Given the increasing attention to obesity in America — which is either a major public-policy challenge or a moral panic, or both, depending on your point of view — I’ve been reading up on the science behind it all. So I was totally into this awesome piece in today’s Science section of the New York Times, in which Gina Kolata surveys the four-decade-long work of the research physicians Rudolph Liebel and Jules Hirsch (pictured above, in his Times snapshot).

They did some incredibly hard-core experiments to explore the reasons people got so fat. In one study, they took a bunch of obese people who agreed to live at Rockefeller University Hospital for eight months — dieting carefully to bring their weight down by about 100 pounds each. It worked, and when they examined the patients’ fat cells, the scientists saw that the cells had transformed: They used to be huge and stuffed with yellow fat, and now were normal in size. But they all regained their weight later on. As Kolata reports:

[That] led them to a surprising conclusion: fat people who lost large amounts of weight might look like someone who was never fat, but they were very different. In fact, by every metabolic measurement, they seemed like people who were starving.

Before the diet began, the fat subjects’ metabolism was normal — the number of calories burned per square meter of body surface was no different from that of people who had never been fat. But when they lost weight, they were burning as much as 24 percent fewer calories per square meter of their surface area than the calories consumed by those who were naturally thin.

The Rockefeller subjects also had a psychiatric syndrome, called semi-starvation neurosis, which had been noticed before in people of normal weight who had been starved. They dreamed of food, they fantasized about food or about breaking their diet. They were anxious and depressed; some had thoughts of suicide. They secreted food in their rooms. And they binged.

The Rockefeller researchers explained their observations in one of their papers: “It is entirely possible that weight reduction, instead of resulting in a normal state for obese patients, results in an abnormal state resembling that of starved nonobese individuals.”

In a reversal of this study, Ethan Sims of the University of Vermont took a bunch of naturally slender people and had them eat up to 10,000 calories a day, until they became obese. They had no trouble losing the weight and keeping it off. In a later study, Hirsch and Liebel examined children who’d been adopted and found that their adult propensity for obesity — or thinness — closely tracked their biological parents. If their biological parents were obese, it didn’t matter if the kids grew up with skinny parents who taught them healthy eating patterns; they most often wound up obese too.

The public-policy implications, the scientists argue, are significant. If it’s true that the children of obese parents are the ones most likely to become obese — “80 percent of the offspring of two obese parents become obese, as compared with no more than 14 percent of the offspring of two parents of normal weight” — then it’s waste of money to target the anti-obesity message at the children of skinny folk. One could do more to fight obesity by devoting resources to locating and supporting those most at risk.

Mind you, given that being fat carries such a powerful social stigma, one might wonder about the emotional ramifications of a nation-wide effort to round up all the fat kids and target them with weight-control programs. Either way, this question of the genetic basis of obesity is really interesting, and I now want to read Kolata’s book Rethinking Thin: The New Science of Weight Loss — and the Myths and Realities of Dieting