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Comment by apinstein | Hacker News Reader

tl;dr version:

Calories derived from fat vs protein vs carbohydrates have different inefficiencies in converting them from their theoretical caloric value to their useful work in the body.

Fat is the most efficient with a loss of just @ 2-3%, carbs are at 6-8%, protein 25-30%. [edit Most of] this loss is in the form of heat.

It was not mentioned why this excess heat would not simply be offset by the body avoiding the normal processes it takes to maintain body temperature. Presumably the body generates enough heat as a by-product at room temperature and thus there is nothing the body can back off of to make use of the waste heat described above.

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Funny, I learned this in nutrition class about 20 years ago. It's something that clearly has been known for a long time, yet its never been popuar in the common discourse.

Exactly. I also believe it doesn't really matter, because the inefficiencies of converting sugars to body fat are pretty much irrelevant. Proteins may have a more significant inefficiency, but it's hard find food where they are the majority component.

When people overeat grossly, those 5% won't make much of a difference. On my binge days, I consume upwards of 5000 kcal and it doesn't really matter if it's actually just 4750 kcal - it's still too much.

So yeah, in practice, a calorie is pretty much a calorie.

Huh? Just because one can binge so much that the difference is irrelevant hardly means that the difference isn't important in general.

The study this cites early on suggests that a low-carbohydrate diet with N calories a day is roughly equivalent to a low-fat diet with only 70% of N calories a day. So a 2000 calorie-a-day low-carbohydrate diet is equivalent to a 1400 calorie-a-day low-fat diet. That result is huge. (And makes me regret having had pasta three times this week!)

I allege that it indeed makes very little difference, except in cases where people indeed manage to eat only one category (most food is a mix, even when people claim to be on a <insert here> diet).

As other people said, the results of this study are not new. We learned that in basic biochemistry when the metabolic pathways were discussed.

> So a 2000 calorie-a-day low-carbohydrate diet is equivalent to a 1400 calorie-a-day low-fat diet.

It is so not.

"A low carbohydrate group (LoCHO = 1800 kcal for men; 1500 kcal for women), a low fat group (LoFat, 1800 and 1500); a third group also consumed a low carbohydrate diet but an additional 300 kcalories were provided (LoCHO+300, 2100 and 1800). The order of average amount of weight lost was LoCHO = 23 lbs, LoCHO+300 = 20 lbs LoFat = 17 lbs." That's not quite the same math I used, but it seems to pretty strongly suggest that a LoCHO+600 group would have have lost 17 lbs, exactly the same as the LoFat group.

Perhaps there is some reason to doubt this study, but saying "It is so not" is hardly a rational rebuttal.

Provided you assume those effects are linear, then yes. There is however no evidence for that.

FTA:

> Some of the available energy is lost as heat and in the internal rearrangement of chemical compounds and other changes in entropy.

So not all of the difference in efficiency is made up in the form of heat. Unfortunately, I don't remember enough biochemistry nor thermodynamics to dive deeper into this, but I think this article is a good starting point for a discussions, which has otherwise just been dismissed with the "a calorie is a calorie" argument.

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