Comment by philwelch | Hacker News Reader

Comment by philwelch | Hacker News Reader

> Even the 150 doctors, dietitians and personal trainers we surveyed shared this surprising gap in their health literacy. The most common misconception by far, was that fat is converted to energy. The problem with this theory is that it violates the law of conservation of matter, which all chemical reactions obey.

For reference, if losing 10 pounds of body weight corresponded meant it was converted to energy completely, that would produce about 4 * 10^17 joules of energy. That’s equivalent to 95 megatons of TNT (or two Tsar Bombas) or 111 million megawatt hours.

> The only thing in food that makes it to your colon undigested and intact is dietary fibre (think corn). Everything else you swallow is absorbed into your bloodstream and organs and, after that, it’s not going anywhere until you’ve vaporised it.

This is an oversimplification; if digestion was 100% efficient, feces would be sterile. I think there are even bariatric surgeries that work by making the digestive system less efficient.

> This is an oversimplification

It's perhaps the most pernicious misunderstanding of calories on the internet.

All calories are not created equal. Even just taking the same ingredient (say, an apple) and preparing it (say, by sticking the apple in a Blendtec Blender vs eating it whole) changes the amount of calories available for absorption.

Right. Fiber is a debatable source of calories since their precise metabolism can change based on gut flora. As someone who lost 100lbs through calorie counting and exercise, just that subject alone was a long and interesting study. Some nutrition labels will assign them 0 calories, a seemingly benign 10 calories, or the same calories as other carbohydrates.

https://www.verywellfit.com/why-are-there-calories-in-solubl...

https://www.bodybuilding.com/fun/ask-the-macro-manager-does-...

Is it safe to say that taking an apple and manipulating it without adding anything to it could never INCREASE the calories available?

So is the reason that the calorie content in the apple changes in blending due to how difficult (or not difficult) it is to digest?

> could never INCREASE the calories available?

It wouldn't add calories, but it would make more calories available in the sense that your body is able to extract them.

For instance, cooking food makes more calories bio-available.

No, blending it increases the calories available to easily absorb. This is partly why juicers are unhealthy.

Basically. It's similar to how we typically process meat without adding anything to it before eating it, to make it easier to digest and to increase the available calories.

The way we process it is by cooking it.

What do you mean by "available"?

Fire was an important technology because it allows us to predigest food, getting more out of eating the same amount of stuff. This certainly does increase the calories available in the ordinary usage of the phrase -- but so does the blender example.

A blender is a bunch of knives. Just something else enabled by fire.

Do we approximately know by what percentage the calorie availability increases for blended vs regular fruit, for the average person?

> This is an oversimplification; if digestion was 100% efficient, feces would be sterile.

Generally 10% of energy is conserved when moving from one trophic level to the next. [1]

[1] https://en.wikipedia.org/wiki/Ecological_efficiency

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