Willpower certainly is the problem for most people.
Why was this not a problem prior to 1980? It is not as if we switched from hunter and gatherer society straight into postmodern world in 1980. People back then drove cars and ate in restaurants, and look at the photos: they looked far healthier. The fattest US state of 1980 was still much less fat than the fittest US state of 2020.
Why the same people who have a willpower problem can tolerate their bratty teenagers, rise up at 5 am to go to work, pull through arduous work etc.? After all, you would expect them to lack willpower generally, not in just one specific domain.
Humans are the same as they were. What changed is the amount of processed food and especially sugar in our diets. A lot.
People take in more calories today than in 1980, primarily through prepared foods. The guy in this blog post said he eats out for every meal. Basically no one but the super rich did that in 1980. Prepared food prices have fallen a lot since 1980.
Calories in/calories out is the only way that the human body can change mass, short of excision. However, it’s very hard to accurately keep track of calories.
Are people more fat today because they are less active, or are they less active because they are fatter? After all, it is no joy to move around with 30 or 50 lbs of extra fat. There seems to be a vicious cycle at work.
"Calories in/calories out is the only way that the human body can change mass"
True, but unproductive when it comes to understanding the phenomenon of rising obesity. WHY people consume more calories? What drives them? This is not a trivial question and without being fairly sure about the answer, we will not solve the situation.
An analogy: the only way that humans become alcoholics is by drinking a lot of alcohol. But that does not explain root causes of alcoholism, it is only a relatively trivial observation of the proximate cause. The reasons why some people can't keep their alcohol intake within harmless amounts and slide all the way to the bottom are anything but trivial.
They looked thinner, but afaik we are healthier all in all. Thin and healthy are not synonyms.
But diabetes 2nd type or chronic non-alcoholic steatosis were much, much rarer than today in < 50 population. Orders of magnitude rarer.
This is a significant disease load.
It just does not. If you focus on that only, it leads to diet that makes you feel like crap all the time. It makes you low energy, so you struggle or flat cant maintain performance and precision in work. It makes you irritable and it makes it much harder for you to handle normal stresses - meaning your kids and wife and coworkers basically suffer.
And what it does is that people eventually decide it is not worth it.
Is that true or just an artifact of screening? Hyperinsulinemia is not really well researched in "normal" population, because measurement of insulin in blood is not trivial; there are no simple devices similar to glucometers that could easily and affordably measure your current insulin level.
Eating a modern diet laced with hidden sugar is a surefire way to increase your total insulin level.
It is not as if a healthy pancreas has a choice. It automatically releases insulin as a response to certain stimuli, including sugar, but also interestingly protein. Only pure fat is "invisible" to pancreas AFAIK.
Too many people are still in thrall of the calories in - calories out principle.
It seems to appeal especially to nerds, the idea of reducing something as complex as metabolism into a simple accounting trick is just too attractive, and so is the idea that only "unused, extra energy" gets converted to body fat and that everything is question of raw willpower.
It is not so simple, if you live in a state of chronic hyperinsulinemia, you won't be able to mobilize stored fat, it is just biochemically impossible, adipose cells just will not release any stored fat if insulin is high. Of course, then you start to be hungry, then you eat some 'extra' calories even though you have ample fat reserves.
But the core of the problem isn't willpower. It is inability of the human body to burn its own fat for consumption if insulin levels are chronically high.
Of course, that leads to weight gain. And one of the main culprits is sugar. Excessive amounts of sugar will mess with your insulin secretion and sensitivity.