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Children’s Hospital Division of Endocrinology Department of Medicine 300 Longwood Avenue Boston, MA 02115 E-mail: mark.pereira{at}channing.harvard.edu
Dear Sir:
We read with enthusiasm the recent article by Weinsier et al (1) that examined the association between energy expenditure and weight gain over 1 y in initially normal-weight sedentary women. Weinsier et al used state-of-the-art methods for measuring the entire spectrum of energy expenditure. The results showed that the women who gained a significant amount of body weight ( 6 kg; "gainers") expended 887 kJ/d (212 kcal/d) less, in light-to-moderate activities of daily living, than did women who maintained their normal body weight (weight gain 2 kg; "maintainers") over the same time period. They estimated that this difference in activity energy expenditure accounted for 77% of the excess positive energy balance in the gainers.
We concur with Wyatt and Hill’s (2) endorsement of the need for rejuvenating the public health promotion of physical activity. However, several additional methodologic issues and limitations of this study should be considered.
The study sample consisted of 2 very different groups of women—those who were at their normal body weight at baseline and those who had recently lost 10 kg in response to an energy-restricted diet. Not surprisingly, 19 of the 20 gainers were formerly overweight or obese, whereas only 6 of the 27 maintainers were formerly overweight or obese. A better study design would have been one in which the study subjects were derived from the same population, because there may be important behavioral or metabolic differences between persons with and without a recent history of significant weight loss.
On the basis of their data, Weinsier et al suggest that 80 min/d spent on activities of daily living of light-to-moderate intensity, 2- to 4-fold higher than current physical activity recommendations (3, 4), are necessary to prevent weight gain. However, they provided no information on the quantity or quality of physical activity during the follow-up period. Actual data concerning the quantity and quality of physical activity while the subjects were free-living during the 1 y of follow-up would be helpful in evaluating this assertion. How much more walking, stair climbing, and other activities of daily living were the maintainers doing relative to the gainers?
Finally, Weinsier et al suggest that physical activity is more important than is diet in the control of body weight, but they provided no data on the dietary habits of the subjects before weight loss and during the follow-up period. It is important to underscore that there were no significant changes over time in any component of energy expenditure in either group of women; the statistically significant findings remained limited to cross-sectional comparisons. Weinsier et al seem to draw the puzzling inference that the formerly overweight or obese women reduced their weight by dietary means, yet regained their weight solely as a result of low physical activity. Given that energy expenditure did not change in these inactive women, how can this inference be valid? The other half of the energy-balance equation, ie, energy intake and dietary quality during the follow-up period, certainly may have influenced weight regain.
At present, the best approach to preventing obesity and chronic disease appears to be through comprehensive lifestyle modification (5, 6), although the ideal dietary and physical activity prescriptions to control body weight over the long term remain elusive.
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