You don't eat only for energy, you also eat for nutrients - and they are a lot more varied and complex than the standard list of protein, carbs, fat, vitamins.
To use an extreme example so that it's easier to relate to: You can eat only sugar and nothing else and far exceed your energy requirements, but you will still have lots of appetite despite already having eaten too much in just energy.
Food composition matters - and optimizing for energy (counting calories) is a losing battle. Of course, this also requires that people have had experience with various foods. Kids grown on mostly just fast food, pizza and coke probably won't be able to develop healthy habits no matter what.
Yes it is technically possible to force a body to remain slim by counting calories. It also is either very cruel or, if you manage it on your own, requires an absurd amount of discipline to constantly battle your desires. Yes some people have a huge appetite for the obviously wrong kinds of foods, like more pizza and more ice cream and no water please because it "does not have taste" but coke or some other industry-made drink. When the body was "mis-trained" it can't magically desire the right stuff that it never learned about. The environment matters too, it's probably a lot easier to not eat terribly in Japan than in some US mid-west town.
I know eating healthy food for non-caloric nutrients is important. But don't most people already eat at least some healthy food? Couldn't most obese people get back to a healthy weight just by cutting out junk food, without adding any more healthy food to replace it?
They're usually poor and the junk food is subsidized. The us has underground cheese bunkers to keep the dairy industry running, you won't be seeing a nutritionally complete tempeh salad on the dollar menu.
I had some unfortunate experience with heavy metal poisoning (university clinic diagnosed - mercury, shown by lab tests). There was zero danger of dying and I doubt it took away any of my life expectancy. But it SUCKS and especially the brain works at a substantially lower level. I did not understand even simple sentences even after reading them several times at the height of the problem. I wrote Internet comments that made no sense when I read them again the next day, but at the time it felt perfectly alright and logical (sentence structure was weird too).
(Just an aside) And you know what? I had to end up with a senior researcher doctor at a university clinic before getting diagnosed. Because most doctors were a little like your question: They looked at the vitals and found no obvious disease and sent me home "it's all in your head". Which is funny because it's largely true - mercury being a neurotoxin, but for some reason the brain being the product of physics and bio-chemistry not registering with the oh so "science and evidence" based doctors, who seem to have a strangely meta-physical and esoteric view of it.
Anyway, back on topic:
I find this obsession with the binary outcome "death / no death" strange. Before death, your extremely parallel structure (not just your own trillions cells, each cell itself has lots of independently working parts, and then there are even more bacteria and other organisms occupying your insides and the outside who all contribute and are often affected too) does a poorer job of bringing the "you" into being. See your body like a computer running the software that is "you". The quality of the simulation drops if the hardware is impacted (you are the activity of your parts - a brain without activity is not "you", you are not there if the hardware does not run the "you" software). But the life expectancy may not be impacted at all.
Surely, if you provide far from optimal fuel you can expect the quality to suffer too, not just when you are poisoned or otherwise restricted.
So, it is a question of what version of "you" do you want to be? Is mere existence enough?
To use an extreme example so that it's easier to relate to: You can eat only sugar and nothing else and far exceed your energy requirements, but you will still have lots of appetite despite already having eaten too much in just energy.
Food composition matters - and optimizing for energy (counting calories) is a losing battle. Of course, this also requires that people have had experience with various foods. Kids grown on mostly just fast food, pizza and coke probably won't be able to develop healthy habits no matter what.
Yes it is technically possible to force a body to remain slim by counting calories. It also is either very cruel or, if you manage it on your own, requires an absurd amount of discipline to constantly battle your desires. Yes some people have a huge appetite for the obviously wrong kinds of foods, like more pizza and more ice cream and no water please because it "does not have taste" but coke or some other industry-made drink. When the body was "mis-trained" it can't magically desire the right stuff that it never learned about. The environment matters too, it's probably a lot easier to not eat terribly in Japan than in some US mid-west town.