Not all hungry people, no. But anecdotally, a person that lives in my household has a body temperature that routinely measures 96 to 97 degrees Fahrenheit, well below the 98.6 degF that is considered normal. That person is overweight, and frequently attempts to restrict calories. So I didn't pull it entirely out of thin air.

The point is that energy expenditure is a function of foods eaten. You already accept as given that energy input is a function of foods eaten. You may even accept that energy input is not exactly equivalent to the combustion energy of the food.

So you still haven't answered my question.

Is ( f(x) - g(x) ) less than or greater than ( f(x/2) - g(x/2) )?

You cannot answer it. You do not know how the functions f and g work. Likewise, you cannot say that cutting food intake in half will result in weight loss.

Turning down the thermostat and increasing exercise will actually work, as a couple of those thermodynamic inevitabilities. But they still don't address the psychological barriers of weight loss. People don't want to feel hungry, or cold, or exhausted. If they are required to do so to lose weight, it probably won't happen, as being too fat causes them less acute discomfort than the effort to not be too fat.

It is unwise to compare their perception of their discomfort to your perception of your discomfort, in the same way that it is unwise to compare the pain from that one time you got a compound fracture on your agony bone to the pain of a woman in labor. Even if you were objectively hurting more, you just don't do it. Danger, Will Robinson, Danger!

Give encouragement, not advice. Most of the time, a fat person knows exactly what he must do to not be fat. He just doesn't want to change his lifestyle to something that is guaranteed to be subjectively worse and more difficult for months--or even years--before it even gets back to his current level of comfort. He may be angry and frustrated at himself for not being able to do it; that anger is all too easily projected onto other people or things. You really want to help, but there's really not much you can do, other than stand back and play "Eye of the Tiger" at them.

> The point is that energy expenditure is a function of foods eaten.

But there is a lower bound. If you carry some bags up the stairs, drink cold water and excrete warm sweat, inhale cold air and exhale hot there is some value of energy that you had to expend that's calculable by physics only.

Also energy intake is a function of lot's of stuff but it is not higher than the energy you could get from food by burning it (also calculated by physics or rather simple chemistry).

If you choose foods and activities so that there is a match between the upper bound of intake and lower bound of expenditure you will loose weight. That sounds like a sure recipe for weight loss for me.

> But they still don't address the psychological barriers of weight loss. People don't want to feel hungry, or cold, or exhausted. If they are required to do so to lose weight, it probably won't happen, as being too fat causes them less acute discomfort than the effort to not be too fat.

Yeah. You are right. But what makes me wonder is why gut reduction surgery works. If people physically can't eat as much as they are used to, they somehow magically are able to bear all the consequences of extremely low energy intake. They don't stuff themselves with pure sucrose and lard to maintain high calories at reduced volume.

> Give encouragement, not advice. Most of the time, a fat person knows exactly what he must do to not be fat.

Fortunately I don't know any fat people that I could hurt by my simplistic approach to what is for me almost purely intellectual problem.

What always made biggest difference for my weight was routine changes. Public transportation or cycling or walking instead of car for commuting, skipping the lunch, unsubscribing from meals cooked by my mom, not buying cheese. That's what I would advice. Skip some meals, change the way you usually move around.