[arcticbull]

The problem with severe caloric restriction is that your metabolism slows down. This isn't true of water fasting up to 4-5 days at a time where your metabolism increases ~10-15%, and your body produces significant quantities of HGH which help you burn fat while preserving muscle.

Severe caloric restriction diets are actually not particularly effective if your goal is to permanently lose significant quantities of weight and keep it off - once you plateau it really sucks. Of course I mean if you power through and keep at it you will, but IME, periodic fasting is a much easier way to lose weight and keep it off.

Not hazardous, really, as you point out. The whole point of stored fat is to be used.

Citations available on request, I have NCBI links for each of my points but it takes a while to dig up.

[ilyt]

I've tried many things and I prefer intermittent fasting over diets and calorie counting. Changing diet a bit is still important (cutting carbs and focusing on stuff that keeps me satiated for longer), but it's easier to manage say going to event (just fast day before/after), or when having some bigger meal for whatever (socializing etc) reason I can always just eat later tomorrow.

Usually one big meal after noon and that's about it, plus occasional coffee or cup of cocoa. If I have event in the evening I just don't eat during the day or get a milky beverage to get me by, then depending on how much I ate I either delay dinner the next day or skip the next day altogether.

[strken]

What's severe caloric restriction mean, here? From memory I've read that 750kcal and even 1000kcal under TDEE are effective. A TDEE of 2400kcal would be normal for a young 6'2" male who does a bit of light cardio, and 2150kcal wouldn't be unusual for someone who's sedentary.

[arcticbull]

Some studies, including one that followed The Biggest Loser contestants [1] showed that your basal metabolic rate goes down as much as 23% as a result of significant caloric restriction and remains lower for at least the 6 years of the study - even if the weight is regained. For these contestants the restriction was very significant, though I'm not sure if it's quantified in the study.

Here's another interesting one. Check out the Energy Expenditure section of [2].

> The gross BMR decreased in all the subjects during semistarvation, the average decline being 17.1% after 19 days (54) and 21.4% after 13 days (55). [3]

Based on this data, I would expect your BMR to go down by 20% over a period of three weeks, and remain there for the rest of your life were you to continue this for a while. So you'd have to, as an 'average' person, reduce intake by 500kcal to account for metabolic adaptation, then another 500kcal to lose 1lb per week.

That aligns with your suggestion that 750kcal-1000kcal reduction should show results for most people.

[1] https://pubmed.ncbi.nlm.nih.gov/27136388/

[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3673773/

[3] https://journals.physiology.org/doi/abs/10.1152/jappl.1958.1...