Available calories per day per pound of body fat?


(Bruce Pick) #1

Somewhere there’s a figure of potential calories generated Per Day, per each pound of stored body fat.

I remember a discussion of that in the Two Keto Dudes podcasts - how many calories can be generated per pound of stored body fat. Does someone here have a reference on that? I’ve been discussing this in a FB group but I can’t even find any notes I may have made on it.

The end result of this value is, if you’re 50-100 lb overweight, your stored fat can easily generate enough calories per day, to get you through the day. But when you have only, say, 20 lb body fat, it’s not enough to generate 2000 calories per day. Not even close. Probably not even half of the calories needed per day.


#2

This might be what you’re looking for. It’s fairly contentious. https://blog.2keto.com/why-fasting-is-easier-for-some-people/


(Chris) #3

A pound of bodyfat = 3500 calories. That’s why the common (and correct) instruction for a pound a week of fat loss is -3500 every 7 day or 500 calories. Of course the amount to lose a pound will likely vary depending on how long the person has been dieting and what their lifestyle outside of food is like.


(Michael - When reality fails to meet expectations, the problem is not reality.) #4

virta


(Bacon by any other name would taste just as great.) #5

[quote=“Dread1840, post:3, topic:107862”
A pound of bodyfat = 3500 calories.
[/quote]

Zoë Harcombe looked into this and debunked it. No one really knows where that figure comes from, and it’s apparently not accurate. At 9 kcal/g, a pound of body fat should contain 4086 kcals, anyway.


(Bacon by any other name would taste just as great.) #6

This post by Richard sheds some light on the matter:

He also has a post in which he calculated the maximum amount of energy the body will allow to be drawn from its reserves, but I haven’t come across it yet.


(Michael - When reality fails to meet expectations, the problem is not reality.) #7


50%20AM


#8

I’ve read 7kcal/g as fat tissue isn’t pure fat…

But it’s not about calorie deficit vs fat loss, it just went into that direction quickly. The topic is how much energy we can get out of our bodyfat per day. Tons of energy is there, if only that would matter, I could be fine for months without eating (except I still need the essential nutrients) - and I am not.
Many leaner people can’t even fast for 2 days but some can so it’s complicated :slight_smile: There is a formula and that fails in many cases.


(Michael - When reality fails to meet expectations, the problem is not reality.) #9

Link posted by @TheOrangePimpernel in first response to OP.


(Bacon by any other name would taste just as great.) #10

I was thinking of a particular forum post, actually, but I wouldn’t be surprised if the blog contains the same info.


(Doug) #11

Bruce, the link that TheOrangePimpernel posted is one way to see it - the calculation was roughly 28 to 34 calories per day per pound of body fat. The study was based on Ancel Keyes’ Minnesota Starvation experiment, and I wish there were better, newer experiments to confirm, broaden, nail down the results, etc. Keyes didn’t look at fasting people - he restricted a bunch of guys to 1570 calories for six months. It would be good to see what happens with people when truly fasting.

It does make sense that there is a limit on how much fat the body will/can burn in a day. The need to conserve energy from a worst-case situation, i.e. needing to keep the body alive, would explain why we are evolutionarily wired this way.

I think you’re right about relatively lean people not having enough fat to supply all their energy needs, and in general they do seem to have a relatively hard time fasting for multiple days.

Our fat actually is very close to 9 calories per gram. And indeed - our adipose tissue is 87% fat. 454 grams (one pound) x 9 calories x 87% = 3555. So, very close, to begin with.

Longer-chain triglycerides are more calorically dense than shorter-chain ones, and we have a mixture of them in our stored fat. But it’s not too mysterious - over 90% of our stored fat are the triglycerides with 16 or 18 carbon atoms, palmitic and stearic acid.

When fasting, most people lose right about a half pound of fat per day. This is quite consistent, with bigger people and people with a LOT of fat losing a little more. Some extremely obese people, on long fasts, have lost 0.6 or 0.7 lbs per day of fat.


(Sama Hoole) #12

The formula itself does seem a bit sketchy, but the principle makes perfect sense. The leaner you are, the more suppression you pick up during extended fasts.

Once I got below 10% bodyfat, any fast over 24 hours just sent my body into shutdown.