Letters The science of obesity

Author’s reply to Cottrell

BMJ 2013; 346 doi: http://dx.doi.org/10.1136/bmj.f3125 (Published 22 May 2013) Cite this as: BMJ 2013;346:f3125
  1. Gary Taubes, co-founder1
  1. 1Nutrition Science Initiative, San Diego, California, USA
  1. gataubes{at}gmail.com

Cottrell cites a World Sugar Research Organisation report claiming that world consumption of caloric sweeteners (such as sucrose and high fructose corn syrup) has been static for decades.1 These data are difficult to reconcile with International Sugar Organisation reports that world sugar consumption rose between 2001 and 2011—by an average of 2.2% yearly, nearly twice the population growth rate.2

Such trends can neither confirm nor refute the hormonal-regulatory defect hypothesis or sugar’s role in obesity. Cottrell assumes incorrectly that caloric sweetener consumption must increase to explain the obesity epidemic. If a threshold effect is at work, then prevalence can increase if sugar consumption is above that threshold. This is another argument for well controlled experiments to establish causality.

Cottrell claims that insulin concentrations remain low in healthy people, but the study he cites reports a long term deterioration of insulin sensitivity in this population.3 The accompanying editorial suggests that it is “the effect of progressive inactivity and middle age spread.” It could also be the effect of a dietary trigger of “progressive inactivity and middle age spread.”4 Such observations can’t differentiate.

Cottrell suggests that the hormonal-regulatory defect hypothesis is incorrect because de novo lipogenesis is low during carbohydrate overfeeding, a common misconception. As the reference Cottrell cites says, body fat stores can be increased “not by conversion of the carbohydrate to fat. Instead, the oxidation of dietary fat [is] suppressed and fat storage thereby increased.”5

Despite our disagreements, it’s crucial to remember that this discussion is about real people—their health and quality of life. The past 50 years has shown us that we need new information and better science because the conventional wisdom isn’t working. Our friends, families, and neighbours have a spectrum of metabolic disorders; it is incumbent on us to challenge conventional thinking when it is clearly failing.


Cite this as: BMJ 2013;346:f3125