Weight management and exercise: any advantage?

See corresponding article on page 576.

The prevalence of obesity has more than doubled over the past 40 y and affects both children and adults (1). At present, >37% of the US population is classified as obese, with the attendant increases in health care costs (2). The curvilinear relation between BMI and risk of mortality, diabetes, heart disease, stroke, and gall bladder disease shows that a 5-unit increase in BMI raises the mortality from diabetes by 116%, increases mortality from renal disease by 60%, and increases mortality from vascular disease by only 30% (3). Weight loss reduces risk factors for these diseases, and in some studies it reduces mortality (4), myocardial infarction (4), stroke (4), and diabetes (5). Improvements in risk factors can be produced by diet, exercise, or behavioral changes but with somewhat different patterns (6–9).

In the Framingham study, weight loss of 6.8% over 4 y was associated with a 21–29% decrease in the risk of hypertension (10). In a meta-analysis of 25 studies in 4874 individuals, Neter et al. (11) found that weight loss averaging 5.1 kg after diet and/or exercise programs reduced systolic and diastolic blood pressure by 4.44 and 3.47 mm Hg, respectively. Blood lipids and sleep disturbances also improved with weight loss (7). In a systematic review of long-term weight-loss studies and their applicability to clinical practice, Douketis et al. (12) found that dietary and lifestyle therapy provided <5 kg weight loss after 2–4 y and that this was not consistently associated with improvements in cardiovascular disease (CVD) risk factors except in individuals with concomitant CVD risk factors.

Because both diet and exercise can improve CVD risk factors, Weiss et al. (13), in this issue of the Journal, asked whether the effects of exercise were “additive” to the benefits of diet-induced weight loss. The study included 52 men and women who were overweight and who completed the study. Individuals were randomly assigned to 1 of 3 treatments, with a weight-loss goal of 7% over 12–14 wk. One group consumed a calorie-restricted diet, a second group adhered to an exercise regimen designed to produce the 7% weight loss without changing food intake, and the third group followed a combination of calorie restriction and exercise with half of the desired weight loss from each modality. Fat mass decreased by an average of 15% in the 3 groups; fat-free mass decreased by 2.6% in the calorie-restricted group and by 1.6% in the combined diet and exercise group (P < 0.002), with no change in the exercise-only group. This suggests, as have many other studies, that exercise can minimize the loss of lean body mass during weight loss, but in this trial the comparison was not quite significant (P = 0.06). By design, energy intake was different between the groups (P = 0.002); it decreased by −32% in the calorie-restricted group and by –27% in the combined diet and exercise group, but with no significant change in the exercise-only group (−7%; P = 0.11) (13).

In the exercise-only group, 22% of total energy expenditure came from exercise (412 kcal/d); in the combined diet and exercise group, 10% of total energy expenditure (217 kcal/d) came from exercise. Diastolic blood pressure decreased similarly in all groups. Systolic blood pressure was significantly reduced in the calorie-restricted and combined groups, but not in the group with exercise alone (P = 0.07 for comparison between systolic blood pressure groups). HRs decreased, but there was no difference between the groups (13).

Total cholesterol, LDL cholesterol, and non–HDL cholesterol decreased significantly and to a similar extent in all 3 groups. HDL-cholesterol concentrations did not change and were not different between groups. Triglycerides declined significantly in the pooled data, but there was no difference between groups. Glucose decreased by 3%, insulin by 25%, and the HOMA-IR by 70%, but there was no difference between groups. C-reactive protein did not change. Arterial stiffness, pulse wave velocity, and the augmentation index did not change with weight loss and were not different between groups (13).

Exercise and dietary weight losses did not appear to be additive in this study. It is possible that larger weight loss or a longer duration of weight maintenance might have produced different outcomes. The weight loss of 7% in this study (13) and in the Look AHEAD (Action for HEAlth in Diabetes) study (14) improved CVD risk factors but did not reduce the incidence of “hard” endpoints such as myocardial infarction, stroke, or death (14). In contrast, surgically induced weight loss in the SOS (Swedish Obese Subjects) study produced a significant reduction in mortality and in the incidence of myocardial infarction, stroke, and diabetes (4). Improvements in CVD risk factors associated with the DASH (Dietary Approaches to Stop Hypertension) dietary pattern (15) or the Mediterranean-style diet (16) may have been detected had these dietary patterns been implemented by Weiss et al. (13).

The current study focused on CVD risk factors. However, weight loss profoundly reduces the risk of developing diabetes (5) and reduces the mortality from diabetes (3), and it may make more sense to focus on this endpoint rather than on CVD risk when examining the impact of weight loss (3).

One important remaining question not addressed by this study is whether the hormonal and metabolic changes that occur with weight loss and that predict weight regain changed differentially with diet and exercise. With weight loss, total energy expenditure, triiodothyronine, thyroxine, leptin (17), insulin, cholecystokinin, polypeptide YY, and glucagon-like peptide 1 decline, whereas ghrelin increases (18). The addition of exercise might blunt some of these changes, just as it did the loss of fat-free mass in the study by Weiss et al. (13). If this is borne out, then exercise may have some benefit during weight loss; otherwise, it seems to add little.

According to the authors, “A straightforward interpretation of the findings from the present study is that weight loss itself provides the major cardioprotective effect of calorie restriction and exercise and that the benefits do not depend on which approach to weight loss is used” (13). I would agree, but would modify this to suggest that it was the “fat loss” that was the major contributor because it decreased similarly in the 3 groups, in contrast to fat-free mass and maximal oxygen consumption, which were directly related to the degree of imposed exercise.