
Soda? Chocolate? Sugar? Ice cream?
You must be eating something extremely calorie dense to be maintaining weight.
keiferski
In my experience IF is better thought of as a way to break bad eating habits, not as a direct way to lose weight. Merely eating the same amount of food but in a certain time frame (which is what a lot of people end up doing) doesn’t accomplish much in terms of weight loss.
But I have found it successful in breaking bad habits, which results in weight loss indirectly.
For example, I had a bad habit of eating a large breakfast 1-2 hours within waking up. I was never really that hungry, but it was just something I did out of habit. Doing an IF routine made me realize that I’m not actually that hungry in the morning and can get by until 10-11am on just a coffee with milk.
calmbonsai
I'd go further and say adopting any sort of diet regimen is useful for identifying and correcting bad eating habits. Even if the diet ends up being a temporary discipline.
Having any high duty-cycle behavior go from un-tracked to tracked and from (largely) unconscious habitual practice to conscious practice can be a real eye opener.
somenameforme
I'd agree and generalize that intermittent fasting is a great way to remind yourself that that feeling in your stomach when you get hungry doesn't mean you need to eat now. In fact, there's no real rush whatsoever. The first time I did a 24 hour fast, it was brutal and I treated myself to a feast at the end which I rapidly gobbled down.
After doing intermittent fasting for a few years, I have accidentally fasted for 24+ hours multiple times. And after you do it for a while, it makes it clear that this whole modern thing of 3 meals a day, let alone with snacking, is really just weird.
throwaway290
Coffee with milk is not breaking IF?
keiferski
I didn’t elaborate enough in my comment. Basically I mean that I stopped eating breakfast with IF and then gradually realized a coffee with milk was enough to serve as a replacement.
The point being that rigidly sticking to IF rules is less useful than just using it as a way to reset your eating habits. (At least in my experience.)
paulpauper
calories= breaking the fast
Almondsetat
What all these diets are desperately trying to do is psychologically manipulate you into eating less by playing with your sense of fullness. For weight loss, thermodynamics cannot be beaten: eating at different times and in a different order does not matter.
svnt
This is trivially shown to be false.
Imagine a system with a background/quiescent energy consumption of 1000kCal/day.
Imagine that same system can buffer up to 500kCal for up to 24 hours store excess energy in circulation.
Imagine it converts excess energy to stored energy at an efficiency of 50%.
Assume activity correlates with marginal energy consumption but also increases in the presence of excess energy.
A system such as the one described would have very different behaviors during alternate day fasting (0kCal for 24hrs, 5000kCal for 24hrs) than consuming 2500kCal daily.
The human body is more complex than the system I just described, but it is a useful model to consider for this context.
greysphere
Real world efficiency factors are in the 90s and basal rates aren't constant. The model you're proposing is too artificial to draw conclusions about fasting over a short timeframe.
svnt
Then please provide a more accurate one that supports the opposite and simplistic conclusion that it doesn't matter when you eat what calories.
red_trumpet
So, the excess energy in your model is just excreted? Does that also happen in the human body?
wouldbecouldbe
Yes. On the other spectrum, the body becomes more efficient when moving a lot.
rolisz
Unfortunately calories out is a function of calories in.
You eat less calories, your body might start consuming less calories.
Also, there are two different pathways for using glucose in the body: aerobic and anaerobic. The aerobic one produces 15x more ATP (cellular level energy) than the anaerobic one. The anaerobic one wastes more as heat. So if for some reason you're in the second one, even though you ingest the same amount of calories, the amount of energy you have usable is much less.
So yeah, calories in calories out is true, but it's not really helpful.
rkomorn
> So if for some reason you're in the second one, even though you ingest the same amount of calories, the amount of energy you have usable is much less.
This is technically true but not particularly relevant.
It's quite difficult to be in only anaerobic effort, though (and I'd say pretty ill advised since that basically means stuff like all out sprinting without warmup or cooldown).
Higher intensity effort burns more calories than lower intensity (eg [1]). It's just harder to sustain.
Thiamine deficiency can cause anaerobic usage for example, without having to do intense exercise. Severe insulin resistance is another one. Cancer cells predominantly use anaerobic burning (Warburg effect). Various blocks at mitochondrial level, such as carbon monoxide, can also drive metabolism towards anaerobic pathways.
ourmandave
Confirmed by the study of populations of 34 countries.
Food — not lack of exercise — fuels obesity, study finds
This is an entirely useless thing to say. Your body can make choices, based on what and when and how you eat, that you can't control with your psychology.
Your body can raise or lower its temperature. It can put energy towards cell repair or cell reproduction. It can store energy as fat, or signal to burn fat, or build muscle or catabolize muscle.
flyinglizard
You’re assuming the body is a constant machine that metabolizes at a fixed rate but that can’t be true.
tekla
Until the human body becomes capable of creating energy out of nothing, this is irrelevant
alexey-salmin
It's not. Human body can't create energy out of nothing, but it can vary the consumption of energy in a wide range which is very similar in terms of externally observable effects.
It's a common story when people start to eat 20% less, continue the same lifestyle and lose exactly zero weight as the result. Their body didn't create 20% of energy out of nothing but it just started to waste less energy as body heat.
maccard
20%? That’s 4-500 calories a day less. Have you hit any links to this as it’s a pretty wild claim
tekla
Irrelevant, energy out > energy in, you lose weight
It can use different amounts of energy depending on different stimulus. Things like fidgeting and body temperature can make a pretty decent difference
anon84873628
Just to add some color for folks, this is referred to as NEAT in the literature: Non-Exercise Activity and Thermogenesis.
When caloric intake is reduced, the body can decrease this type of expenditure without the person even realizing it.
objektif
Very bad take. What if our bodies adjusts the burn rate based on when we eat when we exercise? if that is true you can potentially eat more and lose more weight.
tekla
Irrelevant, energy out > energy in, you lose weight
It’s not just different times though. When doing intermittent fasting you easily ingest less calories overall, skipping a meal doesn’t mean you’ll eat twice as much for the next meal.
I don’t understand what’s "desperate" about IF, it’s just an easy way (for some people) to lower their calories intake. It has other benefits and some caveats but it’s one way to get healthier.
827a
Calories in / Calories out might be broadly accurate, but reality is a lot more complicated than that. People are really bad at tracking how many calories they take in. Its impossible to measure how many calories you're actually exerting with exercise. Its even more impossible to measure how many calories you pee, poop, perspire, breathe, and radiate out. Microvariations across your current body state, body temperature, and even the time of day can influence how efficient your gut is at absorbing incoming energy.
Some people operate with a goal of a caloric deficit of even something as small as e.g. 200kcal. But because all these things are impossible to measure accurately, a difference of just 10% beyond a daily BMR of 2000kcal isn't just a possibility; its the norm. You run for an hour; what if that burns an extra 50kcal that your Apple Watch did not account for? You eat a slice of bread which advertises it contains 80kcal; but it actually contains 100kcal [1]? You sleep poorly, which causes some mild systemic inflammation the next day, which raises your body temperature?
The really cool part is you don’t have to accurately track how many calories go in and out. The proof is in the pudding.
If you had a car with a broken gas gauge you would just pump until it overflowed… same idea here.
Over a month or so if your weight is stable then you are putting in as many calories as you burn. If you’re gaining weight, you’re consuming more, and if you’re losing weight, you’re consuming less.
Adjust accordingly.
827a
Sure, but no one can actually do that accurately, for the aforementioned reasons. "I'm gaining weight; I should eat less": How do you structure that in a way that's actually actionable and drive results? Just a general sense that "eh I should eat less"? No one eats consistently enough, or exerts energy consistently enough, to actually make vibe-structuring cal-in/cal-out possible. You might think "I should work out more, that's more calories out" -> but ask literally any runner about how running affects their appetite and you'll realize quickly how wrong that is.
Hence: Why diets exist. That is the structure. There are good ones and bad ones.
Keto, for example, can work for weight loss not because there's anything particularly interesting about the way your body absorbs carbs versus protein and fat (there are differences, but its not the biggest reason why it can work). It can work for some people because typical protein and fat food sources are less calorically dense (by volume and weight) than carb sources. You may feel full faster; so you may naturally eat fewer calories.
Similarly: IF can work for some people because most people cannot physically eat enough to consume massive calorie counts if they time-restrict the hours they're allowed to eat. It also seems to come with some well-studied metabolic effects.
You don't have to accurately track inflows and outflows, but vibe-structuring your consumption and exertion habits based on outcomes is a privilege that, sure, some people have, but is not a panacea for every body and mind. Broadly, the people who need to make change who do this will not see the change they wanted.
testing22321
> No one eats consistently enough, or exerts energy consistently enough, to actually make vibe-structuring cal-in/cal-out possible
Of course we do!
You’re thinking of this the wrong way. The goal isn’t “eat less” as you said, it’s “consume less calories (energy)”
On any given month if you gain weight or maintain when you want to lose, then you need to consume less energy next month. For 99% of people, that means reduce sofa, reduce sugar, reduce fat (all the energy dense stuff)
Feeling hungry? Drink massive glasses of water and eat literally all the vegetables you physically can get in. I have whole carrots for snacks most days. Cauliflower too. Cucumber is great. Frozen peas on a hot day. All of it, as much as you can eat.
You're overestimating the difficulty here. You don't really need to wait a month either. There's plenty of variance on a day by day basis, but you can still generally see whether the number is trending up or down. And most people tend to cycle through the same foods, so portion control isn't particularly hard.
For instance this is something every single person who's into body building does, because you want to be in a slight caloric surplus when bulking, and then you want to get back into a slight calorific deficit when cutting.
calmbonsai
Oh my NO! Just...no.
It turns out the body processes different calories very differently depending on a variety of factors including: baseline genetics, time of day, menstrual cycle, prior fasting, current mineral excess/debt, gut flora/fauna biome, and the composition of previously consumed food still remaining the digestive track.
BennyH26
In our medical practice, we would use intermittent fasting as part of a comprehensive medical plan to increase longevity. There are studies which demonstrate this is beneficial, at least in Macaque monkeys. Weight loss was just a nice side effect.
anon84873628
As Mike Israetel puts it, you don't want your body swimming in nutrients all day every day.
Whether it's IF, deficit cycles, periodic deep fast -- they all seem to have the same effect, which is just to give the body a break for a bit.
sublinear
I lost 130 pounds over the course of 2 years in my late 20s by skipping lunch every other day and entirely skipping breakfast. I also started tracking my calories and macros.
I don't know what to call that, but it worked and it changed my relationship with food forever (in a good way). I have since kept the weight off and switched back to eating 3 meals a day with a better understanding of how much and of what to eat.
Eat a lot more protein and way less carbs. Most meats already have the right balance of fat included, so avoid adding more. Fill up on fibrous vegetables since they don't really count towards calories and help digest all the meat you'll be eating. Drink plenty of water, sleep well, and at least hit your daily steps and heart rate targets if you're not huge on exercise. Building muscle is a good idea, but I'm lucky I've never had a problem with that and just needed to lose the body fat.
I'm now in my mid 30s and have a clean bill of health. When I was heavier I was prediabetic and my resting heart rate was 85. Now it's about 65 and blood sugar is good and doesn't spike or stay elevated all day anymore. It's good to get this stuff on track when you're still youngish.
Oh also I stopped the intermittent fasting because it was messing with my blood sugar. That was why I wrote all this and it's my argument against it.
porridgeraisin
Practical advice for people who do normal 80/20 healthy/unhealthy stuff and don't wanna think:
Now and then like twice a month, skip 2/3 meals in the day. If hard, have light juices/even fruits. Think of it as giving your digestive system "rest". Don't do it when otherwise sick.
It will make you generally healthier, no drastic changes. Those require drastic measures which differ person to person.
strken
I'm not sure that a reduction in body weight tells us all the relevant information. One of the possible downsides of fasting is loss of lean body mass, generally meaning muscle. This is a problem for older people in particular because it's harder to keep muscle as you age and because muscle protects from falls, frailty, etc.
testing22321
If a person is obese or morbidly obese, losing weight is the number one priority to increase overall health, lifespan, quality of life, etc etc.
Losing a bit of lean muscle mass along the way is not important compared to the huge health gains of losing the weight.
strken
I agree that losing body fat is the number one priority, but I wish the research would focus on that rather than the number on the scale. Losing a bit of lean muscle mass along the way is important for its own sake, and also because it's a confounding variable for what I actually want to know, which is how much fat (not weight) a person lost.
testing22321
Why does it matter?
When it comes to long term health outcomes, losing weight is the only thing that matters.
AstroBen
I don't think this is specific to fasting?
You need to be getting enough protein + strength training to maintain muscle in a caloric deficit
Someone1234
Weight loss is linked with some loss of lean body mass, regardless of the method used. Intermittent fasting has been shown to match any other calorie deficit in terms of lean body mass loss, rather than more as you're implying.
Regardless of how you lose weight the advice is and remains:
> Eat a minimum of 0.36 grams of protein per day, per pound of LEAN* body weight. Increasing to 0.5-0.7 grams of protein per day, per pound of LEAN* body weight for older adults or when undergoing weight loss.
*LEAN is a vital detail for overweight people, they commonly miscalculate protein requirements due to this. The easiest way for overweight people to determine their requirement, is just find an "ideal body weight calculator" online, enter height and gender, and then multiply THAT figure by 0.5-0.7.
For example a man who is 6' tall and 400 lbs should eat 62 grams of protein per day MINIMUM, but during weight loss 86-120 grams of protein per day. It is common, unfortunately, to read online people in this situation miscalculate this to 280(!) grams of protein per day which is incorrect and harms their weight-loss goals.
funcDropShadow
Do you have source for this? Because as you write I've always read to derive protein intake from the overall weight. That would indeed be a very important distance.
Someone1234
Yep, it is often repeated bad advice that was originally aimed at healthy weight adults and athletes and then misunderstood by people attempting to lose body fat. It is incorrectly repeated on hundreds of exercise sites and articles. Cite:
> Protein intake should range between 1.0-1.5 grams/kg of adjusted body weight. To calculate adjusted body weight, first calculate excess weight: Excess weight = current weight — ideal body weight (IBW). Adjusted body weight = IBW + 0.25 of excess body weight. This amount generally accounts for 20% to 30% of total caloric intake.
So a slightly more complex way of calculating roughly the same thing. I'd argue that for most people getting your ideal weight is a good enough approximation, and that using your overweight/obese body fat in your protein calculation is wrong by a lot no matter which calculation you use.
I diet, on and off. Keeping fat free weight as the highest priority (I don’t want to loose hard earned muscle)!
I’ve tried all types of diets. For me, the most important for me is to save the biggest meal for late in the day. I can easily go hungry a couple of hours during the day if I know there is a filling meal coming.
I suspect IF works in a similar way.
sebazzz
> For me, the most important for me is to save the biggest meal for late in the day.
Wouldn't the big meal be stored as fat during sleeping?
knowitnone2
I did intermittent fasting. I think this conditioned me to being in the hunger state and to ignore hunger. Along with exercise and portion control, I did lose 20 pounds. I could have gone further but I became lacking in certain nutrients and a doctor told me to stop.
bonvoiay
It surprises me how often the basic physiology still gets overlooked.
Hunger is driven by hormonal signals designed to defend a set point. Even if you consciously fast for most of the day, your brain will push you to make up the difference once you start eating. When it comes to fat loss, it still boils down to maintaining a caloric deficit — timing alone won’t keep your appetite in check for long. We’ve known this for years.
IF may have other potential benefits — better insulin sensitivity, longevity, or improved adherence for some people (since avoiding food most of the day can be psychologically easier) — but none of that is “new” anymore.
mrbonner
I’m curious whether taking the oral form of Ozempic at a lower dose could have effects similar to intermittent fasting, given that it may lead to skipping a meal as well.
kaycebasques
Microdosing ozempic
gorfian_robot
Diet Coke now with GLPs?
garrickvanburen
After briefly looking into it, my assumption is intermittent fasting works great for people that are eating throughout the entirety of the day.
abracadaniel
I’ve often wondered about this. If you have a sugary drink, would it be better to drink it in one sitting or sip it throughout the day.
lkrubner
I have read that before the Industrial Revolution, most people faced famine for about 10% of their lives. And while, historically, that would have probably been concentrated into a few bad years during their lifetime (months of starvation, during a few bad years), if we were to generalize that and make it a rule, it would work out to 3 days a month.
There is some evidence that there are health benefits that are specific to the fasting mode. This has mostly been studied in the context of chemotherapy, where fasting can protect against some of the side-effects of chemotherapy:
Most of this has only been studied in animals, not humans, but in animals the results were clear:
"Fasting before chemotherapy (CT) was shown to protect healthy cells from treatment toxicity by reducing the expression of some oncogenes, such as RAS and the AKT signaling pathway [2]. This reduction is mediated by the decrease of circulating insulin-like growth factor 1 (IGF-1) and glucose. In addition, starvation and calorie restriction activate other oncogenes in cancer cells, induce autophagy, and decrease cellular growth rates while increasing sensitivity to antimitotic drugs [2]."
If we assume that we have been shaped by millions of years of frequent famine, then our evolution has been shaped by famine. It is possible that our immune system simply makes the assumption that we will soon face famine, and therefore some important tasks, such as extreme autophagy, are normally postponed till the famine arrives. However, in the modern era the famine never arrives, and so we may have to induce it by artificial means.
I have experimented with very long fasts. My longest fast ever was in September of 2015 when I managed to go 12 straight days on nothing but water.
Obviously, any health benefits from that incident might have been psychosomatic, since I was expecting health benefits. But all the same, I did find some of the health benefits to be shocking and completely unexpected. Since at least 1995, and possibly 1990, I had a mole on my skin on my left arm. I wasn't worried about it, so I simply ignored it. I had it on my arm at least 20 years, maybe 25 years. I recall one morning in November of 2015 when I was in my kitchen, making breakfast, and I reached over to pour myself some coffee, and of course my arm was in my field of vision, and after a moment of thinking something was different, it occurred to me that the mole was gone. It had been there at least 20 years, and then it disappeared, at some point during the weeks after I had done the 12 day fast. I don't know when it disappeared, it just slowly faded away at some point between September and November. There was no remaining sign of it on my arm.
Again, that might have been purely psychosomatic, but it was interesting.
ellen364
Admittedly a minor point of interest, but the last famine in England happened in 1623 and was local to an area called Westmorland [0]. That was 150 years before the Industrial Revolution, so the 10% figure might not be very reliable.
England was the first nation to escape from famine. A national market began to take shape shortly after the civil war, and the national market transformed traditional famine into a question of high prices. Jethro Tull began his experiments in 1701, and Charles Townsend began taking notes about fertilizer shortly afterwards, and when the public became aware of their work, the Agricultural Revolution began, and then, shortly afterwards, the Industrial Revolution. But obviously, most of the world continued to experience famine into the 1900s.
alchemist1e9
Are you religious or spiritual in any way and if so was there a connection to that and your twelve days water fast?
1024core
Every study ends with something along the lines of:
Longer duration trials are needed to further substantiate these findings.
pdxandi
I read that as needing funding. Somebody has to pay for the research. In order to get it funded, you have to show your research has a basis. My interpretation anyway.
mrandish
N=1 but in 2017 I lost over 100 pounds in 8 months by changing to a keto + IF diet and I've kept it off. I lost 10 pounds in 10 days and 20 pounds the first month. At around six weeks I became 'fat-adapted', a long-term metabolic transition to primarily burning fat instead of carbs (glucose) for energy. I didn't start with IF but at around that point I sort of fell into intermittent fasting because it just felt right. I'd heard about IF but never had it as a goal because it seemed impossible since I'd been hungry my whole life. But limiting carbs with keto controlled my blood sugar to the extent I was almost never hungry which made IF trivially easy. So if you're trying IF and struggling with hunger pangs, try managing blood sugar by reducing carb intake.
The combination of Keto+IF worked so well for me, for a while my calorie tracking switched from the usual preventing eating too many calories to ensuring I was getting enough, which was certainly never on my bingo card. After a lifetime of being a slave to hunger it was liberating to suddenly feel effortlessly in control of diet and my relationship with food changed completely. Then at around 90 days my palate shifted, meaning I even lost my taste for carbie foods. If I tried a small bite of something carb-laden that I'd loved my whole life, it didn't even taste particularly good to me anymore. I also became hyper-sensitive to sugar. Sugar-soaked foods just taste poisonously over-sweetened (which they kind of are). A slice of apple now tastes as sweet as I'd ever want, like a dessert that has extra sugar-added.
In the 8th month I reached below my ideal 'dream' weight and even saw abs appear for the first time in my life! I transitioned to maintenance mode but stayed keto because being in a blood sugar controlled state felt so amazing and not just physically but also mentally and emotionally. At around a year I went from strict keto to low carb for life which I still am 8 years later. When I started that was unimaginable. I saw keto as an onerous regimen that I'd endure if it worked and stop the second I wasn't overweight. But during the journey my metabolism, palate and food preferences changed so dramatically, I was basically a different person when I arrived. Those first few months when I was rigorously tracking every calorie in an app and managing intake with measuring cups and a kitchen scale felt like a burden but were actually invaluable skill-building. After a few months all that process became automatic so I didn't need to constantly track and by six months I got to the point where I don't even think about it consciously. That early rigor helped me get so in sync with my body and able to sense where my metabolism is in its natural cycles that now I just eat when necessary and convenient for my schedule. This often ends up being IF but it's not intentional on my part, which makes me think maybe IF patterns evolved in the hunter/gatherer era as part of our natural biological rhythms. Due to habit and carb-laden factory foods I'd never been able to access those rhythms until I made the conscious effort to break the patterns I'd been raised in.
xianwen
Hi. Could you maybe share the keto and the low carb diets that you use(d)?
mrandish
Keto is different in that there's not really a "keto" diet, just the principle of limiting carb intake to under 20 grams/day. "Low Carb" isn't a well-defined term but most people take it to mean under 100g of carbs/day. Thus, there's a huge variety of ways to do keto depending on your lifestyle and food preferences. I did a lot eggs, meats and cheese because I like those.
I suggest you read the FAQ of the Reddit keto forum: https://www.reddit.com/r/keto/wiki/faq. I recently posted my personal "Keys to Keto Success" learned during my 8 month weight loss 8 years ago: https://www.hackerneue.com/item?id=44685689 which includes some effective hacks I discovered. The biggest thing is to do keto rigorously. It's different than most any other diet because it's not just about reducing calories. The power of keto is 100% in cutting carbs, which is why I advise "Cheat all you want on calories but never (ever) on carbs".
For me, cutting calories on any diet was always difficult, painful and exhausting. Keto worked because I only focused on cutting carbs. Once I got my blood sugar under control by limiting carbs, my raging hunger just evaporated and the calories pretty much took care of themselves. The change was dramatic. After the first month I was no longer tracking calories to stop over-eating but instead to ensure I was getting enough :-). During the second month there was a point where I was slightly concerned I might be losing weight too fast because I was never hungry, which was certainly never something I'd imagined would be a problem for me. Of course, that's easily addressed by increasing calories a bit.
There's just one thing to watch out for as you do keto. On keto you're able to eat a lot of fats which are very filling (and delicious). This is wonderful but it's only possible because having almost no carbs puts you in a ketogenic state where instead of burning glucose (carbs) for energy as you do now, your body burns those fats for energy instead of storing them (weight gain). So, unlike a normal calorie-reduction diet, where you can slip one day and just get back on the wagon the next day, cheating on carbs during keto will convert all that delicious fat you're eating into not only pounds of weight but potentially into all the bad stored fat related things like vascular plaque etc. So, basically, keto is the one diet where cheating doesn't just "delay your weight loss another day", it changes from magically protecting you from the negative effects of eating huge amounts of fat to actively making it much worse. Eating all that luscious fat thinking you're protected by Keto but then regularly cheating on carbs "just a little" (as many do on other diets), is pretty much the worst diet imaginable. You'll turbo-charge weight gain AND all the negative effects of excess fat consumption (cholesterol, lipids, A1C, etc). Theoretically, aggressively eating keto-levels of fat but NOT being in a ketogenic state to burn it off could, given time, make you pre-diabetic and your lipid blood panels will freak your doctor out.
So, IMHO, keto is wonderful but there's just one unbreakable rule. You really, really can't cheat on keto (even a little). When I first understood this I was a little concerned but as I researched more it made complete sense. Keto isn't magic. With all these benefits of easy weight loss and healthy metabolism of course there's a potential downside to avoid. Now you know what it is - so go in with eyes wide open. For me, the stringent, "can't cheat, ever" (on carbs) aspect of keto was actually a psychological benefit. It made it 100% binary and thus easy to fully commit. I'm either really doing this or I shouldn't bother. Putting tangible health consequences on regularly "slipping just a little" actually helped me stick with keto rigorously during the first few weeks of transition and habit change (which is really the only hard part, after 30 days keto gets much easier). But you may be different, so you just need to decide if you can really commit 100% for the first ten days. If you manage that, then set your goal to finish the month. The rest really is all downhill from there. If you're as overweight as I was, after the first month of strict keto your weight loss will be so obvious people will definitely notice. In the second month, my admin told me people at the office were asking her if I was "okay", like they were worried I had cancer or was on chemo :-). So I started sharing a little more widely that I'd changed my eating habits. At least nowadays most people have heard of keto.
xianwen
Thank you very much for your detailed reply!
One thing that I'm concerned with, is longevity when a person is on keto. Do you share this concern? Do you know any reliable data source on keto diet's impact on longevity?
mrandish
> Do you share this concern?
I have no concern because there's nothing about a low carb diet that restricts any essential nutrients. On evolutionary time scales, consuming a significant amount of carbs is a recent and unprecedented change to human diets. There are three types of macro-nutrients: protein, fat and carbs. For most of history our hunter/gatherer ancestors ate far more protein and fat than carbs, which is why they were in a ketogenic state most of the time. It's only in the last hundred years in Western democracies that carbs have become overwhelmingly dominant in human diets. In terms of long-term dietary impact, highly-processed manufactured foods and intensive factory farming (which are mostly carbs) are the massive uncontrolled experiment on the broad population that's worth being concerned about. That's the new thing for which there's no long-term data whereas keto has tens of thousands of years of proven success in humans. Going from the Standard American Diet to keto is opting out of the uncontrolled experiment and returning to what we know works. Chronic obesity and Type II diabetes are diseases of diet and they weren't common in humans until the last hundred years.
As for my personal health and longevity, keto has certainly added at least a decade to my life because before keto I was significantly overweight and had been diagnosed with pre-diabetes, high blood pressure, high triglycerides and bad HDL/LDL. I also had chronic sleep apnea as well as IBS/GERDS. I was on five prescribed medications to treat these issues. By the end of the first year on keto those serious health problems had completely resolved and I was off all five medications. To be clear, keto itself isn't some miracle cure. These problems were caused by my obesity and unhealthy diet. Keto helped me not be obese and to eat a healthier diet richer in nutrients and with far fewer manufactured and processed foods. My previous diet was making me sick.
The takeaway here is that if you do “alternate day fasting”, that is you eat normally on one day then do not eat all the next, you will lose weight.
I can’t believe that losing 3.5 days of caloric intake would result in weight loss. In other news, water is wet.
m4r71n
Alternate day fasting normally means you eat up to 500 calories on your fasting day, but then eat more than usual on normal days. So on average if you eat 500 one day and 2500 another, that is no different than eating a restricted diet of 1500 every day. The finding here is that the former results in slightly more weight loss than the latter. That restrictions in calorie intake will result in weight loss is a given.
scns
> eating a restricted diet of 1500
Keeping this up is hard, many fail. Alternating normal eating with IF days is easier to do.
layer8
No, the takeaway is that it results in more weight loss than intermittent fasting and whole-day fasting.
fred_is_fred
Or if you just ate 50% less calories 7 days a week perhaps.
treetalker
My understanding is that, yes, the weight loss results end up being similar — but that the story is not so simple (or linear) because "true" fasting activates certain metabolic pathways (e.g., mTOR) that mere calorie reduction does not, and that those pathways have different effects, such as autophagy and others that increase lifespan in different ways.
physicles
As other commenters and TFA have pointed out, that “just” is doing a lot of heavy lifting
I have a belly and am what you would call "a little chubby". I don't exercise that much (once a week). I drink one black coffee in the morning.
After all these years of IF, net-net I haven't lost any weight, but I find if I stop IF (i.e. I start eating 3 meals a day), I feel sluggish. So in the absence of doing anything else, at least IF keeps my mind sharp.
p.s. the only times I've lost weight is when I've fasted once a week, cut out 50% of all carbs from diet, and starting lifting weights. I lost water weight at first, then plateaued because I gained muscle, then after that muscles did the work of burning excess calories.
I was that way for at least 3 years. Then I decided I loved food too much and added certain carbs back into my diet. These days I just do IF and nothing else, and my weight is stable.
I have never been overweight in my life but I lost ~10 kg in the first year and my weight has remained stable since then. I haven't measured it, but my body fat percentage is probably around 15%.
By the way I do moderate exercise every days. Walking at very slow speed for 3-4 hours or swimming for an hour. My muscle mass is always increasing, albeit slowly.
I also enjoy food and always ate a lot (like 2 meals at lunch), and I was thin all the way up to 30 thanks to fast metabolism I guess. If I didn't start running 5 years ago my choice would be between severe cuts to my diet or obesity.
I agree that "a little cardio" (eg 30-45 minutes 2-3 times a week) can definitely be counterproductive.
I have to mix in a lot of weight lifting to actually lose weight and offset the appetite creep.
Or you're suggesting exercise but of different kind?
It’s also way easier to just not eat the calories in the first place. A bag of potato chips or a tbsp of nut butter on a rice cake is roughly the equivalent of 15 minutes of running.
Everyone should exercise and move but if it’s for weight loss diet is the way
Walking might be a better choice but no matter what you do you still need to control the intake of calories.
You should walk. It’s really good for you. But skipping the coffee break at the end will have more of an impact on your weight than the walk itself.
The best way to "run" is actually kind of a springy hop at about a brisk walking speed. This is what the actual pros do outside of competitions to build endurance.
If you have the time and enjoy it, there's no better way to be able to stuff yourself silly.
Soda? Chocolate? Sugar? Ice cream?
You must be eating something extremely calorie dense to be maintaining weight.
But I have found it successful in breaking bad habits, which results in weight loss indirectly.
For example, I had a bad habit of eating a large breakfast 1-2 hours within waking up. I was never really that hungry, but it was just something I did out of habit. Doing an IF routine made me realize that I’m not actually that hungry in the morning and can get by until 10-11am on just a coffee with milk.
Having any high duty-cycle behavior go from un-tracked to tracked and from (largely) unconscious habitual practice to conscious practice can be a real eye opener.
After doing intermittent fasting for a few years, I have accidentally fasted for 24+ hours multiple times. And after you do it for a while, it makes it clear that this whole modern thing of 3 meals a day, let alone with snacking, is really just weird.
The point being that rigidly sticking to IF rules is less useful than just using it as a way to reset your eating habits. (At least in my experience.)
Imagine a system with a background/quiescent energy consumption of 1000kCal/day.
Imagine that same system can buffer up to 500kCal for up to 24 hours store excess energy in circulation.
Imagine it converts excess energy to stored energy at an efficiency of 50%.
Assume activity correlates with marginal energy consumption but also increases in the presence of excess energy.
A system such as the one described would have very different behaviors during alternate day fasting (0kCal for 24hrs, 5000kCal for 24hrs) than consuming 2500kCal daily.
The human body is more complex than the system I just described, but it is a useful model to consider for this context.
You eat less calories, your body might start consuming less calories.
Also, there are two different pathways for using glucose in the body: aerobic and anaerobic. The aerobic one produces 15x more ATP (cellular level energy) than the anaerobic one. The anaerobic one wastes more as heat. So if for some reason you're in the second one, even though you ingest the same amount of calories, the amount of energy you have usable is much less.
So yeah, calories in calories out is true, but it's not really helpful.
This is technically true but not particularly relevant.
It's quite difficult to be in only anaerobic effort, though (and I'd say pretty ill advised since that basically means stuff like all out sprinting without warmup or cooldown).
Higher intensity effort burns more calories than lower intensity (eg [1]). It's just harder to sustain.
1- https://www.webmd.com/fitness-exercise/what-to-know-heart-ra... )
Food — not lack of exercise — fuels obesity, study finds
https://www.npr.org/2025/07/24/nx-s1-5477662/diet-exercise-o...
Your body can raise or lower its temperature. It can put energy towards cell repair or cell reproduction. It can store energy as fat, or signal to burn fat, or build muscle or catabolize muscle.
It's a common story when people start to eat 20% less, continue the same lifestyle and lose exactly zero weight as the result. Their body didn't create 20% of energy out of nothing but it just started to waste less energy as body heat.
When caloric intake is reduced, the body can decrease this type of expenditure without the person even realizing it.
I don’t understand what’s "desperate" about IF, it’s just an easy way (for some people) to lower their calories intake. It has other benefits and some caveats but it’s one way to get healthier.
Some people operate with a goal of a caloric deficit of even something as small as e.g. 200kcal. But because all these things are impossible to measure accurately, a difference of just 10% beyond a daily BMR of 2000kcal isn't just a possibility; its the norm. You run for an hour; what if that burns an extra 50kcal that your Apple Watch did not account for? You eat a slice of bread which advertises it contains 80kcal; but it actually contains 100kcal [1]? You sleep poorly, which causes some mild systemic inflammation the next day, which raises your body temperature?
[1] https://health.clevelandclinic.org/are-calorie-counts-accura...
If you had a car with a broken gas gauge you would just pump until it overflowed… same idea here.
Over a month or so if your weight is stable then you are putting in as many calories as you burn. If you’re gaining weight, you’re consuming more, and if you’re losing weight, you’re consuming less.
Adjust accordingly.
Hence: Why diets exist. That is the structure. There are good ones and bad ones.
Keto, for example, can work for weight loss not because there's anything particularly interesting about the way your body absorbs carbs versus protein and fat (there are differences, but its not the biggest reason why it can work). It can work for some people because typical protein and fat food sources are less calorically dense (by volume and weight) than carb sources. You may feel full faster; so you may naturally eat fewer calories.
Similarly: IF can work for some people because most people cannot physically eat enough to consume massive calorie counts if they time-restrict the hours they're allowed to eat. It also seems to come with some well-studied metabolic effects.
You don't have to accurately track inflows and outflows, but vibe-structuring your consumption and exertion habits based on outcomes is a privilege that, sure, some people have, but is not a panacea for every body and mind. Broadly, the people who need to make change who do this will not see the change they wanted.
Of course we do!
You’re thinking of this the wrong way. The goal isn’t “eat less” as you said, it’s “consume less calories (energy)”
On any given month if you gain weight or maintain when you want to lose, then you need to consume less energy next month. For 99% of people, that means reduce sofa, reduce sugar, reduce fat (all the energy dense stuff)
Feeling hungry? Drink massive glasses of water and eat literally all the vegetables you physically can get in. I have whole carrots for snacks most days. Cauliflower too. Cucumber is great. Frozen peas on a hot day. All of it, as much as you can eat.
For instance this is something every single person who's into body building does, because you want to be in a slight caloric surplus when bulking, and then you want to get back into a slight calorific deficit when cutting.
It turns out the body processes different calories very differently depending on a variety of factors including: baseline genetics, time of day, menstrual cycle, prior fasting, current mineral excess/debt, gut flora/fauna biome, and the composition of previously consumed food still remaining the digestive track.
Whether it's IF, deficit cycles, periodic deep fast -- they all seem to have the same effect, which is just to give the body a break for a bit.
I don't know what to call that, but it worked and it changed my relationship with food forever (in a good way). I have since kept the weight off and switched back to eating 3 meals a day with a better understanding of how much and of what to eat.
Eat a lot more protein and way less carbs. Most meats already have the right balance of fat included, so avoid adding more. Fill up on fibrous vegetables since they don't really count towards calories and help digest all the meat you'll be eating. Drink plenty of water, sleep well, and at least hit your daily steps and heart rate targets if you're not huge on exercise. Building muscle is a good idea, but I'm lucky I've never had a problem with that and just needed to lose the body fat.
I'm now in my mid 30s and have a clean bill of health. When I was heavier I was prediabetic and my resting heart rate was 85. Now it's about 65 and blood sugar is good and doesn't spike or stay elevated all day anymore. It's good to get this stuff on track when you're still youngish.
Oh also I stopped the intermittent fasting because it was messing with my blood sugar. That was why I wrote all this and it's my argument against it.
Now and then like twice a month, skip 2/3 meals in the day. If hard, have light juices/even fruits. Think of it as giving your digestive system "rest". Don't do it when otherwise sick.
It will make you generally healthier, no drastic changes. Those require drastic measures which differ person to person.
Losing a bit of lean muscle mass along the way is not important compared to the huge health gains of losing the weight.
When it comes to long term health outcomes, losing weight is the only thing that matters.
You need to be getting enough protein + strength training to maintain muscle in a caloric deficit
Regardless of how you lose weight the advice is and remains:
> Eat a minimum of 0.36 grams of protein per day, per pound of LEAN* body weight. Increasing to 0.5-0.7 grams of protein per day, per pound of LEAN* body weight for older adults or when undergoing weight loss.
*LEAN is a vital detail for overweight people, they commonly miscalculate protein requirements due to this. The easiest way for overweight people to determine their requirement, is just find an "ideal body weight calculator" online, enter height and gender, and then multiply THAT figure by 0.5-0.7.
For example a man who is 6' tall and 400 lbs should eat 62 grams of protein per day MINIMUM, but during weight loss 86-120 grams of protein per day. It is common, unfortunately, to read online people in this situation miscalculate this to 280(!) grams of protein per day which is incorrect and harms their weight-loss goals.
> Protein intake should range between 1.0-1.5 grams/kg of adjusted body weight. To calculate adjusted body weight, first calculate excess weight: Excess weight = current weight — ideal body weight (IBW). Adjusted body weight = IBW + 0.25 of excess body weight. This amount generally accounts for 20% to 30% of total caloric intake.
So a slightly more complex way of calculating roughly the same thing. I'd argue that for most people getting your ideal weight is a good enough approximation, and that using your overweight/obese body fat in your protein calculation is wrong by a lot no matter which calculation you use.
https://www.ajmc.com/view/chapter-2-clinical-nutrition-guide...
I’ve tried all types of diets. For me, the most important for me is to save the biggest meal for late in the day. I can easily go hungry a couple of hours during the day if I know there is a filling meal coming.
I suspect IF works in a similar way.
Wouldn't the big meal be stored as fat during sleeping?
Hunger is driven by hormonal signals designed to defend a set point. Even if you consciously fast for most of the day, your brain will push you to make up the difference once you start eating. When it comes to fat loss, it still boils down to maintaining a caloric deficit — timing alone won’t keep your appetite in check for long. We’ve known this for years.
IF may have other potential benefits — better insulin sensitivity, longevity, or improved adherence for some people (since avoiding food most of the day can be psychologically easier) — but none of that is “new” anymore.
There is some evidence that there are health benefits that are specific to the fasting mode. This has mostly been studied in the context of chemotherapy, where fasting can protect against some of the side-effects of chemotherapy:
https://pmc.ncbi.nlm.nih.gov/articles/PMC5870384/
Most of this has only been studied in animals, not humans, but in animals the results were clear:
"Fasting before chemotherapy (CT) was shown to protect healthy cells from treatment toxicity by reducing the expression of some oncogenes, such as RAS and the AKT signaling pathway [2]. This reduction is mediated by the decrease of circulating insulin-like growth factor 1 (IGF-1) and glucose. In addition, starvation and calorie restriction activate other oncogenes in cancer cells, induce autophagy, and decrease cellular growth rates while increasing sensitivity to antimitotic drugs [2]."
If we assume that we have been shaped by millions of years of frequent famine, then our evolution has been shaped by famine. It is possible that our immune system simply makes the assumption that we will soon face famine, and therefore some important tasks, such as extreme autophagy, are normally postponed till the famine arrives. However, in the modern era the famine never arrives, and so we may have to induce it by artificial means.
I have experimented with very long fasts. My longest fast ever was in September of 2015 when I managed to go 12 straight days on nothing but water.
Obviously, any health benefits from that incident might have been psychosomatic, since I was expecting health benefits. But all the same, I did find some of the health benefits to be shocking and completely unexpected. Since at least 1995, and possibly 1990, I had a mole on my skin on my left arm. I wasn't worried about it, so I simply ignored it. I had it on my arm at least 20 years, maybe 25 years. I recall one morning in November of 2015 when I was in my kitchen, making breakfast, and I reached over to pour myself some coffee, and of course my arm was in my field of vision, and after a moment of thinking something was different, it occurred to me that the mole was gone. It had been there at least 20 years, and then it disappeared, at some point during the weeks after I had done the 12 day fast. I don't know when it disappeared, it just slowly faded away at some point between September and November. There was no remaining sign of it on my arm.
Again, that might have been purely psychosomatic, but it was interesting.
[0] https://bahs.org.uk/AGHR/ARTICLES/59_23_Healey.pdf
Longer duration trials are needed to further substantiate these findings.
The combination of Keto+IF worked so well for me, for a while my calorie tracking switched from the usual preventing eating too many calories to ensuring I was getting enough, which was certainly never on my bingo card. After a lifetime of being a slave to hunger it was liberating to suddenly feel effortlessly in control of diet and my relationship with food changed completely. Then at around 90 days my palate shifted, meaning I even lost my taste for carbie foods. If I tried a small bite of something carb-laden that I'd loved my whole life, it didn't even taste particularly good to me anymore. I also became hyper-sensitive to sugar. Sugar-soaked foods just taste poisonously over-sweetened (which they kind of are). A slice of apple now tastes as sweet as I'd ever want, like a dessert that has extra sugar-added.
In the 8th month I reached below my ideal 'dream' weight and even saw abs appear for the first time in my life! I transitioned to maintenance mode but stayed keto because being in a blood sugar controlled state felt so amazing and not just physically but also mentally and emotionally. At around a year I went from strict keto to low carb for life which I still am 8 years later. When I started that was unimaginable. I saw keto as an onerous regimen that I'd endure if it worked and stop the second I wasn't overweight. But during the journey my metabolism, palate and food preferences changed so dramatically, I was basically a different person when I arrived. Those first few months when I was rigorously tracking every calorie in an app and managing intake with measuring cups and a kitchen scale felt like a burden but were actually invaluable skill-building. After a few months all that process became automatic so I didn't need to constantly track and by six months I got to the point where I don't even think about it consciously. That early rigor helped me get so in sync with my body and able to sense where my metabolism is in its natural cycles that now I just eat when necessary and convenient for my schedule. This often ends up being IF but it's not intentional on my part, which makes me think maybe IF patterns evolved in the hunter/gatherer era as part of our natural biological rhythms. Due to habit and carb-laden factory foods I'd never been able to access those rhythms until I made the conscious effort to break the patterns I'd been raised in.
I suggest you read the FAQ of the Reddit keto forum: https://www.reddit.com/r/keto/wiki/faq. I recently posted my personal "Keys to Keto Success" learned during my 8 month weight loss 8 years ago: https://www.hackerneue.com/item?id=44685689 which includes some effective hacks I discovered. The biggest thing is to do keto rigorously. It's different than most any other diet because it's not just about reducing calories. The power of keto is 100% in cutting carbs, which is why I advise "Cheat all you want on calories but never (ever) on carbs".
For me, cutting calories on any diet was always difficult, painful and exhausting. Keto worked because I only focused on cutting carbs. Once I got my blood sugar under control by limiting carbs, my raging hunger just evaporated and the calories pretty much took care of themselves. The change was dramatic. After the first month I was no longer tracking calories to stop over-eating but instead to ensure I was getting enough :-). During the second month there was a point where I was slightly concerned I might be losing weight too fast because I was never hungry, which was certainly never something I'd imagined would be a problem for me. Of course, that's easily addressed by increasing calories a bit.
There's just one thing to watch out for as you do keto. On keto you're able to eat a lot of fats which are very filling (and delicious). This is wonderful but it's only possible because having almost no carbs puts you in a ketogenic state where instead of burning glucose (carbs) for energy as you do now, your body burns those fats for energy instead of storing them (weight gain). So, unlike a normal calorie-reduction diet, where you can slip one day and just get back on the wagon the next day, cheating on carbs during keto will convert all that delicious fat you're eating into not only pounds of weight but potentially into all the bad stored fat related things like vascular plaque etc. So, basically, keto is the one diet where cheating doesn't just "delay your weight loss another day", it changes from magically protecting you from the negative effects of eating huge amounts of fat to actively making it much worse. Eating all that luscious fat thinking you're protected by Keto but then regularly cheating on carbs "just a little" (as many do on other diets), is pretty much the worst diet imaginable. You'll turbo-charge weight gain AND all the negative effects of excess fat consumption (cholesterol, lipids, A1C, etc). Theoretically, aggressively eating keto-levels of fat but NOT being in a ketogenic state to burn it off could, given time, make you pre-diabetic and your lipid blood panels will freak your doctor out.
So, IMHO, keto is wonderful but there's just one unbreakable rule. You really, really can't cheat on keto (even a little). When I first understood this I was a little concerned but as I researched more it made complete sense. Keto isn't magic. With all these benefits of easy weight loss and healthy metabolism of course there's a potential downside to avoid. Now you know what it is - so go in with eyes wide open. For me, the stringent, "can't cheat, ever" (on carbs) aspect of keto was actually a psychological benefit. It made it 100% binary and thus easy to fully commit. I'm either really doing this or I shouldn't bother. Putting tangible health consequences on regularly "slipping just a little" actually helped me stick with keto rigorously during the first few weeks of transition and habit change (which is really the only hard part, after 30 days keto gets much easier). But you may be different, so you just need to decide if you can really commit 100% for the first ten days. If you manage that, then set your goal to finish the month. The rest really is all downhill from there. If you're as overweight as I was, after the first month of strict keto your weight loss will be so obvious people will definitely notice. In the second month, my admin told me people at the office were asking her if I was "okay", like they were worried I had cancer or was on chemo :-). So I started sharing a little more widely that I'd changed my eating habits. At least nowadays most people have heard of keto.
One thing that I'm concerned with, is longevity when a person is on keto. Do you share this concern? Do you know any reliable data source on keto diet's impact on longevity?
I have no concern because there's nothing about a low carb diet that restricts any essential nutrients. On evolutionary time scales, consuming a significant amount of carbs is a recent and unprecedented change to human diets. There are three types of macro-nutrients: protein, fat and carbs. For most of history our hunter/gatherer ancestors ate far more protein and fat than carbs, which is why they were in a ketogenic state most of the time. It's only in the last hundred years in Western democracies that carbs have become overwhelmingly dominant in human diets. In terms of long-term dietary impact, highly-processed manufactured foods and intensive factory farming (which are mostly carbs) are the massive uncontrolled experiment on the broad population that's worth being concerned about. That's the new thing for which there's no long-term data whereas keto has tens of thousands of years of proven success in humans. Going from the Standard American Diet to keto is opting out of the uncontrolled experiment and returning to what we know works. Chronic obesity and Type II diabetes are diseases of diet and they weren't common in humans until the last hundred years.
As for my personal health and longevity, keto has certainly added at least a decade to my life because before keto I was significantly overweight and had been diagnosed with pre-diabetes, high blood pressure, high triglycerides and bad HDL/LDL. I also had chronic sleep apnea as well as IBS/GERDS. I was on five prescribed medications to treat these issues. By the end of the first year on keto those serious health problems had completely resolved and I was off all five medications. To be clear, keto itself isn't some miracle cure. These problems were caused by my obesity and unhealthy diet. Keto helped me not be obese and to eat a healthier diet richer in nutrients and with far fewer manufactured and processed foods. My previous diet was making me sick.
I can’t believe that losing 3.5 days of caloric intake would result in weight loss. In other news, water is wet.
Keeping this up is hard, many fail. Alternating normal eating with IF days is easier to do.