How much body fat do you need for extended fasting

(Attila N Abelovszky) #1

Diving in with my first post.

I have been Keto for about two months know and feel I am fairly well fat adapted. I am thinking of starting my first extended fast 2 or 3 days. One thing I am not clear on is what happens if you do not have enough fat to maintain your energy needed. I am currently 195 lbs 146 lean 49 fat. From the numbers I see it seems like I can produce about 1543 kCals of energy a day (49x31.5). My normal requirement is probably around 2200 kCals a day. So what happens with people with too low of a body fat. It seems like I have heard plenty of interviews now with athletes on the podcast who do not seem to have issues and they probably do not have that much body fat.

So where does the rest of the energy come from or am I missing something.

Attila

(Allie) #2

This is why people who are fairly lean sometimes supplement fat on fasts, but from listening to Dr Fung on padcasts, if I remember correctly, he mentioned the lower limit being in the low teens of bodyfat for men.

#3

I’d like to know this as well. I am about 24-25% body fat (female), but having trouble doing fasts beyond 24 hrs, which I could do before. Seems like 25% should be plenty and yet I am so cold and miserable.

(Jennifer) #4

Give this a read. It should help but it is still an estimation. Some folks have long term fat that their body really doesn’t want to give up. Or can’t find to use… lol.

(Tina Emmons) #5

The number I heard from Fung is one pound of fat will last you two days on a fast(which makes sense calorie-wise) so a two to seven day fast isn’t going to kill most of us.

(Attila N Abelovszky) #6

True. But it seems like your utilization is only 31.5 kCal per pound of body fat. So while you have plenty of fat to burn. It is the utilization that matter. Which for me seems to be about 1550 a day. So that implies I am running a deficit for energy. So I would think I would need about 500-600 kcal per day that is not provided by fat storage. The question that is not getting answered is where does this come from. If it is addtional glucose or ketones produced by the liver no big deal. If at some time it is lean muscle mass that is a concern.

(Tina Emmons) #7

Answered in Richard’s blog post above. Interesting!