My criticism is basically this: there are places where people live longer than others, and they certainly aren’t eating bowls of green goop and 200 pills every morning. If your goal is to maximize longevity, it seems logical to imitate whatever they’re doing. Or at least investigate it.
Why do you think it goes against "conventional longevity advice"?
I am not saying it's bad; eating fewer calories has its benefits. However, the effectiveness of intermittent fasting, especially as portrayed in the media, has been quite overblown, IMHO. I think one of the main sources of this is from a study that suggested longevity improvements in lab mice. Unfortunately, studies involving lab mice, especially those concerning metabolism, translate poorly to humans.
I think you're referring to 'Blue zones'[0] here. I'm certainly not an expert in longevity, but was also intrigued by these areas and their apparently above-average lifespan, and how it goes against a lot of conventional longevity advice re: diet.
One explanation I've heard is that they're simply the results of poor record keeping, and that there isn't much strong evidence to suggest people in those regions do statistically live longer than average.
[0]https://en.wikipedia.org/wiki/Blue_zone