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This question originally appeared on Quora. Answer by Bart Loews.

First let’s examine your assertions:

I know that you need to use more calories than you are intaking

So far, so good.

also eating fat or protein is better than sugar for this purpose.

Not necessarily. Fat has more than twice the number of calories than sugar and protein.

The major benefit to eating fat or protein, in many cases, is that it seems to, in some people, regulate your appetite better. That doesn’t mean you need to go engorge yourself on fats and proteins, quite the opposite. You still need to regulate your intake, regardless of your macros.

The simple answer is genetics.

If we assume that two people are eating the same, and one person is “burning fat better” the reason for this is, naturally, that they’re using more energy than the other person.

This is likely due to an elevated basal metabolic rate. There’s something innate to that person that causes their thyroid to produce more hormones up regulating the energy consumption rate.

There are several big assumptions, though.

Cases like this in the wild aren’t well controlled. You don’t really know how much these different people are eating, and you really don’t know how much energy they’re burning through activity, other than the fact that they have the same sport background.

Additionally, you’re assuming that they’re “burning fat.” Many fit people aren’t actively trying to lose fat, they are simply maintaining their fat level.

In most cases this metabolic boost is something that fades with time. I was a skinny little twig growing up. I’d engorge myself on Oatmeal Creme Pies and Coke through high school and stay at 10% body fat (I was swimming 18 hours a week, too). I got to college, stopped swimming, but didn’t change my eating habits. I blossomed by about 60 pounds by my sophomore year.

Some people have actual disorders, like hyperthyroidism, that make it very difficult for them to maintain weight. It sounds like a blessing, but it’s anything but.

Calories in < Calories out

It’s still the same rule for everyone. The big difference is that the Calories out isn’t the same for everyone, and it’s not always something easily observable.

The final note I’d like to leave is that you shouldn’t look at a person and draw conclusions about their habits, behavior, or even genetics based on a glimpse of their life.

Many people are quick to write this:

The Rock Quora

off as “genetics” when in reality, it’s a whole lot of this:

Body building Quora

and this:

The Rock, eating. Quora

Can you smell what The Rock is cooking?

People like to blame “Oh, I’m an ectomorph” on their inability to gain or “oh, I’m an endomorph” on their inability to lose. It’s simpler, and not as simple as that.

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