# Human Fat Adipose Tissue: Maximum Energy Transferred out per Day?

The article "A limit on the energy transfer rate from the human fat store in hypophagia" states that subjects with moderate activity levels are found to have a limit on maximum energy transfer rate from human fat stores of 290 kJ / kgd. This results in 31 kcal / lbs.

Question: Does anyone know (possibly with access to the full article) if above numbers are kJ/(kg body fat) or kJ/(kg body weight)? Optional, the article mentions moderate activity, what happens in the case of high activity?

I asked because if its kJ/(body fat), then this limits a 185 lbs male with 27 lbs body fat to 837 kcal/day metabolized from fat adipose tissue into energy, limiting his weight loss to about 2 lbs/week. If it's kJ/(body weight), then a 185 lbs male can transfer 5723 kcal/day from fat adipose to energy and lose about 13 lbs / week. Rough calculations made where 3500 kcal deficit = 1 lbs weight loss.

I have information that suggests a person without any food, only water, performing moderate exercise of 6 miles walking per day, for three weeks, loses about 4.3 lbs/wk (accounting for the loss of 11 lbs material in colon). This data suggests:

They either:

1. This examples uses energy from breaking down muscle tissue over the 837 kcal/day limit (fat store max) suggesting this article calculates using kJ/(body fat weight).
2. This examples uses energy over 837 kcal/day, which was 2344 kcal/day from the fat store, not including muscle tissue, suggesting that this article calculates using kJ/(body weight).
• If I understand correctly, what you actually want and need is the access to the full article. There are various ways to do this: either contact your library, a friend working at the university, directly request it from the authors, or ... well, there are also other ways which should not be publicly promoted, but are available online. Jan 9, 2023 at 21:33
• I have full access now and my suspicion is that the result is a max of 837 kcal/day/lbs body fat can be transferred from fat adipose tissue per day. This suggests that maximum weight loss of adipose tissue before using energy from free fat mass (skeletal muscle) is about 1.6 - 2 lbs/wk. I suspect people dieting should know this..
– Nick
Jan 10, 2023 at 3:39

Paper

From the conclusion: "The main thesis of this paper is that the FM is able to transfer energy to the FFM up to a maximum rate of (290±25) kJ/kg d."

Where FM is fat mass and FFM is fat-free mass.

So (290±25) kJ/kg d or (31±3) cal/lbs d is the maximum rate of energy transfer possible from FM to FFM where the kg or lbs in question are that of FM.

Example

I weigh 175 lbs and my body fat percentage is 10%. That means I have 17.5 lbs of FM. My theoretical limit of energy transfer from FM to FFM is anywhere from 17.5 * 28 = 490 calories per day to 17.5 * 34 = 595 calories per day.

That's:

• Min: 490 cals * 7 days = 3,430 cals per week
• Max: 595 cals * 7 days = 4,165 cals per week

So if we take 1 fat lb at 3,500 calories it's 0.98 lbs to 1.19 lbs maximum fat loss per week.

Dr. Alpert Later Remarks

Here's the thing though, the late Dr. Alpert went on to later state he miscalculated the numbers in the paper and it was more like 20 cal/lbs d to 25 cal/lbs d. Unfortunately he didn't republish the paper though.

Personal Experiments

I highly recommend performing your own experiments as the paper was done for a somewhat esoteric sample which was very small. A friend and I ran two personal experiments that might be of interest using DEXA scans to see how our results add up to those in the paper.

I followed a progressively restrictive deficit until I started experiencing muscle loss. I collected 7 intervals of scans. For me the maximum amount of fat loss was in fact 21 cal/lbs.

Interestingly enough once I experienced muscle loss my body started upregulating how much muscle it utilized and preserved fat which caused my fat utilization to drop all the way to 9 cal/lbs. I theorize this is some sort of evolutionary switch as I am very muscular. The body probably senses an "emergency" and starts preserving fat while utilizing muscle. Given muscle consumes more energy to maintain than fat, this seems like it would kill two birds with one stone for increasing the chances of survival.

My friend did a more extreme test where he fasted for 7 days and measured the FM change. He was able to hit 23 cal/lbs d of fat loss so it matched the paper very closely as well. His FFM was all over the place during the experiment but it's tough to tell what was water, carbohydrate, glycogen, etc. loss so we only looked at how much fat he lost.