More from "Rethinking Thin":
Could it be that the problem with obesity is that some people are just weak-willed at some point in their lives and allow themselves to gain unconscionable amounts of weight? One way to interpret Hirsch and Liebel's studies on the near impossibility of permanent weight loss for the massively obese would be to propose that once you get fat, your body adjusts, which makes it hopeless to lose weight and keep it off. Maybe if you let yourself get fat, you seal your fate: being obese becomes normal for your body. The question was important because if getting fat was the problem, there might be a solution to the obesity epidemic—convince people that any weight gain was a step toward an irreversible condition that they most definitely did not want to have.
But it turned out that the answer to that question was not what many had hoped.
That uncomfortable discovery began with studies in Vermont around the same time as Hirsch was doing his studies in New York and that continued into the 1980s as a few scientists probed further. The studies were done in different ways by different researchers and in different populations, but they all found the same thing. Yet perhaps because their results cast into question everything that is commonly believed about gaining weight, they have become known mainly to research scientists and ignored by the general public.
The first experiments were the inspiration of a scientist, Ethan Sims of the University of Vermont, who asked what would happen if thin people who had never had a weight problem deliberately got fat. This was, of course, the reverse of the famous Ancel Keys experiment, but that was not how or why Sims thought of it.
Sims says he got the idea from research he had done during a sabbatical year, when he was trying to make mice fat. That turned out to be difficult—even when they were supplied with abundant tasty food, the mice ate only enough to maintain their weight. Sims could force- feed the animals, but then they would increase their metabolic rate and burn more calories, which led them to gain less than was predicted. Even if the animals put on some weight, they would lose it and go right back to their original weights when the study ended. Sims began to wonder whether people, too, would have a hard time gaining weight. No one had ever really asked—who, after all, would want to get fat?
But Sims was a university faculty member, and when he returned to the University of Vermont he managed to find subjects for his weight-gain study among its students. He deliberately recruited students who had never been fat and had no family history of obesity and who were willing to make a serious effort to try to become fat. It sounded as if it would be easy—all you would have to do is indulge yourself with all of your favorite calorie-laden treats. Most people, when asked, say they could weigh much more than they do but that they exert their willpower to keep their weight down.
But Sims and his student volunteers found otherwise. To their own surprise, these subjects found it all but impossible to gain much weight; no matter how much they tried to eat, they just could not become obese. The experiment was a failure. Could it have been that deep down the students really did not want to be fat? Was it really that hard to gain weight?
Maybe, Sims decided, the problem was that the volunteers were free to move about and were burning too many calories with physical activity. He thought of the perfect subjects, people who really would have no chance to cheat and burn off calories: prisoners. So he repeated his experiment with men who were incarcerated in a nearby state prison and who volunteered to become fat.
This time, the experiment worked, in a fashion—the men got fat. But producing obesity turned out to be much harder than Sims had anticipated. The men increased their weight by 20 to 25 percent, but it took four to six months for them to do this, eating as much as they could every day. Some ended up eating 10,000 calories a day, an amount so incredible that it would be hard to believe, were it not for I he fact that the research study had attendants present at each meal who dutifully recorded everything the men ate.
But when Sims calculated the amount of weight the men should be gaining, he discovered that they were gaining much less than would have been predicted and that different men gained at different rates. Once the men were fat, Sims asked how many calories they needed to maintain their weight and how that compared with the calories they needed when they were at their normal weights, before the study began. The answer was astonishing: When the thin men got fat, their metabolism increased by 50 percent. They needed more than 2,700 calories per square meter of their body surface to stay at their obese weight, but just 1,800 calories per square meter to maintain their normal weight.
Maybe all fat people have very fast metabolisms, strange as that might seem. But no. Obese people who got that way naturally turned out to have perfectly normal metabolic rates, no different from the average metabolic rate of a thin person who is at a weight that feels comfortable and easy to maintain.
Then Sims did another study. He recruited very heavy men and dieted them down to the same level of fatness as the newly obese prisoners. These men, while just as fat as the prisoners, needed half as many calories to maintain their weight. That, of course, was just what Jules Hirsch had found, but the results helped convince Sims that his striking findings with the men who gained weight were correct. The men who lost weight were like the mirror image of the gainers.
As for the fat cells of the newly obese prisoners, it turned out that they had simply grown larger, much larger, but their number remained constant. The men were fat, but they got that way by stuffing the cells they already had with globules of fat, not by growing more fat cells. So, because they always had fewer fat cells than people who were naturally fat, they were fundamentally different from naturally fat people.
When the study ended, the prisoners had no trouble losing weight; within months, they were back to normal and effortlessly stayed there.
The implications were clear. There is a reason that fat people can't stay thin after they diet and that thin people can't stay fat when they force themselves to gain weight. The body's metabolism speeds up or slows down to keep weight within a narrow range. Gain weight and the metabolism can as much as double; lose weight and the metabolism can slow down to half its original speed. That, of course, was contrary to what every scientist had thought, and Sims knew it, as did Jules Hirsch.
In a review article published in 1976, Sims wrote, "Ever since Lavoisier demonstrated animal respiration, there has been a tendency to assume that animals constantly burn their substrates with the same even flame and the same even efficiency." But, he added, "there is no reason to believe that this maximum is achieved or is constant in different individuals under different conditions." Hirsch wrote his own summary of the work:
The body weight of an obese or nonobese person tends to remain constant. When the system for controlling fat storage is challenged by experimental over- or under-feeding, energy expenditure alters as a counter force, "bucking" the change. The overfed person increases fat storage but burns more calories, which acts as a brake on further accumulation of fat mass. The reverse occurs with weight reduction; a decline in body fat storage leads to a decrease in the burning of calories.
The message never really got out to the nation's dieters, but a few research scientists were intrigued and asked the next question about body weight: What determines whether someone will be fat or thin? Is body weight inherited? Or is obesity more of an inadvertent, almost unconscious response to a society where food is cheap and abundant and oh, so tempting? An extra 100 calories a day will pile on 10 pounds in a year, public health and obesity experts are fond of telling us. Keep it up for five years and you'll be 50 pounds heavier.
Of course, everyone has seen fat families—photos of fat parents with their fat children have become almost a cliche in today's obesity- obsessed nation. And everyone has seen families in which the parents are slender and all their children are thin. But there are two possibilities that could explain why the children of fat parents are fat: it could be that the children inherit a genetic tendency to be fat, or it could be that the parents encouraged bad eating habits and an abhorrence of exercise. Growing up in a household where gargantuan portions are the norm, or where the kitchen is always stocked with tempting chips and nuts, cookies and ice cream, might make anyone fat. Or so it would seem.
That is the assumption behind today's push to change the food offered in schools, getting rid of soda machines and replacing high- fat meals with ones with less fat. It is the assumption behind the movement to ban junk-food advertising that is directed at children. And it is the assumption behind the assertions that people today are fat because there are too few bike paths or sidewalks or because schools are not devoting enough time to physical education. The assumption is that your environment determines your weight.
Mickey Stunkard, ever the iconoclast, wondered if that assumption was true and, if so, to what extent. It was the early 1980s, long before obesity became what one social scientist calls a moral panic, but a time when those questions of nature-versus-nurture were very much on his mind.
Stunkard wanted to study adoptees—a classic method of deciding the relative contributions of genes and environment to human traits. But he needed large numbers of people who had been adopted in infancy and reared apart from their biological parents, and he needed to know the height and weight of the biological parents, the adoptive parents, and the adoptees.
Such information is not available in the United States, where adoption records generally are sealed and there is no national database of adoptions. But, by chance, Stunkard discovered what looked like a perfect way to address his questions— it turned out that there was an adoption registry in Denmark that should have all the information he needed.
The registry had been developed to study mental illnesses. It was instituted by Harvard psychiatrist Seymour Kety, who had worked with researchers in Denmark in his quest to understand whether schizophrenia was inherited and had used that country's meticulous medical records of every adoption there between 1927 and 1947, including the names of the adoptees' biological parents. But when Kety used the registry for his research study, the results were disappointing. Schizophrenia was so rare in that Danish population, occurring in just 0.5 percent of the people, that he could not conclusively establish whether a tendency to develop it was inherited or not.
Stunkard, however, saw an opportunity to answer his questions about obesity. One day, when he and Kety were talking about the registry, he popped the question. "I said, 'My goodness, do they have heights and weights [of the people in the registry]?' He said yes, they have heights and weights, but why would that matter?" Stunkard explained that he might be able to use the Danish registry to determine whether body weight is inherited. Kety agreed to write to the Danish psychiatrist Fini Schulzinger, who oversaw the registry, and with that introduction, Stunkard went to Copenhagen to meet with Schulzinger and beg to be allowed to use the data.
The visit was unsuccessful, Stunkard recalls. "Schulzinger said, 'Well, Dr. Stunkard, we are the psychiatric institute. All we deal with are psychiatric issues, and obesity is a somatic issue and we don't deal with that.'"
For five years, Stunkard pleaded with Schulzinger, but got no further. Finally, he gave up. He had learned of another adoption registry, in Iceland, and scientists there seemed eager to allow him to do his study. So he got a plane ticket to Iceland to meet with the geneticists there. It turned out that for the same price, he could continue on to Copenhagen after staying in Iceland. Why not? he thought, and made the arrangements.
"When I arrived in Copenhagen, Schulzinger said, 'I have someone to work with you.' I said, 'On what?' He said, 'On the adoption registry.'" Astonished, never understanding why Schulzinger had suddenly changed his mind, Stunkard leapt at the chance. What he thinks of as his five-year courtship of Schulzinger was over. He could finally get down to answering that nature-nurture question with rigorous and extensive data.
Stunkard's Danish collaborator turned out to be "a very, very young guy," Thorkild I. A. Sorensen, who had never published anything but who was enthusiastic and willing. The researchers did their analysis of the registry data and began writing a paper. "I would write a draft and mail it to him. Two months later, he would send it back to me with his comments," Stunkard says. "I think we spent three years writing that paper. Then we sent it to the New England Journal of Medicine. They took it right away."
And no wonder. The study included 540 adults whose average age was forty. They had been adopted when they were very young— 55 percent had been adopted in the first month of life, and 90 percent were adopted in the first year of life—and reared apart from their biological parents. The investigators divided the adoptees into four categories: thin, average weight, overweight, and obese. Then they mailed general health questionnaires to the adoptees' biological parents and their biological siblings, asking for, among other things, their height and weight.
The results, published in 1986, were unequivocal. The adoptees were of the same fatness as their biological parents, and their fatness had no relation to how fat their adoptive parents were.
The scientists summarized their data: "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, suggesting that genetic influences are important determinants of body fatness; and that there was no relation between the body-mass index of adoptive parents and the weight class of adoptees, suggesting that childhood family environment alone has little or no effect."
It did not matter what the children's adoptive parents fed them; it did not matter whether they set a good or a bad example with their diets and exercise habits. The fatness or thinness of children when they grew up had nothing to do with their adoptive parents. It had everything to do with the fatness or thinness of their biological parents, even though the children may have had no contact with their biological parents and may not even have known them.
In their paper, Stunkard and his collaborators pointed out the implications:
Current efforts to prevent obesity are directed toward all children (and their parents) almost indiscriminately. Yet if family environment alone has no role in obesity, efforts now directed toward persons with little genetic risk of the disorder could be refocused on the smaller number who are more vulnerable. Such persons can already be identified with some assurance: 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.
