Not on mobile for once, so I'd like to give my 2 cents.
Any posts that claim we know for certain what the cause of mass obesity in the United States and increasingly the world aren't helping anyone. We don't know for sure - at least Scientifically. It's a poorly conducted field of Science that often violates the Scientific Method. It's hard to test as proper peer reviewed, double blind placebo studies would require long term locking up of humans for experimentation.
Personally I see the Food Reward Hypothesis of Obesity as the most compelling. These posts give an overview:
The Case for the Food Reward Hypothesis of Obesity, Part I
The Case for the Food Reward Hypothesis of Obesity, Part II
Food Reward: a Dominant Factor in Obesity, Part III
I think the author removed some of his posts because he recently wrote a book, but his older presentation overview is still around in
video form.
I believe it is most compelling because it explains the success of all diets I've seen, and it passes a sanity check.
Basically to make a recipe high reward you take any existing recipe and ensure that it has copious amounts of all of these:
1. Salt
2. Oil
3. Sugar, or at least sweetness
4. Pleasing texture, temperature, crunchiness
5. Meat or glutamate
This passes the sanity check because:
1. We as mammals, at least non opportunistic scavenger types, need to have some sort of complex instinctual reinforcement of sustenance without overindulging. Natural selection should have refined this to a nice equilibrium over millennia, at least with foods existing until modern humanity.
2. When was the last time you overate bland foods missing most of the 5 vs overeating foods that met most of the 5 rewards? How frequently?
Any explanation should cover all diets and causes.
Vegans may clamor that they are often thin. Yes, you all are. Probably because good cooking with your food ingredients to hit the 5 criteria is likely exceptionally rare within the United States. Try eating good Indian food, like Vegetable Pakora, and see how your appetite responds.
Paleo diets have success because they remove a lot of modern flavor enhancers and reduce sugar. Low carb diets similarly.
But to brute force calorie counting clearly doesn't work. Most people want to live longer, be healthier, etc, but when surrounded by an existing culture and food options are much more likely to succumb to hunger. There aren't suddenly hundreds of millions of special snowflakes in the US and abroad that have the conflicted opinion of being healthier but instead overeat anyway; we're all humans with the same genes - or more directly any multi-generational US citizens look at family photos from 1940 and earlier...95% of people are thin. Considering rodent and a few human studies show hunger (emphasis being not high level calorie spreadsheets) can be manipulated by food reward, then I think this hypothesis is worth looking into. Or ignore it - while the US is the leader in obesity we're also the leader in cheerleading brute force solutions; and spoiler alert they fail with better odds against you than Las Vegas.
Could I be wrong? Absolutely. The beauty of Science is self correcting based on data.