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Comment by bagacrap | Hacker News Reader

This is misleading. If they don't eat as much due to higher satiety, then you are not replacing with equivalent calories.

Calories are meant to be and are calculated as the lingua franca of macronutrients. 5 calories of one really will have the same effect on your waistline as 5 of another, holding all else equal.

Regardless, the grandfather is discussing macronutrient distribution and you seem to be in favor of optimizing it as well, so I don't think there's disagreement here.

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The thing most “a calorie is a calorie is a calorie” people miss is that, according to the Low Carb, High Fat hypothesis, different types of calories affect the rate at which you expend calories. So, the theory is that a high fat diet makes more calories available as fuel and your body responds by making you feel more energetic, which leads to behavior that expends more calories. Whereas high carb diets, because of the way the body processes carbs, make less calories available as fuel and your body responds by making you feel less energetic, which results in behavior which expends less calories. So a calorie is not just a calorie.

That’s the theory, at least.

> If they don't eat as much due to higher satiety, then you are not replacing with equivalent calories.

That's one factor of why eating fat instead of carbs defeat the calories-in-calories-out idea. But it's not the only one. Both the lack of release of insulin and ketosis helps the body work much better.

> 5 calories of one really will have the same effect on your waistline as 5 of another, holding all else equal.

That's the problem, nothing else is equal when you have a vastly different proportion of macronutrients.

OK let's ignore protein for a second. You're saying that if you eat the same number of calories, but as fat instead of carbs, your body will store less of it. i.e. that the human body is much more efficient at extracting energy from carbohydrates than it is from dietary fat, i.e. more of the energy from dietary fat is wasted. Macronutrient choice cannot affect the amount of work that your body does, only what percentage of the calories are wasted (inefficiency).

On the face of it this makes no sense because fat is such a good energy source that it's what our bodies use to store energy, so why would our bodies have problems extracting energy from dietary fat?

I didn't say that our bodies extract less energy from fat. It stores less energy as fat. Fat storage mode is stimulated by insulin, which is stimulated by glucose or by lack of sodium. Insulin brings other health problems in addition to weight gain.

See my other response, but the theory is that high fat diets make more energy evailablw for use, rather than storing it in adipose (fat) tissue. This makes someone more energetic, which is how a high fat diet can result in weight loss at the same calorie intake, but still have the energy balance equation work out.

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