What are the advantages to longer interval fasts (+3 day fasts) as opposed to extreme deficits (<1000cals p/day)?
I’ve seen success stories from people who did intervals of three days of fasting with a one day refeed, but how is that better than just eating at low calories every day for an entire week/month/year?
According to Jason Fung, the argument is that fasting reduces insulin and allows the body to access fat reserves. As a result, the body has access to enough calories to continue running its processes as usual, and does not severely downregulate its metabolism. There is some work by (iirc) Lustig showing alternate day fasting maintains metabolism while simple calorie restriction crashes it.
The issue with calorie restriction is you’re caught in the worst of all worlds: you’re not taking in enough calories to maintain your body, and if you’re consuming “normal” food your insulin levels stay high. High insulin prevents access to fat reserves, so the body cannot get access to enough energy. As a result, it downregulates its metabolic rate. This effect can linger for years after you stop, and is a large cause of the rebound weight gain dieters have and why diets fail. Even if you eat fewer calories later you will gain weight as your metabolism has downregulated.
All of the above just speaks to weight loss. There are other benefits to fasting such as autophagy which won’t kick in if you’re eating each day (unless you’re being really careful and following something like a fasting mimicing diet).
At a subjective level, to me it seems easier to just fast than consume a small amount of calories each day.
It’s my understand that prolonged low calorie intake will cause your body to simply use less calories, but fasting won’t (because of some reason I don’t know). Please someone post proof of this theory, because obviously I don’t have the whole story.