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Comment by DiggyJohnson | Hacker News Reader

Uhhh

Output / energy is the consensus definition of what it means to be efficient. The commenter you are replying to is being kind, but I guess I’m a little more callous…

Are you comfortable continuing with such a confusing definition of efficiency?

My opinion is that you are not recognizing the value of operating in a less-efficient (lower MPG, more power) mode. We can all spend more or less energy in a day as a function of the things we do. To me, it seems like you’re not recognizing this fact.

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I think what you're missing here is that upkeep (the numerator in your equation) is largely constant. It can change a little bit, but it can't go anywhere near zero. This is why it can be ignored.

As I said above, the bulk of calories consumed in a day for a typical person are upkeep, not exercise related. You do not need to factor it into the overall equation. The changes are not significant enough.

"Starvation mode" theory is that the upkeep of the body changes significantly when calories are lower, preventing the body from losing weight. It's just not true. There are secondary effects (lethargy, no energy for increased exercise for athletes) but the vast majority of obese people do not exercise significantly to begin with so these effects can likewise be ignored. The baseline caloric upkeep -- which is something like 70+% of calorie burn for almost all fat people -- will never significantly change in terms of its efficiency. This is why you will always lose weight on a calorie restricted diet, even without exercise.

Hopefully this clears things up for you.

There is a surprising amount of upkeep that can be forgone if needed. Muscle, nail and hair growth, reproductive functions like menstruation or sperm production, reducing energy use in the brain (malnourished people often report brain fog). I've also read about slower healing and being more prone to infections, so there's probably some general system overhead that is cut.

Of course, this is no way to live long term, but in a starvation situation it makes sense to reduce energy demand to the absolute minimum

Yes, certainly. But those do not account for a significant change in the baseline consumption of calories. The baseline need remains significant, despite the body's attempt to cut corners. It's not a question of whether the body tries, it's a question of how effective it is -- and it's not very.

Those effects I believe are also correlated with extremely low bodyfat moreso than a calorie deficit diet. In most cases a healthy person's body will simply consume fat to account for a deficit in the diet.

We unfortunately have a lot of data about starvation. The effects on the body are very clear. Body fat will go first. Most americans are in absolutely no danger.

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