Forget the diet, the genes will fight you every step?

Science is always on the prowl for genetic explanations for common social ills, whether it be obesity, misbehavior, or disease incidence. So it should come as no surprise that your expected body mass is largely determined by your genes. The conclusive study of adopted children (whose birth parents are idenitified in documents) was published in the New England Journal of Medicine in 1986:

“The two major findings of this study were that there was a clear relation between the body-mass index of biologic parents and the weight class of adoptees...and that there was no relation between the body-mass index of adoptive parents and the weight class of adoptees..."

In other words, being fat was an inherited condition...

Dr. Stunkard also pointed out the implications..."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."

The science behind the finding is fascinating. In the late 1950s, a scientist at Rockefeller University wanted to study the differences in fat cells between obese and normal-weight folks. He gathered overweight volunteers and enforced a strict weight loss (often up to 100 pounds). By the end, the volunteers' fat cells appeared normal and the hypothesis was that they would leave permanently thinner. Not so:

Instead, Dr. Hirsch says, “they all regained”...Maybe, he thought, they had some deep-seated psychological need to be fat. So Dr. Hirsch and his colleagues, including Dr. Rudolph L. Leibel, who is now at Columbia University, repeated the experiment and repeated it again. Every time the result was the same....and 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.

...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.

The study left the scientists with an interesting question. If obese individuals were unable to reduce their weight because of their body's natural regulation, would folks who became fat be subject to the same restriction?

His subjects were prisoners at a nearby state prison who volunteered to gain weight. With great difficulty, they succeeded, increasing their weight by 20 percent to 25 percent. But it took them four to six months, eating as much as they could every day. Some consumed 10,000 calories a day, an amount so incredible that it would be hard to believe, were it not for the fact that there were attendants present at each meal who dutifully recorded everything the men ate.

Once the men were fat, their metabolisms increased by 50 percent. They needed more than 2,700 calories per square meter of their body surface to stay fat but needed just 1,800 calories per square meter to maintain their normal weight.

When the study ended, the prisoners had no trouble losing weight. Within months, they were back to normal and effortlessly stayed there.

In other words, not only is weight primarily genetically predetermined, but the body's natural metabolism fights to keep it within a that narrow, predetermined range. Fat people are literally starving themselves to remain thin, and thin people must literally gorge to gain weight.

However, given this evidence, how do explain this trend in weight gain in America?


What behavioral or environmental factors have overcome the natural mechanism for weight control? The best theory I've seen so far pegs sweetened beverages as the major factor, due to their low satiety (they don't make you feel full - link forthcoming). A cross-sectional review of clinical studies found that while additional study is merited, there's sufficient evidence that sugar-sweetened beverages contribute to obesity.

Consumption of [sugar-sweetened carbonated] beverages was shown to increase by 135% between 1977 and 2001. ¹⁵ It is estimated that, during this time, daily caloric sweetener consumption in the United States increased by 83 kcal per person, of which 54 kcal/d is from soda. ¹⁰

So find your body's optimal weight - kick the can!