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Comment by hector_vasquez | Hacker News Reader

How are you defining a "calorie"? The number printed on the package? Because that number is basically meaningless.

That number happens to be remarkably accurate. More accurate than required by law in fact. It also happens to accurately predict changes in a person's weight if you know everything they're eating.

A question I've had that I never really looked into or found an answer to:

How does calories in vs calories out work regarding the energy left in food that is not extracted (i.e. the caloric value of poop basically).

Is digestion / energy extraction pretty consistent throughout the population or do the specifics of people's digestive systems play a role in how many calories are actually available to the body?

Basically, would a constipated person's digestive tract pull more energy out of the food since it is in the intestines longer?

While it certainly differs from country to country, FDA allows a discrepancy of 20%. That's significant. There have been studies that showed the labels to be off by 25%.

And even if the numbers were accurate, they're still rule-of-thumbish, because human metabolism doesn't simply ingest all energy available in a food. For instance you'd absorb roughly 40% more calories from peanut butter than from actual peanuts (of the same calorical value).

There are more reasons why counting calories isn't nearly as accurate a method as people tend to assume, but these two are really sufficient.

Isn't the low carb argument that for proteins more is passed and don't need to be burnt off, but for carbs almost all calories must be burnt off? How many calories do I take in and therefore must burn off thru exercise if I swallow a penny?

I think the low carb argument is that processed carbs mess with your blood sugar levels, making you hungrier, but the discourse around nutrition is messed up enough that there are many low carb arguments, some of them mutually contradictory. As for your penny, zero, unless I'm greatly mistaken, which is why pennies don't come with nutritional labels.

THE low carb argument is ketosis. That's not even controversial. If you look it up on Wikipedia, it's described in a very aseptic way, it just a basic fact of metabolism. If you look at low carbs diets articles instead, a cloud of disinformation appears.

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