If something like what you're describing is going on then our psychological ability to manage hunger hasn't changed at all. Other things have changed, which is my whole point.
When we gain weight, we understand we need to eat less to lose weight. But that obviously does not work for many many people.
I'm carrying excess fat right now. Abolishing capitalism or taxing soda (or whatever other social, political, or cultural changes you would make) won't get rid of that fat. It is commendable to work on the social causes of obesity. I frame it as an individual psychological issue because it is an individual experience. If it was a matter of finding "the right foods to eat and avoid" or any particular set of facts that could convey how to actually lose weight, then the problem would be solved.
In other words, you can't tell someone to be hungry. Or at least, that doesn't sell any books or diet plans.
I'm not even sure what those conditions are. Capitalism is easy to blame for everything because it creates choices, both good and bad ones. But some capitalist countries have an obesity problem and others far less so. Socialist Cuba is a lot more obese than most European countries.
So I don't know what causes it on an epidemiological level and I have no solutions to offer. I'm merely questioning a particlar diagnosis. Framing the problem in a way that helps you personally is fine of course, but it's not the same thing as finding the truth about what causes the obesity epidemic.
There are 1000's of things that can cause weight gain, but there is an obvious solution - CICO. But that obvious solution doesn't work for many people.
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I think the scientific study of obesity is full of meta-scientific problems that affect our reasoning on the subject.
- BMI is easy to measure, and predictive at a population level; but it is not as strongly predictive at an individual level when you control for things like activity level and body fat percentage.
- It is very hard for individuals to measure calories consumed and expended. It is also difficult to do this in scientific studies - it can be done, and it has been done well, but it took many years to take this problem seriously.
- Hunger is not one thing. Hunger is hard to measure. Hunger is hard to break into components. Hunger is hard to communicate about.
- - Hunger has multiple physical and psychological components - how would you even teach this in school? With physical sensations like smell and taste, or with emotional sensations like anger?
- - Hunger is a sensation generated deep within the body and the brain. There are no scientific units associated with hunger. You can't get a "hunger level" lab done at your endocrinologist.
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Occam's Razor is a powerful tool. It feels good to find a "simple" answer. People want to find "the" cause of the obesity epidemic, but there is not one single cause. I will repeat my recommendation for "The Hungry Brain" https://www.amazon.com/dp/B01LXT28ZE/ and add a recommendation for "Burn" https://www.amazon.com/dp/B08D8JYQD6/ .
There are many factors in the obesity epidemic and they all work on different people in different ways. Some of them tend to increase the calories in and some of them tend to decrease the calories out.
CI factors - affluence, advertisement, psychological conditioning, "You can have it all" attitude, more junk food (list not exhaustive)
CO factors - less walking in daily life, more people living in areas where it is hard to go outside in the daytime, more sedentary lifestyle overall (list not exhaustive)
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Your body does have a voice that says "you have enough fat", but it is a little voice, and modern foods are highly desirable and calorie dense. There is some evidence that processed sugar has a strong effect on your hunger setpoint as well. There is strong evidence that having access to a wide variety of highly desirable foods leads to overeating (The Cafeteria Diet)
