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

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.

The final metabolic rates, although reduced from original rates, simply reflected the smaller body size of the dieters, he explains. Just as "a smaller house will burn less fuel to heat it," Wadden says, from now on these women will have to eat less than they once did if they wish to maintain the new, lighter weight.

All of the women in the study increased their physical activity while dieting, mainly by walking more. The researchers suggest that the return to a metabolic level consistent with body weight may depend in some way on exercise.

One new report focuses specifically on the relationship between exercise and obesity. Aware that rats show appetite suppression for a short time after strenuous exercise, Harry R. Kissileff, F. Xavier Pi-Sunyer and their colleagues wondered whether the same pattern exists in humans. To find out, they compared the food intake of nine obese and nine nonobese women who ate after moderate and strenuous workouts.

In the August AMERICAN JOURNAL OF CLINICAL NUTRITION, they report that nonobese women ate more after moderate workouts than after strenuous exercise, but obese women consumed the same amount in each instance. The researchers suggest that this lack of appetite suppression reflects a peculiar unresponsiveness of the obese. Earlier studies have indicated that eating habits of obese people do not always follow the changing energy demands of their bodies, note Kissileff and his colleagues at the Columbia University College of Physicians and Surgeons.

According to another paper in the same journal, high-protein diets can suppress appetite--at least in monkeys. By a feat of surreptious plumbing, a Baltimore research team bypassed finicky monkey noses and taste buds to feed four monkeys a dietary supplement containing 50 percent protein. Anticipating that the animals might change their eating habits when presented with the modified diet--and thus throw a primate-wrench into the experiment -- the scientists implanted tubes into the monkeys' stomachs and connected them to food-delivery pumps. The monkeys, trained to feed at nozzles connected to other suction-activated pumps, unknowingly triggered both pumps with each oral feeding, thus getting a measured double-dose of food.

The protein-boosted diet caused the monkeys to eat less overall, dropping their total calorie intake by 25 percent, report Judy S. Hannah, Anil K. Dubey and Barbara C. Hansen of the University of Maryland School of Medicine. The finding, they say, adds to the body of evidence suggesting that high-protein diets can aid in weight reduction.

"A high-protein diet does appear to have an appetite-suppressing effect, and of course, if you want to lose weight, that could be beneficial," Hannah says. She warns, however, that people with kidney problems, high blood pressure or diabetes should not undertake a high-protein diet on their own. "In fact, anyone should always consult a physician before making major dietary changes."