How Much Physical Activity to Avoid Weight Gain?

Abstract & Commentary

By Rahul Gupta, MD, MPH, FACP, Clinical Assistant Professor, West Virginia University School of Medicine, Charleston, WV. Dr. Gupta reports no financial relationship to this field of study.

Synopsis: Contrary to the current guidelines, in the long term, an average of approximately 60 min/day of moderate-intensity activity for women is required to be successful in maintaining a normal weight.

Source: Lee IM, et al. Physical activity and weight gain prevention. JAMA 2010;303:1173-1179.

Obesity has become a public health crisis in the united States. In the past three decades, obesity prevalence has steadily increased. Not only does the economic impact of this current epidemic loom over us, but the present generation of Americans may for the first time have a shorter life expectancy than their parents if we are unsuccessful in controlling this epidemic. Research suggests that the total health care costs attributable to obesity and overweight will more than double every decade. It is estimated that by the year 2030, health care costs attributable to obesity and overweight alone could range from $860 to $956 billion, which would account for 15.8%-17.6% of total health care costs, or $1 of every $6 spent on health care.1 Because we know that the majority of obese or overweight people who are successful in losing weight are not able to sustain that weight loss, it is a reasonable approach to avoid weight gain in the first place. Physical activity is clearly one method of preventing such weight gain. However, it is unclear at this time whether the 2008 federal guidelines recommending at least 150 min/week (7.5 metabolic equivalent [MET] hours/week) of moderate-intensity aerobic physical activity for individuals to obtain substantial health benefits is sufficient.2,3

In the current study, the authors conducted a prospective cohort study of 34,079 U.S. women (mean age, 54.2 years) consuming a usual diet from 1992 to 2007. Women were classified as expending < 7.5 , 7.5 to < 21, and ≥ 21 MET hours/week of activity at each time and change in body weight was measured at periodic intervals (21 MET is the equivalent of 420 min/week of moderate activity or 60 min/day). The researchers found that women gained a mean of 2.6 kg throughout the study period of 13.1 years. Only among women with a BMI of < 25 kg/m2 was there an inverse dose-response relation between activity levels and weight gain. So, more physical activity in these women was associated with a lower weight gain. Compared with women expending ≥ 21 MET hours/week, those expending 7.5 to < 21 MET hours/week gained 0.11 kg, whereas those expending < 7.5 MET hours/week gained 0.12 kg. The difference in weight gain between these last two groups was not statistically significant. In other words, women who were successful in maintaining a normal weight and gaining < 2.3 kg over 13 years averaged approximately 60 min/day (420 min/week) of moderate-intensity activity throughout the study; those who gained significantly more weight averaged less physical activity, with no difference in weight gain between the two lesser active groups.

Commentary

A decline in daily physical activity, including that during leisure time is clearly a major factor contributing to the current obesity epidemic. We know that physical activity is beneficial to health with or without weight loss. We also know that most people gain some weight as they age. However, the question of how much daily physical activity is required to prevent weight gain remains. In addition to the above mentioned federal guidelines, the Institute of Medicine (IOM) suggests that 420 min/week (60 min/day) of moderate-intensity activity may be recommended for individuals to avoid becoming overweight or obese.4 The above study clearly supports the IOM recommendations and perhaps heralds that it may be time to revise the federal guidelines once again. However, it is also important to note the limitations of this study. Self reporting of results such as physical activity and body weight can be subject to individual bias. The current study was limited to middle-aged women and therefore may not apply to other groups.

However, it is important to remember that weight gain results from an imbalance between energy consumed and energy expended. Therefore, whereas any amount of physical activity is clearly better than none for the body, the prevention of weight gain or weight maintenance is dependent upon a number of factors including physical activity, healthy diet, and control of concurrent chronic illnesses. Nevertheless, this is a significant study and serves as a reminder that guidelines and recommendations must be revisited and updated periodically to suit the changing needs of our population.

References

1. Wang Y, et al. Will all Americans become overweight or obese? Estimating the progression and cost of the US obesity epidemic. Obesity 2008;16:2323-2330.

2. Haskell WL, et al. Physical activity and public health: Updated recommendation for adults from the American College of Sports Medicine and the American Heart Association. Circulation 2007;116:1081-1093.

3. Blair SN, et al. The evolution of physical activity recommendations: How much is enough? Am J Clin Nutr 2004;79:913S-920S.

4. Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients). Washington, DC: National Academies Press; 2002.