The CDC had already established that the obesity epidemic actually seems to spread from person to person, exactly like a disease as far as the epidemiology was concerned, but had no explanation as to why it would act this way. Some studies subsequent to that found that many fat people seemed to have different populations of gut bugs than thin people, and that the gut bugs in fat people were more efficient at converting food into digestible calories.
Another groundbreaking study in Scandinavia found that people's lifetime baseline metabolism was determined in the womb (comparing WW-II era babies that were carried to term during famine with normal babies born before and after the famine years). Other species also seem to do this, an evolutionary method of tuning offspring to their future environment's energy availability. During the Korean War American POWs were literally starving to death while being fed better than their North Korean guards, whose low-metabolic energy requirements were adapted to extremely low calorie intakes.
So given all that, this study is not that unexpected. We had once proved
that ulcers were caused by stress and diet - until it was proved to be caused by a bacteria called Heliobactor pylori
, overturning the conventional medical wisdom.
Back in the 1900's, and the 1950's, and the 1960's, people didn't spend their time jogging and going to the weight room, or paying for personal trainers, or buying rooms full of exercise equipment like stationary bikes and treadmills. They also ate high-fat, high-calorie diets (steak and potatoes, potatoes and steak, bacon and eggs with a side of meatloaf). Even the breeds of meat were high fat, with everyone wanting beef and pork with lots of marbleing. Diet foods, which now fill whole aisles of the supermarket, were virtually unheard of. They still didn't get fat in the numbers we have now.
What did happen since the 1950's is that everyone in the West, but especially America, started being given high-dose antibiotics for just about everything, even colds and flu. Anti-biotics can severely impact gut-bug populations, drastically shifting the equilibrium, often wiping almost all of them out, making the gut available for re-population by opportunistic strains picked up from friends and family - who, if they are fat, would be much more likely to carry either the fat-inducing gut bugs or the more efficient calorie-scavenging gut bugs.
And under no currently accepted understandings could gastric bypass surgery cure diabetes in two or three days, yet it seems to be doing so in what, about 80% of cases? One day we may look back on the total diet and exercise view of obesity as being as primitive and silly as blaming epidemics on people's sinful ways and their rejection of God. Future studies will see whether this is, in fact, the case.