[yupper32]

Nothing is missing. They're just burning fewer calories as they age. I'm not saying that metabolism isn't a factor (and that changes with age), it's just not something that eating more x or less y is going to change in any meaningful way.

[eloff]

It can, through the second order effects you mentioned yourself. Eating more x or less y can definitely help you reduce your calorie intake without feeling hungry all the time.

[dllthomas]

What if x is amphetamines?