Treatment of Obesity by Moderate and Severe Caloric Restriction: Results of Clinical Research Trials

In 1958, Stunkard [1] summarized in two sentences the results of the previous 30 years' efforts to control obesity by dietary means: Most obese persons will not stay in treatment for obesity. Of those who stay in treatment, most will not lose weight, and of those who do lose weight, most will regain it. These conclusions were derived from a review of the literature and from Stunkard and McLaren-Hume's [2] observation of 100 consecutive patients treated by conventional diets providing 800 to 1500 kcal/d. Only 12 patients lost 9.1 kg (20 lb) or more, and only 1 patient lost 18.2 kg (40 lb). Thirty-nine patients failed to return to the nutrition clinic for a second visit. Long-term weight losses were equally discouraging. This article reviews recent studies of the short- and long-term effectiveness of both moderate and severe caloric restriction, as determined by randomized clinical trials. The effectiveness of moderate caloric restriction was assessed by examining all studies published in four behavioral journals in 1974 and 1978 and from 1984 to 1990. All controlled studies of severe caloric restriction that included follow-up data were reviewed. Where possible, current findings are compared with Stunkard's [1], which are often thought to characterize current treatment. Moderate Caloric Restriction Research trials usually prescribe a diet of 1200 kcal/d of conventional foods for obese women and a diet of approximately 1500 kcal/d for obese men. Patients are encouraged to consume approximately 15% of calories from protein, no more than 30% from fat, and the rest from carbohydrate. Some trials allow participants to select their own foods, whereas other trials provide greater structure in the form of meal plans, such as that developed jointly by the American Diabetes and American Dietetic Associations [3]. The common practice of prescribing the same diet for all patients creates energy deficits and markedly different weight losses [4]. Thus, a short, mildly obese woman with an energy expenditure of 1500 kcal/d will lose only 0.5 kg (1 lb) a week on a 1000-kcal/d diet. By contrast, a taller, heavier woman with a daily energy expenditure of 2500 kcal/d will lose approximately 1.4 kg (3 lbs) a week on the same diet. This finding underscores the need to estimate, if not measure, the energy expenditure of overweight patients to select an appropriate reducing diet [5]. Behavior Modification Most obese persons will lose weight when placed on an appropriately restricted diet [6]. The magnitude of their weight loss, after accounting for basal energy expenditure, depends largely on the adequacy of their adherence to the prescribed caloric intake and on the duration of the diet. Adherence appears to be partly a function of the intensity of the supervision provided by the weight loss program. Thus, persons who are given diet plans or treatment manuals by their health providers and told to come back in 3 months receive minimal supervision and are unlikely to lose significant amounts of weight. Similarly, the average weight loss of persons who participate in large-scale, community interventions [7] or self-help programs [8] is modest. The results of such efforts are likely to resemble those described by Stunkard in the 1950s. The introduction of behavior modification in the 1960s significantly improved the short-term treatment of obesity [9, 10]. Thus, all current research studies of the dietary management of obesity include elements of behavioral treatment, which provides patients with a set of principles for evaluating and modifying their eating and exercise habits as well as their emotional reactions to their weight. Patients keep daily records of their physical activity, food intake, and any difficulties encountered, which may then be reviewed with a dietitian, behavioral psychologist, or other provider. Brownell [11] has provided an excellent account of this approach in a 200-page manual. The structure of treatment is perhaps as important as the principles and techniques themselves [12]. Specifically, most behavioral weight-loss programs provide weekly instruction to groups limited to 10 to 20 participants. In addition, the length of treatment is specified in advance and usually lasts from 10 to 25 weeks. Thus, patients receive regular and intensive supervision. When this structure is adopted, more traditional dietary interventions may produce weight losses similar to those associated with the strongest behavioral programs [13]. Short-Term Weight Losses Table 1 provides a summary of randomized trials in which moderate caloric restriction was combined with behavior modification [14]. The studies were published in 1974 and 1978 and from 1984 to 1990 in the following journals: Addictive Behaviors, Behavior Therapy, Behaviour Research and Therapy, and Journal of Consulting and Clinical Psychology. Results of these studies are similar to those published in medical and nutrition journals. Table 1. Summary Analysis of Selected Studies from 1974 to 1990 Providing Treatment by Moderate Caloric Restriction and Behavior Modification* The table shows that current treatment (that is, studies from 1988 to 1990) produces an average weight loss of 8.5 kg in 21.3 weeks and is associated with attrition of approximately 20%. This weight loss is more than double that achieved in earlier studies. In 1974, for example, patients lost only 3.8 kg in treatment that averaged 8.4 weeks. The increase in mean weight loss from 1974 to 1990 could be attributable to several factors, including the heavier initial weights of patients in the most recent studies; heavier patients typically lose the most weight. The best explanation, however, for the larger losses is probably the longer duration of treatment. The average weekly rate of weight loss of 0.4 to 0.5 kg has not changed since 1974; however, longer treatment periods have given patients more time to lose weight. This finding has led investigators to extend treatment up to 1 year in hopes of producing average losses as great as 20 to 25 kg. In a 40-week study, Perri and associates [15] found that patients lost 9.9 kg in the first 20 weeks of therapy but only an additional 3.6 kg in the second 20 weeks. In a similar, 52-week study [14], patients lost 11.9 kg during the first 26 weeks but only an additional 2.5 kg at the end of the year. In both studies, patients remained substantially overweight at the end of treatment. Thus, the size of the weight losses that can be produced by conventional reducing diets (as combined with behavior modification) appears to be limited. It is unclear whether these limits result primarily from metabolic influences or from reduced motivation and adherence [16]. Long-Term Weight Losses The studies from 1984 to 1990 (see Table 1) show that patients treated by moderate caloric restriction regained an average of one third of lost weight in the year after treatment. This regain contrasts with the generally good maintenance of weight loss seen in the studies from 1974 and 1978. Patients in the early studies, however, lost smaller amounts of weight and were followed for briefer periods, thus allowing less time to observe possible weight regain. Longer-term studies indicate that patients regain increasing amounts of weight with increasing time from therapy [17, 18]. Most persons in research trials treated by moderate caloric restriction are likely to return to their baseline weight within 5 years of completing therapy. Improving Long-Term Results Perri and colleagues [13, 19] have shown that weight regain can be prevented by continuing care. They view obesity as a chronic disorder requiring long-term treatment, similar to the management of hypertension or diabetes. In a promising randomized trial [19], patients who lost 13.2 kg during an initial 20 weeks of treatment using moderate caloric restriction subsequently received 52 weeks of biweekly maintenance therapy in which they continued to attend group meetings and discuss weight control skills. At the end of this time, they maintained an average weight loss of 12.9 kg. By contrast, patients who received the initial 20-week weight-reduction program, but no maintenance therapy, regained almost 50% of their weight loss during the year. Additional studies have shown that regular patient-therapist contact facilitates maintenance of weight loss, whether the contact is in person, by telephone, or by mail [11]. Adding an exercise regimen to moderate caloric restriction also improves long-term results [20]. Both correlational studies [21] and randomized trials [22] have shown that persons treated by diet plus exercise are more likely to maintain their weight losses than are those treated by diet alone. In addition to increasing energy expenditure, exercise minimizes the loss of fat-free mass that typically accompanies weight reduction [23]. Regular exercise may also have favorable effects on mood, which facilitates adherence [24]. None of the studies summarized in Table 1 included programs of intensive exercise or weight maintenance therapy (as developed by Perri). Thus, the findings summarized in the table represent the short-and long-term results that can be expected with a typical course of treatment lasting 15 to 25 weeks. Better results can be achieved with more intensive interventions. Severe Caloric Restriction The failure in the 1950s of moderate caloric restriction to produce adequate weight losses in the significantly obese led investigators to explore the use of very-low-calorie diets (VLCDs) providing 800 or fewer kcal/d [14]. These diets provide large amounts of dietary protein (>50 g/d) of high biological quality and have been shown to spare fat-free mass while producing average weekly weight losses of 1.5 to 2.0 kg in women and 2.0 to 2.5 kg in men [25]. Protein may be obtained from lean meat, fish, and fowl, or from egg and milk sources. In the latter, the protein is powdered and later mixed with water (by the patient) to