The impetus for this study was to better understand exactly what happens to the body during weight gain. For instance, do fat cells increase in number or simply grow larger? At first, the scientists sought volunteers from a usually reliable source of guinea pigs: graduate and medical students at the college. But the study design, which required the volunteers to eat four large meals a day at the nutrition lab, proved far too time-consuming for busy students. So the researchers turned to a more captive crowd: inmates at the Vermont State Prison. They hired a cook to prepare the meals and served the food on china plates instead of tin. The prisoner’s ample diets included standard American fare: cereal, eggs, and toast for breakfast, sandwiches for lunch, and dinners of meat, potatoes, and vegetables. The fourth meal, which the men ate just before bedtime, was similar to breakfast.
The volunteers started out at normal weights, which ranged from about 135 to 185 pounds. During the ten-week-long study, the men managed to gain between 15% and 25% of their body weight, which amounted to an average of nearly 36 pounds. To do so, they had to eat 8,000 to 10,000 calories a day—more than three times the normal number of calories they would have needed to maintain their weight. The weight changes were largely due to gains in body fat. By taking small samples of fat from the men’s bellies, thighs, and arms before and after the overfeeding, the researchers demonstrated that this excess fat didn’t create new fat cells but rather expanded the existing ones.
This study and similar ones on the prisoners revealed other interesting phenomena related to body weight and the set point. Researchers found that the prisoner’s metabolic rates went into overdrive after the overfeeding period. These changes provide further evidence of the body’s drive to restore balance and return to its set point. When the experiment ended and the men went back to eating regular amounts of food, they lost weight quite quickly—not just because they were eating less but because their metabolic rates were still racing. Note that the prisoners did not remain at the new, higher weights for very long, so they did not reset their set points to new, higher levels. That contrasts with people who have been overweight for long periods of time.
The rapid weight loss these prisoners experienced is the mirror image of what happens when overweight people try to lose weight. If your set point is too high and you try to lose weight quickly, your body will fight to defend that weight and slow down your metabolism. But if your set point is within a normal range, your metabolism will speed up when you gain weight quickly.
In recent years, many studies have reaffirmed the observations from these historic reports. One pivotal 1995 study, by Jules Hirsch and colleagues at the Rockefeller University in New York City, used sophisticated techniques to carefully measure the metabolic rates of forty-one obese and nonobese volunteers who followed strict diets that caused them to either lose or gain 10% of their body weight. The researchers found that when people gained 10% of their usual weight, their bodies focused less on conserving energy and more on wasting it. But when people lost more than 10% of their usual weight, the opposite occurred: their bodies fought to save energy rather than expend it. This explains why it’s so difficult to lose more than 10% of your weight at a time.
So no matter where you start (overweight, thin, or somewhere in between) and no matter how you manipulate your diet (eating too much or too little), your metabolic rate will automatically adjust in an effort to keep you at the same set point.
Source: George L. Blackburn, M.D., Ph.D., "Break Through Your Set Point: How to Finally Lose the Weight You Want and Keep It Off," 2008