Diet and Myths Weight-Loss Lore and Controversies - Why Diets Fail

term obesity people maintenance

Most diets do not fail—they work to produce weight loss. Historically diets have been considered to have "failed" when lost weight is regained. Many nutritionists and obesity researchers believe that diets fail because most are not sustainable. The more restrictive the diet, the less likely an individual will be to remain faithful to it because in general, people cannot endure extended periods of hunger and deprivation. Another reason diets may fail is that they neglect to teach dieters new eating habits to assist them to maintain their weight loss. Most overweight people gained their excess weight by consuming more calories per day than they needed. Dieting creates a temporary deficit of calories or specific macronutrients such as carbohydrates or fat. Since the weight-loss diet is viewed as a temporary measure with a beginning and an end, at its conclusion, most dieters return to their previous eating habits and often regain the lost weight or even more weight. Many nutritionists and dieticians who work with people who are overweight or obese assert that diets do not fail, instead dieters fail to learn how to eat properly to prevent weight regain.

Consumers are not the only ones who believe diets are doomed to failure; many health professionals and researchers cite the statistic that 95% of diets fail. The American Obesity Association (AOA) attributes this oft-cited statistic to Albert Stunkard of the University of Pennsylvania and a director emeritus of the AOA. Stun-kard put forth the 95% failure rate in an account of research he performed in 1959, which involved advising 100 overweight patients to diet, with no follow-up or support to increase their adherence to the diet. In an editorial published on the AOA Web site, "Why Don't They Get It?" (, March 1, 2002), Morgan Downey, AOA executive director, observed that this statistic has been applied to every existing weight-loss program from surgery and antiobesity drugs to group support and behavior-modification programs. Downey wondered why such an old statistic, derived from such a small sample of subjects who had been offered nearly no counseling other than a printed diet, would still be cited almost a half century after its publication. He speculated that "It may be that it actually reflects people's own experience. Or it may be used to discourage vigorous weight loss efforts. Maybe some of us with obesity find it helpful to have company in our own weight loss failures."

Improving Long-Term Weight Loss

More recent research has demonstrated that dieters find it challenging to maintain weight loss; however, it has refuted the 95% failure rate. In "Successful Weight Loss Maintenance" (Annual Review of Nutrition, vol. 21, no. 1, July 2001), Rena Wing and James Hill proposed defining "successful long-term weight loss maintenance as intentionally losing at least 10% of initial body weight and keeping it off for at least one year." Using this definition the investigators offered more favorable outcomes of weight-loss efforts. Wing and Hill reported that more than 20% of overweight or obese people can and do lose 10% or more of body weight and maintain the weight loss for more than a year. Analyzing data from the National Weight Control Registry, they also found that people who successfully maintained long-term weight loss—an average weight loss of 30 kg (66.14 lbs) for an average of 5.5 years—shared common behaviors that promoted weight loss and weight maintenance. These behavioral strategies included eating a diet low in fat, frequent self-monitoring of body weight and food intake, and high levels of regular physical activity. The investigators also posited that weight-loss maintenance may become easier over time because they observed that once weight loss had been maintained for two to five years, the chances of longer-term success were greatly increased.

Although Wing and Hill offered more optimistic estimates of successful weight loss and weight maintenance than Stunkard had reported, there is obviously considerable room for improvement. Research supported by the National Institute of Diabetes and Digestive and Kidney Diseases and National Heart, Lung, and Blood Institute and led by Robert Jeffery, Division of Epidemiology, School of Public Health, University of Minnesota, attempted to identify areas of investigation that might produce strategies to assist more people to control their weight effectively ("Long-Term Maintenance of Weight Loss: Current Status," Health Psychology, vol. 19, no. 1, supplement, January 2000). Jeffery and his colleagues asserted that despite high rates of dieting and the possibility of long-term success in voluntary weight loss overall, successful weight losses are being offset by failures. The investigators speculated that the reason for this overall lack of success is that improvements in long-term weight loss have thus far lagged behind improvements in short-term weight loss.

Jeffery and his colleagues, one of whom was Albert Stunkard, described the typical course of weight loss and regain among people participating in behavioral treatment for obesity as rapid initial weight loss that slows, with maximum weight loss achieved approximately six months after treatment began. Thereafter weight regain begins and continues until weight stabilizes at, or slightly below the starting weight. The investigators speculated that the behavior changes prescribed are sufficient for weight loss, and failure to maintain behavior changes may be due to loss of knowledge and skills, loss of motivation, or unpleasant side effects of behavior change such as hunger, psychological stress, or social pressure. Historically, researchers favored either a biological interpretation of the challenge of weight maintenance—the importance of biological determinants of body weight—or a behavioral explanation. Behavioral scientists interpreted the weight loss—weight regain pattern as evidence of how difficult it is to achieve lasting change in environmental factors that influence behaviors.

The investigators classified efforts to improve long-term maintenance of weight loss as attempts to increase the intensity of initial treatment, extend the length of treatment, alter dietary and exercise prescriptions, enhance motivation, and teach maintenance-specific behavioral skills. An example of high-intensity obesity treatment is use of very-low-calorie diets (VLCDs). VLCDs restrict food intake for periods of two to three months to 600-800 calories per day, substantially lower than conventional low-calorie diets, which range from 1,000-1,200 calories per day. VLCDs consistently produce larger initial weight losses than conventional low-calorie diets. However, they have not proven successful in improving long-term weight loss. The larger, rapid weight losses generated by severe calorie restriction are followed by larger and more rapid regains, which offset the initial losses. Two or more years after treatment, people who were placed on VLCDs fared no better than those who lost weight using less intense regimens.

Treating obesity like such chronic diseases as diabetes and high blood pressure that require ongoing management appears to be helpful; however, attendance at treatment sessions declines over time and is associated with weight regain. Efforts to modify dietary and exercise prescriptions have focused on emphasizing exercise instead of focusing solely on dietary changes. Although some studies showed that the addition of exercise improved short-term weight loss and weight loss at eighteen-month follow-up visits, exercise was found to slow but not prevent weight regain.

Approaches to enhance motivation have focused on two areas—tangible financial incentives and improved social supports. Several studies found that modest payment as a reward for weight loss did not enhance initial weight loss nor did it slow the rate of regain after initial weight loss. Strategies to improve social supports have emphasized including spouses or significant others in the weight-loss process to teach them to provide social support for their partners' weight-loss efforts. Such strategies have demonstrated modest success as have contracts in which groups agreed to aim for individual or group weight-losses.

Teaching patients skills that are useful for weight maintenance as opposed to weight loss emphasizes that there are two distinctly different sets of strategies—one set focuses on weight loss and the other on maintaining a stable energy balance around a lower weight. The most commonly used model for teaching maintenance-specific skills is relapse prevention, which involves teaching people to identify situations in which lapses in behavioral adherence are likely to occur, to plan strategies in advance to prevent lapses, and to get back on track should they occur. Relapse prevention is based on the idea that breaking the "rules" in terms of remaining faithful to diet and exercise programs may often lead to negative psychological reactions that in turn prompt reversion to pre-weight-loss behaviors. To date, only one study has examined the effectiveness of this approach. Researchers hypothesized that learning and practicing a well-defined, positive response to relapses might help people sustain weight losses. However, their findings did not support this hypothesis.

Jeffery and his colleagues acknowledged that weight management is a continuing source of fascination and frustration for researchers as well as dieters. They recommended that research consider additional areas including:

  • Considering obesity as a chronic disorder requiring continuous care, with the aim of developing cost-effective methods for delivering care indefinitely
  • Examining psychological, behavioral, biological, and environmental factors that relate to weight loss, maintenance of weight loss, and weight regain in order to identify the key factors associated with successful long-term weight loss
  • Improving the assessment of energy intake and expenditure and of behavior patterns associated with change in energy intake and expenditure
  • Examining the role of such behavioral preferences as inclination for energy-dense foods and physical activities in obesity and its treatment in an effort to answer such questions as "Can behavioral preferences or reinforcement values be changed in ways that would facilitate long-term weight loss? Do they change spontaneously after behavior changes?"
  • Researching why long-term outcomes of behavior treatment for obesity in children and adolescents have been more successful than treatment for obesity in adults
  • Learning more about the role of physical activity and social support in relationship to long-term weight loss
  • Discovering safer and more effective medications to treat obesity and developing new ways to integrate medications into effective programs of weight control

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