Letters The science of obesity

Restricting dietary carbohydrate versus increasing physical activity in tackling obesity

BMJ 2013; 346 doi: http://dx.doi.org/10.1136/bmj.f3018 (Published 22 May 2013) Cite this as: BMJ 2013;346:f3018
  1. John C Peters, professor of medicine and chief strategy officer1,
  2. James O Hill, professor of medicine and executive director1
  1. 1Anschutz Health and Wellness Center, Aurora, CO 80045, USA
  1. john.c.peters{at}ucdenver.edu

Taubes’s portrayal of “energy balance” is inaccurate.1 2 Because the energy balance is a dynamic model—with interactions between energy intake, energy expenditure, and energy storage—it is not useful to ask questions like “is it carbohydrates or calories?” The best diet for managing weight depends on the level and nature of energy expenditure and the size and composition of energy stores. Current science suggests that obesity results from a failure to burn fat, which can be rectified by reducing energy intake below expenditure (for example, by eradicating dietary carbohydrates) or providing a fat burning stimulus—physical activity.

Taubes’s main assumption is that we are doomed to be a sedentary population with poor cardiorespiratory fitness and must eliminate carbohydrate from our diets to be able to burn fat. It is equally logical to assume that we are doomed to consume high energy foods so we must become more active to turn on fat burning. Why must we make either assumption?

Taubes ignores the role of physical activity. If we worry about obesity because of its impact on health, it may be misguided to focus on one dietary ingredient given that the best predictor of all cause mortality is cardiorespiratory fitness, which is driven by physical activity.3 Scientists report that elite athletes have essentially no measurable metabolic disease despite eating a high carbohydrate diet. Similarly, the Amish, who are highly physically active as part of their culture have essentially no obesity, yet they do not subsist on a low carbohydrate diet.4

The crux of this discussion is how best to change population behaviour—restricting one dietary component or increasing physical activity. Let’s make sure that as we debate this everyone is transparent about the assumptions they are making.


Cite this as: BMJ 2-013;346:f3018


  • Competing interests: PCP and JOH are co-investigators on an American Beverage Association research grant. JOH is on General Mills company advisory board and McDonald’s company advisory board.

  • Full response at: www.bmj.com/content/346/bmj.f1050/rr/642656.