I'm really interested in how time-restricted eating and extended fasting affects people who are very fit or don't have much weight to lose. Many people say "lo

I'm really interested in how time-restricted eating and extended fasting affects people who are very fit or don't have much weight to lose. Many people say "low-calorie diets" extend lifespan, but I highly doubt, because once you reach a low enough bodyfat you actually experience lots of negative effects (which are actually similar to a high bodyfat). Maybe it's correlation, because the people who eat lower-calories have a lower natural metabolism which makes them age slower? But fasting isn't the same as low-calorie. Anecdotally in my experience fasting really does help short-term: I have more energy and better mood and feel "lighter". Maybe because my body doesn't have to spend energy digesting food. But if I fast too long or often I start to "crash". And once I start eating I usually also "crash". The latter is probably because I usually eat a big meal, but if I don't eat a big meal I would continue dropping too much weight and cause the former. Fasting also screws up my digestion, because when my digestive system restarts it starts slow and gets backed up more easily - the same meal breaking a fast leaves me bloated and lethargic, which I handle fine after a while of eating regularly.