Weight loss: Are recommendations on physical activity duration optimal?

Combined with other healthy lifestyle habits, aerobic exercise (brisk walking, running, swimming, cycling, skating, stair climbing, etc.) is considered the most effective way for overweight or obese people to lose weight. International, national and provincial guidelines recommend that adults and seniors get at least 2.5 hours of moderate-to-high-intensity physical activity a week, or 150 minutes. “Physical activity sessions should last at least 10 minutes. At least two times a week, they should include activities aimed at strengthening muscles and bones, particularly those of the thighs and legs,” says the Quebec Ministry of Health on its website.But these recommendations, based on individual trials and old data, do not allow us to determine the dose-response association of exercise with weight, waist circumference and body fat in overweight and obese people. What duration and intensity of aerobic exercise are associated with greater weight loss and greater reductions in waist circumference and body fat in these individuals?To find out, a team of researchers from Semnan University of Medical Sciences, in Semnan, Iran, conducted a systematic review and dose-response meta-analysis of 116 randomized clinical trials involving 6,880 overweight or obese adults. Researchers considered changes in body weight, waist circumference, body fat, as well as adverse events, reduced medication use and health-related quality of life score.8+ weeksRandomized clinical trials were included with intervention durations of at least eights weeks evaluating the effects of supervised aerobic training on adults with overweight or obesity.Results showed each 30 minutes per week of aerobic exercise was associated with:a reduction in body weight of 0.52 kg (95% CI, -0.61 to -0.44 kg; n = 109 trials, GRADE = moderate)a 0.56 cm reduction in waist circumference (95% CI, -0.67 to -0.45 cm; n = 62 trials, GRADE = high)a reduction in body fat percentage of 0.37% (95% CI, -0.43% to -0.31%; n = 65 trials, GRADE = moderate)a reduction in adipose tissue in visceral (mean difference, -1.60 cm2 [95% CI, -2.12 to -1.07 cm2 ]; n = 26 trials, GRADE = high) and subcutaneous (mean difference, -1.37 cm2 [95% CI, -1.82 to -0.92 cm2 ]; n = 27 trials, GRADE = moderate) areas.Aerobic exercise was not associated with less use of anti-diabetic and anti-hypertensive medication but was associated with a modest increase in physical and mental aspects, as well as quality of life. The researchers also found an increase in mild and moderate adverse events, mainly musculoskeletal—knee and ankle injuries, knee or back pain and arthritis, as well as an increase in blood pressure. Finally, exercise was not associated with an increase in hypoglycemic reactions.The investigation, published in the Journal of the American Medical Association, thus reveals that 30 minutes of exercise per week modestly reduces weight, waist circumference and body fat in overweight or obese adults. “However, aerobic training of more than 150 minutes per week at moderate or higher intensity may be required to achieve clinically important reductions,” noted the authors. The researchers observed a 4.19 kg reduction in body weight associated with 300 minutes of aerobic exercise per week, and decreases in waist circumference associated with 300 minutes of aerobic exercise per week of 4.21 cm for moderate intensity and 5.34 cm for moderate to vigorous intensity.A linear reduction in body weight of 2.79 kg (95% CI, -3.29 to -2.29 kg) was associated with 150 minutes of exercise per week, and 4.19 kg for exercise duration at 300 minutes per week. “A similar linear reduction in body weight was also observed in dose-response analyses of trials with moderate, moderate-to-vigorous and vigorous exercise intensities,” they pointed out. For waist circumference, analysis of moderate-to-vigorous intensity trials showed a linear reduction associated with aerobic exercise dose. Thus, the degree of waist circumference reduction was -4.21 cm (95% CI, -6.85 to -1.58 cm) at 300 minutes per week of moderate-intensity aerobic exercise and -5.34 cm (95% CI, -9.05 to -1.63 cm) at 300 minutes per week of moderate-to-vigorous-intensity aerobic exercise.Duration, not intensity“The results suggest that the association of aerobic exercise with waist circumference exceeds the threshold set as the minimum clinically important difference for waist circumference (2 cm), with longer duration indicating greater waist circumference reduction,” the authors state. Finally, the greatest reduction in body fat percentage associated with exercise dose was observed at 150 minutes per week (mean difference, -2.08% [95% CI, -2.47% to -1.69%]), exceeding the threshold of 2% as the minimum clinically important difference. Maximum improvement in body fat percentage was associated with 150 minutes of exercise per week. Body fat mass was reduced by 2.03 kg [95% CI, -2.77 to -1.29 kg] at 100 minutes per week in the main analysis, and by an average of 2.23 kg [95% CI, -3.36 to -1.10 kg] in the analysis of trials with moderate to vigorous exercise intensity.Longer durations of aerobic exercise were therefore associated with greater reductions in body weight, waist circumference and adipose tissue. In contrast, exercise intensity was not associated with a credible difference between subgroups. “Specific point estimates for different durations and intensities of aerobic exercise may help patients and health professionals select the optimal duration and intensity of aerobic exercise according to their weight loss goals,” the authors concluded.The full study is available here.

Weight loss: Are recommendations on physical activity duration optimal?

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