You're right and wrong. Many obese people have done this and lost weight... and then gained it right back again. Over, and over again.
There is a persistent myth that the obese person lacks some spiritual strength or willpower. I think your comment implies this.
And yet they do have the willpower to lose weight? And something happened in 1980 which turned 30% of adults into weak-willed moral degenerates, and more and more every year? Is that actually plausible in an era with unsurpassed interest in healthy eating, where people voluntarily exercise more than they ever have, with better quality food than we have ever had?
The original researchers who suggested a mass trial of the potato diet over social media aptly said "the study of obesity is the study of mysteries". They're investigating some high-risk hypotheses that chemical contaminants are the cause of skyrocketing obesity. Worth a read.
> People in the 1800s did have diets that were very different from ours. But by conventional wisdom, their diets were worse, not better. They ate more bread and almost four times more butter than we do today. They also consumed more cream, milk, and lard. This seems closely related to observations like the French Paradox — the French eat a lot of fatty cheese and butter, so why aren’t they fatter and sicker?
https://slimemoldtimemold.com/2021/07/07/a-chemical-hunger-p...