Diet, Exercise, and Health

Abstract & Commentary

Synopsis: This study confirms the beneficial effect of weight reduction on hyperinsulinemia in obese individuals but that participation in supervised exercise did not result in additional improvement in weight loss or insulin sensitivity.

Source: Weinstock RS, et al. Arch Intern Med 1998; 158:2477-2483.

The objective of this study was to determine the effects of a 48-week, supervised diet and exercise program on weight and insulin sensitivity after initial weight loss and weight maintenance and then subsequent weight gain over 96 weeks.

Forty-five obese women, whose average body mass index (BMI) was 35.9 and whose mean age was 43.3 years, were randomly assigned to one of three treatment groups: diet alone; diet and aerobic training; and diet and strength training. All subjects received the same 48-week group behavior modification program and diet (~ 925 kcal/d for the first 16 weeks; ~ 1500 kcal/d thereafter). Exercising subjects were provided three supervised exercise sessions per week for the first 28 weeks and two sessions weekly until week 48. During weeks 48-96, the subjects were unsupervised.

The subjects achieved a weight loss of 13.8 kg by week 16, which was associated with decreased insulin levels (61.8% of baseline). There were no significant differences among groups in changes in BMI, weight, glucose tolerance, or insulin levels at weeks 16, 24, and 44. No additional beneficial effect of aerobic or strength exercise on insulin resistance, as reflected by serum insulin levels before and after a glucose load, was demonstrated. Twenty-two subjects, who were studied at week 96, maintained a loss of approximately 10% of initial weight. Insulin levels, however, had returned to pretreatment levels.

Weinstock and associates conclude that the study confirms the beneficial effect of weight reduction on hyperinsulinemia in obese individuals but that participation in supervised exercise did not result in additional improvement in weight loss or insulin sensitivity.

Comment by Ralph R. Hall, MD, FACP, FACSM

Taken at face value, this article could be hazardous to your patients’ health. It implies that exercise is not helpful with weight loss or with insulin resistance. Weinstock et al quote several of the papers in which Wing addressed the subject of exercise and diet but failed to mention her classic study demonstrating that moderate exercise had to be carried out at least four days per week to add to the weight loss of a low-calorie diet.

As a superviser of a "Diabetes Education and Exercise" program for more than two years, I found obese persons can exercise more than three days per week if their intensity and duration can be gradually increased. Weight training has practical aspects in that it increases strength, but it will also improve cardiovascular risk factors by improving lean body mass, insulin sensitivity, and the levels and quality of the lipoproteins.1

Two randomized clinical trials reported in the Journal of the American Medical Association compared the effects of exercise in a structured environment vs. exercise as part of routine lifestyle activities. Both studies, which were carried out with more precise measurements than those of Weinstock et al, demonstrated that increasing physical activity in previously sedentary individuals can improve cardiorespiratory fitness, lean body mass, blood pressure, and lipid profiles.2,3 The BMI average among participants was less in these two studies, although the groups studied by Anderson and associates had an average BMI of 31.5 and 32.4, respectively.

In an editorial that accompanies the two articles, Pratt states, "It is now clear that regular physical activity reduces the risk for coronary heart disease, diabetes, colon cancer, etc."4 He also notes that the two studies show that exercise can be effective when carried out as a part of lifestyle activities and, with careful instruction, can be as effective as supervised, structured programs. It should also be emphasized that the benefits of exercise are dose-related, but, as Pratt points out, "physical activity needs to become not just the right choice but an easy, sustainable, and enjoyable choice."

If one reads only the article by Weinstock et al, one might assume that exercise, no matter how often or how intense, would not help your patient to lose weight.

References

    1. Wallace MB. Med Sci Sports Exerc 1997;29:1170-1177.

    2. Dunn AL, et al. JAMA 1999;281:327-334.

    3. Anderson RE, et al. JAMA 1999;281:335-340.

    4. Pratt M. JAMA 1999;281:375-376.