Cathy entered the weight-loss program at the University of Pennsylvania Medical School with a warm personality, an infectious smile and a great desire to be thin.
My colleagues and I were beginning to experiment with a very low-calorie diet at our clinic, a fast combined with nutrition supplements that was designed to get rid of a lot of weight very quickly. The diet had just 420 calories per day.
Cathy did well on it initially, dropping from 230 to 193 pounds. Then she stopped losing weight. Something was wrong. A 193-pound person should certainly lose weight on 420 calories a day. Was she cheating on her diet? We did not believe so. Would more exercise help? She was already walking up to 3 miles a day.
Cathy was heartbroken. She wanted desperately to slim down: She felt it was important for her energy level, attractiveness, self-image and health. We wanted to help, but she was already on the strictest diet at our disposal. I began to wonder why Cathy's body was resisting weight loss. How could her body be so efficient, maintaining so much weight on so few calories?
Like most people in our clinic, Cathy had lost weight in the past, but she had regained it. My impression was that patients who had dieted many times in their lives had the most trouble losing weight in our program. At first glance, this seemed logical. Veteran dieters probably had some physiological disadvantage, such as a low metabolic rate--the rate at which their bodies use up energy from food and other sources. This made them gain weight in the first place, I thought, and then made it difficult for them to lose weight and keep it off.
Cathy, however, prompted me to take a different perspective. Was it possible that previous diets actually created this tendency to maintain more than 190 pounds on just a few calories? Could dieting inhibit later weight loss?
These questions generated a project now involving researchers from five universities who are focusing on "yo-yo dieting": repeated cycles of weight loss and gain. Many people diet this way, even those who are not overweight. We are examining the effect of yo-yo dieting on metabolism and health.
This dieting pattern stems from the tremendous cultural pressure to be thin: There are even alarming reports of parents who restrict their infant's food, hoping to prevent obesity later in life.
The connection between the weight-loss problems of people like Cathy and their history of repeated dieting cried out to be tested in a systematic way. But it's unethical to ask people to lose and regain a lot of weight repeatedly; it could be harmful. In addition, it would require many years to follow a group of human dieters long enough to see the natural consequences of yo-yo dieting. Our initial choice, then, was to look to the animal laboratory.
I enlisted the aid of Eliot Stellar, a physiological psychologist at the University of Pennsylvania; Marcie Greenwood, a biologist at Vassar College who ran one of the world's most productive labs for the study of obesity; and Eileen Shrager, a postdoctoral fellow in our lab.
We studied several groups of adult male rats, putting one group through an experience similar to human yo-yo dieting. These rats were put on a high-fat diet and became obese. Then they were placed on a balanced weight-loss diet until they returned to normal weight. After that, they were given free access to the high-fat food, and they regained their lost weight. This cycle was repeated so that our yo-yo dieters completed two cycles of loss and regain.
46 Days to Lose Excess
The results were striking. The yo-yo dieters needed 21 days to lose their excess weight during the first cycle. But after they regained this weight and started the second cycle, it took them 46 days to lose it again, even though their diet was exactly the same.
There was an even greater difference in the time it took the rats to put the weight back on. In the first cycle, the animals needed 45 days to return to their obese weight after they came off their diet. To regain the same weight in the second cycle took just 14 days. Weight loss was two times slower and regain was three times faster during the second round of yo-yo dieting than during the first round.
It appeared that our animals were responding to dieting by using food more efficiently. They gained more body weight per gram of food eaten, and so maintained their weight on fewer calories. This formed the cornerstone of our "cycling hypothesis." We thought that weight loss and regain enhanced the efficiency of food use and that weight would be lost more slowly and regained more rapidly with successive cycles.
Since the body needed fewer calories, the same number of calories that led to stable weight, or even weight loss, before dieting could produce a weight increase afterward. Weight cycling could actually contribute to obesity.
It was time to test our ideas on people. G. Terence Wilson, a psychologist at Rutgers University, and I began looking for people who had been through a dieting program more than once so we could evaluate their weight loss on successive diets. We found information about just such a group of dieters through George Blackburn, a physician at Harvard Medical School and the New England Deaconess Hospital. Blackburn and his colleagues were pioneers in the use of very low-calorie diets and had records of a large population of dieters who had been part of their outpatient program.
Support for Ideas
We collected details about 111 patients who had lost weight in Blackburn's clinic, had regained some or all of the weight and then enrolled in the clinic a second time. What we found supported our ideas about cycling: These patients had a slower rate of weight loss--2.1 pounds per week on their second diet, contrasted with 3.1 pounds per week on the first diet.
But we were uncertain whether we were seeing changes in physiology or whether it was just harder for patients to follow their diets the second time. To test this, we picked 49 patients who lost at least 2 pounds per week on both diets, since losing this much weight usually reflects strict dieting. Weight loss among this group of patients was still markedly lower on the second diet than on the first.
Later, we found this pattern also held true for a group of hospital inpatients whose food intake was carefully controlled and whom Blackburn had been testing on low-calorie diets. This gave us more confidence that the slower weight loss was metabolic and not from cheating.
Thus, the Weight Cycling Project was born. This 5-year study, paid for by the MacArthur Foundation, is 3 years old. Our team has expanded and consists of myself, Stellar, psychiatrist Albert Stunkard and psychologist Tom Wadden from the University of Pennsylvania, Greenwood from Vassar, Wilson from Rutgers, Blackburn and physician Leighton Read from Harvard and psychologist Judith Rodin from Yale University.
We span many disciplines, and our diverse viewpoints and skills have given rise to some exciting research ideas. By combining the abilities of our laboratories, we can conduct both basic and applied work, can study both people and animals and bring many perspectives to bear on weight cycling.
Body Composition Altered
It is possible that people who cycle on and off diets may eventually end up at a lower body weight than people who never diet. This happens, for instance, with female rats in our studies. However, Greenwood's lab found that yo-yo dieting altered the body composition of female rats so that such animals tended to have a higher percentage of body fat than animals that remained obese.
Even though animals that had been through several diet cycles weighed less than non-dieters, more of their weight consisted of fat, so they ended up with just as much body fat. This could be caused by increased activity of an enzyme called lipoprotein lipase in body tissues. LPL is considered the "gatekeeper" that determines how much fat is stored in fat cells. Repeated dieting could increase LPL activity in rats; if it also does this in people, dieters would be more efficient at storing fat and have more fat in their bodies.
Consider a hypothetical dieter, Christine, who drops from 140 pounds down to 120 pounds. She might lose 15 pounds of fat and 5 pounds of muscle. If she regains the 20 pounds, will she replace all 5 pounds of muscles? Our animal studies suggest that she won't, so Christine may replace 18 pounds of fat and just 2 pounds of muscle. She may be the same weight before and after this cycle, but her metabolic rate would be lower after the cycle because she has more fat, which is less metabolically active than muscle.
Cycling may also influence food preferences. Rodin and her student, Danielle Reed, tested the effect of cycling on female rats' preference for carbohydrate, protein and fat and found that cycling rats strongly preferred more fat in their diet. If this occurs in people it may have negative consequences for their health because high-fat diets have been linked with cardiovascular disease and certain cancers.
Weight cycling's effect on health is extremely important because weight loss is thought to improve health and weight gain to damage it. We are testing the effects of weight fluctuation on the immune system, risk of cardiovascular disease and susceptibility to breast cancer in animals. We are also working with scientists conducting the Framingham Heart Study, the largest and longest-running study of human coronary heart disease in the world. We are interested in the relationship of body weight to heart disease and are extending this inquiry to weight cycling.
Should people diet? For people who are 20% or more overweight--especially those with conditions such as hypertension, high cholesterol and diabetes--weight loss will probably lower their risk for serious medical problems.
But our research on yo-yo dieting indicates that going on and off diets repeatedly will make weight control difficult in the long run. Cathy, our heartbroken dieter, tried as hard as she could to lose weight but eventually drifted out of our program, still a heavy person.
Realistic Judgment Needed
So it is important for people considering a diet to think about the likelihood of making permanent habit changes. If there is doubt, the individual should consider waiting for a better time to begin. This shouldn't be a convenient excuse never to diet, but one should make a realistic judgment of whether the time is right.
A sensible approach to dieting includes a plan that you can weave into your life style. Good dieting emphasizes changes in what you eat, how and when you eat and physical activity.
Low-calorie diets (fewer than 800 calories per day) should not be undertaken without medical supervision. Quick-fix diets with magic foods, devices or pills will probably lead to rapid weight losses, but they will be followed by even faster regain. The body just wasn't designed to be yo-yo.