Study Question: In 2008, federal guidelines recommended at least 150 minutes per week (7.5 metabolic equivalent [MET] hours per week) of moderate-intensity activity for “substantial health benefits.” What is the association of physical activity with long-term weight changes among women consuming a usual diet?
Methods: This prospective cohort study involved 34,079 healthy women participating in the Women’s Health Study from 1992-2007. At baseline and years 3, 6, 8, 10, 12, and 13, women reported their physical activity and body weight. Women were classified as expending <7.5,>Results: At baseline, mean age was 54.2 years; about 50% of the women expended <7.5 p =" 0.003)" p =" 0.002)." trend =" 0.56)" trend =" 0.50)." color="#000099">Conclusions: Among women consuming a usual diet, physical activity was associated with less weight gain only among women whose BMI was lower than 25 kg/m2. Women successful in maintaining normal weight and gaining fewer than 2.3 kg over 13 years averaged approximately 60 minutes a day of moderate-intensity activity throughout the study.
Perspective: How many women 52 years of age would exercise 60 minutes a day in order to not gain more than 5 pounds over 13 years? One per 1,000? The authors had two posits, neither of which makes sense: 1) once overweight, it may be too late because physical activity is not associated with less weight gain; 2) sustaining high levels of physical activity (~60 minutes a day) is needed to successfully maintain normal BMI and prevent weight gain. While MET hours per week of activity is a reasonable way to estimate kcal/day of energy expenditure, over 95% of kcal of energy is expended at rest or during sleep. Weight gain in middle-aged men and women is highly related to increasing energy intake, which was not measured in these women. Adding the equivalent of one slice of bread per day (100 kcal) could on average result in ~10 pounds of weight gain in 1 year. The impact of supersizing and fast foods cannot be overcome by exercise.
Fuente: JAMA 2010;303:1173-1179