Experiments seeking to produce weight loss are a dime a dozen these days. In the midst of a burgeoning obesity epidemic, there is no shortage of dietary solutions demanding to be studied.

But fifty years ago, as obesity was beginning to crop up on researchers' radar, a study of a different sort helped to radically alter prevailing scientific views on the matter.

Experts today recognize that chronic obesity is a nuanced health issue influenced by behavioral, genetic, physiological, and cultural factors. In the 1960s, however, conventional knowledge held that obesity was a simple problem of laziness.

George A. Bray, a University Professor emeritus in endocrinology at Louisiana State University, dedicated his half-century career to studying obesity. He summarized the archaic views of decades ago (some of which persist in the general population today) in a recent article.

"Indeed, obesity was viewed as a 'lack of will power' and many people thought, and some said, if only these patients would push themselves away from the table they wouldn’t have this problem. It was their fault!"

What started to alter that opinion was a seminal study published in 1971. This was not an experiment that assigned overweight individuals to a weight loss diet, but one that instead challenged normal weight individuals to put on lots of pounds. The subjects were inmates of the Vermont State Prison, granted reduced sentences for volunteering (a practice considered unethical today). For half a year, their diets were meticulously managed, first to ascertain their baseline weights, then to cause them to gain a lot of weight, then to return them to their baseline weights. All the while, the researchers scrutinized what was going on inside the inmates' bodies.

During the weight gain phase, the inmates did indeed bulk up considerably, mostly via an increase in fat. Eating as many as 10,000 calories per day, they ballooned in weight by an average of 20.9%, roughly 35 pounds each!

Remarkably, however, just ten weeks after returning to normal diets, every single subject returned to their previous size.

"This clearly contrasts with the difficulty people with spontaneous obesity have in losing weight," Bray noted. "For most of them it is a lifelong struggle."

The takeaway was that some people simply aren't physiologically predisposed to being overweight. Our bodies have a size and shape that they are inclined to maintain. A big clue to this finding was that subjects' adipocytes – fat cells – did not increase in number but rather grew in size. The Vermont inmate study provided the first clue to what scientists now know: fat cells grow by soaking up energy in the form of liquids and this explains most weight gain. However, the number of fat cells in the human body is largely set by adolescence, and can only change with years of overeating or caloric restriction, perhaps on account of epigentic changes. This explains – at least partly – why losing weight is so incredibly difficult for chronically overweight individuals.

The Vermont inmate overfeeding study inspired a young Bray to focus his scientific career on exploring the metabolic reasons for obesity. Now 88, and retired (mostly), he can speak on the subject with an intellectual standing that few others can match.

"In my view, people do not consciously choose to have obesity; rather, the obesity “slips up” on them and once present is difficult to reverse," he says.

"Although there is much more to learn, the history of overfeeding and underfeeding trials and other lines of evidence clearly show that obesity prevention and treatment cannot simply rely on advice to eat less and move more."