it would be pretty surprising to find that, say, propionate intake suppressing intestinal yeast growth was a major cause of the obesity pandemic. but it certainly seems to be something about industrial food manufacturing that goes beyond just caloric density and macronutrient balance, and additives seem like a promising place to look
i mean the village baker a century ago didn't put calcium propionate in his bread so it wouldn't get moldy, he just threw the moldy bread out
As an example, let’s say you go from a healthy adult at 18 years old and 160 lbs, to an obese adult at 40 and 300 pounds. That’s 140 pounds over 22 years. If a pound of weight is gained after 3,500 excess calories, then this person only consumed roughly 60 extra calories a day. If they consumed only 20 excess calories a day, they would be 195. Overweight, but still relatively healthy. It doesn’t take a lot of sugar to add 40 or 60 calories to someone’s diet and leave everything else unchanged.
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.