0.1% of 1 million calories is 1000 calories, which corresponds to about 0.3 pounds. If someone gains or loses 10 pounds in a year, that means they were around 35000 calories away from equilibrium throughout the year, which is more like 3-5%.

So a 5% calorie deficit or surplus would have a fairly small effect during a single year, but over a decade or a lifetime the effect is huge.

oops, I sure got my digits wrong

It is exactly how it works, and you're taking "a small percentage" to a ridiculous degree to fallaciously disprove it. Try eating 10% more or less than what you need each day, not 0.1%.

Another question to pile onto this. Maybe you're the right one to ask.

I was always taught that the body uses up its glycogen stores before burning fat. But if that were true even a small calorie deficit would gradually use up our glycogen stores and we'd be walking around without any after that.

Plus before losing any fat you'd have to experience a glycogen crash/wall which most small deficit dieters don't experience.

Very roughly...

Generally what fuel your body burns depends on the intensity of work you are doing, so if you're walking you may be burning 80%+ fat, but if you're running a 10k you may be 80% glycogen.

However, if you eat too many carbs at a meal (beyond what you need in the next few hours), your body needs to get that excess out of your bloodstream, so it will do a combination of: - fill your muscle/liver glycogen stores (limited size) - burn any excess carbs in preferences to stored fat - convert any excess carbs to stored fat

Once it's got rid of the excess carbs from your bloodstream, it will return to burning whatever the normal ratio of fat:carbs is for you.

Consequently, if you always eat too much carbs, you'll gradually pile on the fat, unless you're doing large amounts of training which depletes your muscle/liver glycogen, e.g: elite athletes.

Actually, that IS how it works.

It may not be possible to know or calculate the exact intake and output values, but those values are not needed. Your body gives you cues.

> eating a little more or less has absolutely not discernible effect the body adapts to it.

Yes, the body adapts to it by storing or eliminating fat (among other things).

No, if that was true people would be always over or under the weight as it's impossible to know exactly how much calories the body consumes.

> Yes, the body adapts to it by storing or eliminating fat (among other things).

No, it compensates by changing your metabolic rate mostly. You eat less, you will feel more lethargic, you eat more and you will fill (and be) more active

1 billion*

2 - 2.5 million calories a day is normal for people with a normal level of physical activity.

In the US, we tend to use food calories, where 1 Calorie == 1 kilocalorie. The capitalization of Calorie is intended to show the difference in units, but in most written language, often isn't used.