Why dieting makes you fat: Part I study
In a classic study, reported in the January 1986 issue of the Smithsonion, two obesity researchers from Rockefeller University in New York City observed a group of people who belonged to Overeaters Anonymous. All were of normal weight, but each had formerly been very obese. Although they all looked normal, their body chemistries were deranged. Their fat cells were tiny, similar to those in people with anorexia nervosa. Their pulse rate and blood pressures were low. They were always cold, and they burned about 25 percent fewer calories than would be expected on the basis of their weights and heights. Their biochemistry resembled that of people who were starving, and so did their psychology. They were always thinking about food.
A case history of one such person was given in the article. For a decade she had been losing and regaining weight. Finally she lost 100 pounds to reach her goal weight of 137 pounds. But the years of yo-yo dieting had taken their toll. She maintained her weight on 1,200 calories a day – approximately three fourths the calories that are needed to maintain a weight of 137 pounds in a woman whose metabolism is functioning normally.
What happens when we diet?
Dieting is commonly understood to mean lowering caloric intake below the amount necessary to maintain normal body weight. Such caloric restriction is interpreted by the body as starvation; so that it then takes steps to protect its energy stores. The body seeks to maintain a homeostatic balance between input and output; therefore, the lower the intake of calories, the lower the expenditure of energy. When dieters seek to resume a sustainable diet, they gain weight on calorie consumption that, in people whose metabolism is functioning normally, would maintain their weight. The more a person diets, the slower the metabolism becomes and the harder it becomes to shed weight.
A study with lab rats
Dr. Kelly D. Brownell of the University of Pennsylvania School of Medicine did a study with laboratory rats who were made to simulate a human yo-yo pattern of dieting by alternately gaining and losing weight. The first time the rats became obese and then were put on a diet, it took them 21 days to lose the weight they had gained and then 46 days to eat themselves fat again. But the second time they were put on the same diet, it took 45 days to return to their original weight – but only 14 days to regain what they had lost. That is, it took them twice as long to lose the weight the second time, and only a third as long to gain it all back again the second time. Regaining weight after dieting is not psychological but physiological.
In next week’s article, I will report on an experiment done with humans that corroborated Kelly Brownell’s experiment with lab rats. The response of the humans was exactly the same as the response of the rats.
Mary Lou Williams, M. Ed., is a lecturer and writer in the field of nutrition. She welcomes inquiries. She can be reached at 267-6480.