Earlier quoted context omitted.
Just speaking from personal experience, I’m fat because I eat cake and ice cream every day and walk 6,000 steps on a good day. I don’t really see a mystery here tbh.
The prevalence of sugar in modern diets along with how ludicrously industrialized food has become, particularly in America, is likely still the main cause for obesity rates. People point out all these other secondary factors but we should really focus on the 80%, the big ticket item. It's damn near impossible to find nutritiously acceptable breakfast, lunch and dinner choices near the office in big cities in America.…
However, I can't find trustworthy original academic research on it, which makes it difficult to draw any firm conclusions. In any case, it doesn't appear that sugar consumption has risen dramatically in the last 50 years in the UK, yet obesity rates (and associated metabolic diseases) have continued to rise. Most research seems to suggest sugar is a marker of an unhealthy lifestyle rather than the cause, but the cause still seems to be essentially unknown. It is true that countries that eat very little sugar tend to have lower obesity rates, but that seems mainly to be because they are usually extremely poor.
In my opinion, there's more evidence that low fibre and easily digestible food is a bigger culprit than sugar, but the evidence is very poor quality on all sides.