Metabolism

You're confusing metabolism with hunger. While the two are largely correlated, there is not necessarily a strictly causal relationship. Hunger can occur in the absence of metabolic need due to hormonal signals, environmental cues (such as the smell of food) or psychological cues (social settings, habits). There can be both genetic and environmental factors at hand.

I've noticed eating more doesn't seem to delay the time period till being hungry the next time by all that much. Especially with anything containing sugar that seems to create more appetite. I usually aim to eat just enough to not be hungry.

We've got refrigerators now! Storing lots of energy can be a machines job!, eating a lot seems like the ultimate in not taking advantage of modern tech.

I've seen a study saying people who exercise regularly are better at automatically (subconsciously?) moderating intake to match expenditure. And I believe some foods, like fructose based drinks, don't satiate despite the calories they provide.

Likely age-related. Your metabolism slows down as you age.

https://www.piedmont.org/living-better/why-metabolism-slows-...

I'm not an expert, but I've discovered there are a number of factors.

We are complex chemical reactions, and our diet, our (gut) bacteria and any viruses, all three of which will affect us, so some of it will be biological, ie chemical response, some of it will be bacterial in and out of the gut, and some could be viral.

Rabies is a virus that creates hydrophobia, an aversion to water, now if someone could create a virus that creates an aversion to food, they would be rich!

Chemicals can also alter what you want to eat, like craving fatty foods or sweet foods, some of which is purely for your bodies needs, and some cravings will be stimulated in part by bacteria.

As will the amounts eaten.

The thing to bear in mind is, even if eating traditional foods, ie home grown meat and veg, the soil type becomes a factor on the size of the food grown beit livestock or veg, as does the environmental factors like the reduction in sulphate aerosols which were contributing to global dimming.

Now the sulphate levels have been reduced, we can now start to see the sunshine reaching the surface of the planet a bit more so we can have warmer soil and sea temperatures aka climate change. That then helps livestock and plant growth provided its not too hot or drought like. Better veg naturally grown without manmade chemicals can be healthier, more nutrient dense.

If you go back even further in Earths history, the concentration of minerals on the land have changed, for example manganese on the land was much much higher some suggest as much as 17% of sample, than it is today because its largely been washed off the land over millennia.

So how much has the human body also evolved? Keeping bacteria down seems to be key though for a longer healthier life as is getting the right chemical intake.