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Weight cycling is losing weight by dieting, regaining that weight and possibly more within a few months to a year, dieting and losing weight again, then putting the weight back on. Weight cycling is also called yo-yo dieting. It is the opposite of weight maintenance.
At any given time, about one-third of Americans are trying to lose weight. Many of them succeed in the short term, but the number of people who can keep the weight off for more than a year is small (around 25%), and the number that make the lifestyle changes necessary to keep weight off for five or more years even smaller (less than 10%). The constant cultural pressure to be thin, both for social and health reasons, leads to a cycle of dieting and weight loss followed by weight gain, and then more dieting. The changes in weight can be as small as 5 lb (2.3 kg) or as great as 50 lb (23 kg).
Researchers generally place weight cyclers into one of three categories.
- Severe weight cyclers have lost 20 lb (9 kg) or more three or more times.
- Moderate weight cyclers have lost 10-20 lb (4.5-9 kg)three or more times.
- Mild weight cyclers have lost 5-10 lb (2.3-9 kg) three or more times.
More women than men are weight cyclers, just as more women than men go on diets. Weight cyclers can be of any race, ethnicity, or age. Researcher are finding that weight cycling is beginning at an earlier and earlier age, probably because of the increase in childhood obesity.
Most weight cyclers are overweight, defined as a body mass index (BMI) of 25.0-29.9, obese, defined as a BMI of 30-39.9, or morbidly obese, with a BMI of 40 or above. The majority of studies are done on people who are overweight or obese.
Adolescent girls of normal weight may also become weight cyclers because of cultural pressures to be thin and/or because they have a distorted body image. Actors, who may need to bulk up or slim down for a role, and athletes, who often gain weight in the off season and lose it during pre-season training are other examples of normal-weight people who may be weight cyclers. Much less research is done on normal-weight people who weight cycle than on overweight and obese people who weight cycle. Most research on normal-weight yo-yo dieters is done on adolescent girls. Many studies have found that binge-eating, where an individual uncontrollably eats abnormally large amounts of food at one sitting, is fairly common among weight cyclers.
Weight cycling is not a disease, but is a sign of repeated attempts and failures to maintain weight. Its cause is simple—a period of during which the individual takes in fewer calories than she uses that results in weight loss followed by a period when the individual eats more calories than she uses that results in a weight gain. However, understanding why weight cycling occurs and determining if these changing periods of calorie intake affect both future weight loss and health is complex.
In the 1980s, obesity researchers began asking whether these failed attempts at permanent weight loss affect the indivual's health or ability to lose weight in the future. Weight and weight cycling are difficult topics to research in humans because so many different physical and emotional factors affect the process of weight gain and loss. These include:
- genetics. Twin and family studies have shown that there is an inherited component to weight, just as there is to height. As scientists have become more adept at isolating individual genes, they have found close to 300 genes that may play a role in determining weight. Although inheritance is not necessarily destiny—plenty of thin people have obese parents and siblings—genetic influences do help explain why some people gain weight more easily than others and have more difficulty keeping off the weight they lose.
- hormones. Ghrelin is a hormone produced in the stomach that stimulates appetite. It increases before meals and decreases after meals. Leptin is a hormone produced by fat cells (adipose tissue) that has the opposite effect. It tells the brain that enough food has been consumed and that the individual should stop eating. Differences in the levels of these hormones or in the body's responsiveness to them appears to play a role in losing and regaining weight.
- psychological factors. Many people start a diet with unrealistic expectations about how much weight they will lose, how fast the weight will come off, how much effort it will take, and how many permanent lifestyle changes they will have to make to keep the weight off. These attitudes all influence whether the individual will weight cycle. In addition, people who weight cycle are more likely to have depression and to be binge eaters with impulse-control issues.
- social factors.Many social events revolve around eating. People who feel they need to eat to please others or who have impulse-control difficulties often eat more than they intend in social situations. The trend toward super sizing restaurant portions reinforces the tendency to eat too much in social settings.
- Activity level. Studies show that people who are dieting consistently underestimate how many calories they burn in exercise. In general, the more active a person is, the easier it is for her to maintain a weight loss.
- Lack of nutritional information. Studies show that people consistently underestimate how many calories they eat and overestimate the amount of food that makes up a healthy portion. Although people who are successful in keeping weight off for many years tend not to strictly count calories, they are very aware of what and how much they eat.
Research on weight cycling
Starting in the 1980s researchers began testing a theory called the “set point” theory of weight cycling. This theory suggested that each individual has a natural set point for weight to which the body always tries to return. To explain this, researchers have suggested that the body has feedback mechanisms that adjust the metabolic rate so that fat stores are maintained at a relatively constant level.
The set point theory of weight cycling was first tested on weight-cycling mice that were made obese and then put on a diet more than once. Researchers found that when mice were fed a normal diet after losing weight on a calorie-restricted diet, they gained back the weight they had lost and more, and that during a second round of dieting, it took them longer to lose the weight that they had gained. This seemed to support the set point theory. However, research needed to be done on humans to prove the theory.
Doing a well-controlled weight cycling study on humans is difficult. It is unethical to manipulate the weight of volunteers the way the weight of laboratory animals is manipulated because there are clear and undisputed health risks to being overweight. Instead, researchers must depend on volunteers who self-report weight-cycling in the past. In addition, studies must compensate for differences in age, gender, health history, activity, and other lifestyle factors that are not an issue with laboratory animals. Some of the most tightly controlled human studies were done as inpatient studies where obese individuals were put very low calorie diets (less than 450 calories per day) under medical supervision to stimulate rapid weight loss. This type of extreme dieting does not necessarily reflect the way the majority of people diet in the real world. Given the variety of factors that affect human studies of weight cycling, it is not surprising that results concerning the effect of weight cycling on health are conflicting.
Several small studies done in the mid 1990s found that metabolic rate, or the rate at which a person burns calories, decreased after weight loss, supporting the set point theory. Later, more rigorously controlled studies found that after a temporary initial decrease, metabolic rate returned to pre-weight loss values. Based on these more recent findings, the National Institutes of Health takes the position that it should not be harder to lose weight when dieting after weight cycling. However, as people age they burn calories more slowly. This natural slowing of metabolism may make it appear that it becomes harder and harder to lose weight after several cycles of yo-yo dieting.
Other studies have looked at whether people who gain back the same amount of weight as they have lost have a higher percentage of body fat than they did before they weight cycled. In other words, did they lose muscle, but gain back fat? Researchers have found that people gain back muscle and fat in the same proportion that they had before they dieted, but that in some people the fat is distributed differently in their body. In these people weight cycling tends to put more fat back on the stomach and less on the thighs and buttocks. This may have health implications, as people who have more fat in the stomach area are more likely to develop type 2 (adult-onset) diabetes.
Research on weight cycling and weight maintenance is going on at many institutions. Individuals interested in participating in a clinical trial at no cost can find a list of research projects currently enrolling volunteers at <http://www.clinicaltrials.gov> At the site, search under “weight maintenance.”
Nutritional and dietetic concerns related to weight cycling are the same as those related to dieting and obesity in general. A nutritionist or dietitian can help plan a healthy weight-loss program and a weight maintenance program that will reduce weight cycling.
Most people who lose weight gain it back. A significant number of people gain back more than they lost. This can be make the individual feel like a failure and give her an excuse to stop trying to lose weight. Even modest weight loss has health benefits. Although weight loss relapses are common, losing weight, even if it returns, is healthier than not losing it, so long as the individual follows a balanced weight-loss program.
Studies have found that people who successfully maintain their weight loss and do not weight cycle are those who are prepared to make changes in their lifestyle. One study found that whether dieters lost weight using a liquid diet, a formal weight-loss program such as Weight Watchers, or a self-constructed weight loss program, everyone who successfully kept weight off for five years or more incorporated exercise into their daily routine. They also permanently changed their eating habits to eat a lower calorie diet. Another study found that inability or unwillingness to make behavioral changes with regard to eating and exercise was the most common predictor for regaining weight lost during dieting.
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Tish Davidson, A.M.