Effects of dieting and exercise on resting metabolic rate and implications for weight management
Josephine Connolly, Theresa Romano and Marisa Patruno
Department of Family Medicine, University Hospital and Medical Center, SUNY Stony Brook, Stony Brook, New York 11794-8461, USA.
Received 13 August 1998; Accepted 19 November 1998.
This two-part study is based on the assumption that a decrease in calorie intake and weight loss is associated with a decrease in resting metabolic rate and fat oxidation. The purposes of the study are as follows: (i) to determine if exercise training facilitates the maintenance of weight loss by attenuating the reductions in resting metabolic rate, resting fat oxidation and/or fat oxidation in the 5-hour post-prandial period; and (ii) to prospectively compare the maintenance of weight loss and changes in body composition and resting metabolic rate among subjects participating in aerobic or resistance training. All testing was done while subjects resided at a university clinical research centre.
In the first study, 20 older subjects (aged 56–70 years) underwent an 11-week weight-loss program. Subjects were educated on self-selecting diets meeting the following criteria: 900–1100 kilocalories per day, 60% carbohydrate, 15% protein and 25% fat. Subjects kept food diaries which were reviewed by a registered dietitian at weekly meetings. During the twelfth week, subjects were requested to increase their intake to allow for weight maintenance and stabilization of weight for post-diet measurements.
Subjects lost a significant amount of weight, approximately 9% of baseline weight (95.2 ± 3.2 kg), a significant amount of fat-free mass, approximately 5% of baseline (52.6 ± 2.7 kg), and a significant amount of fat mass, approximately 15% of baseline (42.6 ± 1.8 kg). In addition to losing mass, the following significant changes from baseline measurements were reported in the post-diet assessment period: a 15% decrease in absolute resting metabolic rate (1789.8 ± 80.2 kcal/24 hours, baseline), and an 8% decrease in resting metabolic rate relative to fat-free mass (33.8 ± 0.7 kcal/24 hours/kg fat-free mass, baseline).
In the second study, 18 of the 20 weight-reduced subjects began a 12-week exercise regimen, consisting of either aerobic training or weight training. Subjects followed progressive training programmes to elicit 80% of one-repetition maximum strength for weight trainers, and a minimum of 50% of peak oxygen uptake for 60 minutes for aerobic trainers. All subjects attended supervised exercise sessions three times per week.
After the 12-week training period following the initial diet intervention, the weight-training group did not ex-perience further weight loss, but maintained the weight lost during the initial 11-week diet period. Nor did they experience any significant changes in fat-free mass or fat mass, although the trend for increased fat-free mass approached significance (P = 0.071). The aerobic trainers experienced a significant further decrease in weight (2.5 ± 0.6 kg) and a significant further decrease in fat mass (1.8 ± 0.8 kg), and their fat-free mass remained unchanged.
In addition, there were between-group differences in body composition such that the aerobic trainers lost weight and the resistance trainers' weight remained unchanged. Trends in fat-free mass were also significantly different in that the weight trainers experienced a trend toward increasing fat-free mass and the aerobic trainers experienced no change in fat-free mass. Although changes in absolute resting metabolic rate in the weight training group approached significance (P = 0.068), there were no significant changes in resting metabolic rate, absolute or per kilogram mass, within the two groups or between the two groups.
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