A 1992 book titled Men Are From Mars, Women Are From Venus (4) was the most visible totem of a flurry of scientific and pseudoscientific interest in the biological/psychological differences between men and women. The field of exercise science was swept up in the controversy, with a spate of reports focused on gender or sex differences across a range of physiological systems. In addition to scientific interest, there are real-world applications to sex-based biology. In particular, the utility of exercise as a weight loss strategy has been fraught with controversy centered on sex-specific outcomes. There is a prevailing view that adding habitual exercise to a previously sedentary lifestyle is a more effective weight loss method in men than it is in women, a viewpoint amplified by John Cloud’s “Why Exercise Won’t Make You Thin” 2009 cover story in Time magazine (including cover photo of an exercising woman chasing a cupcake) (2). This viewpoint has permeated the lay public and reached its tentacles into textbooks and the “generally accepted as true” consciousness of the kinesiology and nutrition communities. There is even an appealing, albeit teleological, explanatory mechanism rooted in evolutionary biology; women, who bear a higher energy cost of reproduction, more effectively “defend” body weight by compensating for increased activity with less spontaneous movement, increased energy intake, or both.
In the accompanying article titled “Exercise and Weight Loss: No Sex Differences in Body Weight Response to Exercise” (1), Caudwell and colleagues in the Institute of Psychological Sciences at the University of Leeds review the recent literature with a critical eye to the role of exercise “dose” in modulating the weight loss response. Based on a careful review of their own work and that of others, the authors hypothesize that the disparity in weight loss attributed to sex actually is a result of differences in exercise energy expenditure. In many prior studies, exercise dose was not strictly controlled, resulting in uncertainty regarding the actual energy expenditure. Even when exercise was supervised, exercise dose was based on a certain intensity and duration of exercise rather than tightly regulating expenditure. As a result, the absolute exercise dose invariably is lower in women, who tend to be smaller and expend less energy, than in men. Caudwell and colleagues did a series of elegant studies in which they carefully titrated the dose of exercise energy expenditure across men and women so that it was applied more equitably. In their work, they see little evidence for a systematic sex difference in weight loss when energy expenditure was monitored carefully. In support of their conclusions, data from the recent Midwest Exercise Trial 2 by Donnelly and colleagues (3), in which they adjusted the exercise dose applied to men and women from their prior study, also show no sex-specific differences in weight loss. Therefore, the review by Caudwell concludes with a new theoretical model in which equivalent exercise energy expenditure is manifested in equal weight change, irrespective of sex.
At a time when “cutting-edge science” is often equated with asking previously unaddressed questions, the article by Caudwell et al. demonstrates the power of asking the same question in a better way. By using stringent experimental control and minimizing key confounding variables, their work makes an important contribution to the literature and addresses the practical question of how important is exercise in weight loss? In addition, they demonstrate that, at least in this case, women and men arise from the same planet.
Department of Kinesiology
University of Massachusetts
1. Caudwell P, Gibbons C, Finlayson G, Näslund E, Blundell J. Exercise and weight loss: No sex differences in body weight response to exercise. Exerc. Sport Sci. Rev
. 2014; 42 (3): 92–101.
2. Cloud J. Why exercise won’t make you thin. Time Magazine
. Aug. 9, 2009
3. Donnelly JE, Honas JJ, Smith BK, et al. Aerobic exercise alone results in clinically significant weight loss for men and women: midwest exercise trial 2. Obesity
. 2013; 21: E219–28.
4. Gray J. Men Are From Mars, Women Are From Venus: The Classic Guide to Understanding the Opposite Sex
. New York (NY): HarperCollins Publishers; 1992.