Healthy is a nebulous term, but most of the goals humans have e.g living long enough to meet your grandkids, or perform cognitively well enough to earn a living

Healthy is a nebulous term, but most of the goals humans have e.g living long enough to meet your grandkids, or perform cognitively well enough to earn a living, implicitly include the instrumental goals of staying lean, and using your muscles regularly and vigorously. This is uncontroversial among scientists, and only called into question in the media. No one is quite sure why obesity has become such a problem, but I'll give you several hypotheses all with reasonable mechanisms, and each with at least some data for you to argue about. All of these things have changed in the last 100 years. - Base metabolic rates have declined. We burn fewer calories doing nothing. Body temperatures are lower. No one is sure of the cause, it might be downstream from one of these other ones. - We are more sedentary. - Antibiotics have caused extinction of gut microbes, which were previously endemic, and passed through the maternal line. - We take seeds, heat them up to extract oil, and put that oil in pretty much everything. This has significantly shifted the kind of fat in the food supply.