Fat and fiction: calorie for calorie, the thin gain more - and other weighty findings

Science News, Sept 1, 1990 by Peter L. Weiss

Fat and Fiction

That skinny friend who pigs out but never gains weight might be a rarer bird than you thought. Contrary to widespread belief, thin people typically gain weight with fewer calories than the obese, a recent nutritional study suggests. The likely reason for the difference lies in the type of new tissue added.

These and other recent findings challenge some popular notions about weight gain and dieting. New research also raises questions about hunger in the obese and offers evidence that high-protein diets may aid in weight loss.

Thin people gain primarily lean tissue, whereas people already overweight add mainly fat, notes endocrinologist Gilbert B. Forbes in the August AMERICAN JOURNAL OF CLINICAL NUTRITION. But it takes six times as many calories to add a pound of fat as to add a pound of lean, he says. Thus, for the same calorie intake, thin people will gain more.

Forbes, of the University of Rochester (N.Y.) School of Medicine and Dentistry, reanalyzed data from six previous weight-gain experiments conducted by his team and others between 1975 and 1989. The studies included a total of 34 men and 29 women ranging from adolescence to middle age. Eight of the women had recently "stabilized" from severe malnutrition due to anorexia nervosa, an eating disorder involving self-imposed starvation.

In all six experiments, researchers fed people more food than needed to maintain their initial body weight. From the collective results, Forbes plotted excess calories per gram of weight gain against initial body weight and against percentage of body fat. He found that people with greater weight or body fat required more calories to add each gram.

Thin people with obesity in the family should take note, says obesity specialist Theodore B. VanItallie, a professor emeritus with Columbia University College of Physicians and Surgeons in New York City. "If you were physically active and for some reason you changed [to a more sedentary life style], you might begin gaining weight and gaining it quite rapidly," he warns. However, barring those hereditary pitfalls, people who maintain a steady weight into their 30s "haven't got much to worry about," he says.

Although VanItallie calls Forbes' work "a very valuable insight," he and others question certain aspects of the analysis--in particular, the inclusion of anorexics. "The dice are somewhat loaded when you use people who are undernourished," he says.

Ethan A. H. Sims, a professor emeritus with the University of Vermont College of Medicine in Burlington, thinks Forbes also biased his analysis by leaving out studies of "lean, hungry" people. In his report, Forbes says he excluded data from any studies in which people consumed more than 12 excess calories per gram of weight gain. He told SCIENCE NEWS he chose that figure as a cutoff because it is the "energy cost" of gaining pure fat, the body's most energy-rich tissue. Thus, 12 calories would represent the maximum surplus a person needs to add a gram of weight. "If people report more than that, there's an error somewhere," Forbes says.

Sims, on the other hand, contends that for some "lean, hungry" types the ratio of calorie intake to weight gain can exceed this theoretical maximum. In his own nutrition experiments, Sims studied prisoners and medical students whom he fed excess calories. Some gained little weight despite overeating by large amounts, he says. In those cases, the body's known energy-wasting mechanisms dissipated the excess calories, Sims suspects. New research to explore whether "lean, hungry" people make more use than others of energy-wasting, or "futile," metabolic cycles has begun in several labs, Sims says.

Another popular but questionable scenario depicts dieters inevitably regaining lost weight as they fight a losing battle against built-in survival mechanisms. Indeed, numerous studies have shown that metabolic rate falls precipitously during a diet -- out of proportion to the amount of weight lost. The metabolic slowdown apparently represents the body's attempt to counteract the reduced intake--which it mistakes for impending starvation -- by using food more efficiently.

But can the dieter's metabolism rise again?

A report in the Aug. 8 JOURNAL OF THE AMERICAN MEDICAL ASSOCIATION indicates that after weight loss ends, metabolism rebounds to a level normal for the new weight. In a 48-week experiment at the University of Pennsylvania School of Medicine in Philadelphia, researchers divided 18 obese women into two groups. One group ate a weight-loss diet of 1,200 calories per day throughout the study. Women in the other group ate 1,200 calories per day except during weeks 2 through 17, when they followed an extremely low-calorie regimen of 420 calories per day. Ultimately, women in the two groups lost comparable amounts of weight.

During the first five weeks, both groups showed steep declines in metabolic rates, report Thomas A. Wadden and his co-workers. But by the end of the study, those rates had risen to within 10 percent of their original levels. Other studies have revealed a similar effect, but the Philadelphia researchers tracked metabolism more closely and over an unusually long time period, Wadden says.