Hacker News Reader

Comment by yummyfajitas | Hacker News Reader

If this is true, why don't we become incredibly fat or skinny over time? It would require incredible precision to maintain weight. But a lot of people seem to be able to do it with no effort...

Because the amount you require for maintenance is proportional to your bodyweight. If you eat more than you need, you become fatter. As you become fatter, the amount of calories you need for maintenance goes up as well.

The calories in/calories out theory explains weight stability perfectly. Thermodynamics is sufficient, no complex theories required. I do the math here: http://www.chrisstucchio.com/blog/2011/weight_stability.html

View on HN

That's all true, but still irrelevant to the question of fixing the obesity epidemic.

"Calories eaten per day" is not a free variable. It's governed by a control loop within the brain. In a healthy person, appetite adjusts to compensate for calorie surplus or deficit. We have an epidemic because that control loop is getting damaged. People have a hard time discussing this because they treat it as a moral issue. But it's clear that recruiting our frontal cortex to count calories should not be necessary -- every mammal needs to automatically maintain homeostasis, and does so just fine in its natural environment.

And "calories burned per lb bodyweight" is also not a simple constant. It has been observed swinging significantly. A starving person's metabolism will slow dramatically to conserve energy. An overfed (healthy) person's metabolism will ramp up and favor burning the excess over storing it.

So of course we can't cheat thermodynamics, and of course eating less matters. But how to eat less is an animal behavioral question, governed by biochemistry.

Your theories about other mammals are utterly wrong - many mammals get fat in the summer and come close to starving during the winter.

As for the rest of your post, I'm not sure what you are trying to say. The human brain is made of biochemistry, so therefore choosing to eat less is a biochemistry problem? Um, sure, I guess.

The Harris-Benedict study is from 1919 on a population of 239 subjects . I'm just wondering - Do you know if it has been re-evaluated in more recent years, and was found valid?

Last time I looked into it was a years back when I had access to a university library. I dug up a couple of textbooks on sports medicine, they all generally agreed that Harris-Benedict was a good first order approximation.

In practice, it's good enough for a fat guy trying to get thin. It might not be good enough for a heavyweight trying to get down to cruiserweight without losing strength.

Great link. I wish more people discussing health, exercise and diet took such a rigorous approach.

Reply on news.ycombinator.com