> 50 years into an unexplained epidemic of obesity and metabolic disease that nobody has a clear explanation for,

I think you need to look at how the food has changed in this time. For example, here in the UK supermarkets dont want pigs with 1 1/2" of back fat so the farmer get the nutritionist to make up a diet low in vitamin B5 because it helps to shift the fat under the skin. Nett result, you have fatty organs and marbleized meat as the fat remains else where in the body. We can grow chickens in half the time it took to grow them in the 70's, chemicals in the environment remain in the body for years even lifetimes, pollution levels are at their highest in a generation, people dont exercise like they used to.