Sunday, April 21, 2013

Endocrinological Hypothesis and Obesity: Cause or Mechanism?

I wanted to comment on a well-written essay recently published in the British Medical Journal by Gary Taubes, entitled:

The science of obesity: what do we really know about what makes us fat?

From the essay: The history of obesity research is a history of two competing hypotheses. Gary Taubes argues that the wrong hypothesis won out and that it is this hypothesis, along with substandard science, that has exacerbated the obesity crisis and the related chronic diseases. If we are to make any progress, he says, we have to look again at what really makes us fat

This essay, in my view, has two components - the first is the comment on the competing hypotheses for the cause of obesity, while the second concerns the 'sub-standard' research that has been undertaken throughout the past half-century in obesity research, regardless of the hypothesis.

1) I feel as though Taubes presents a straw-man of the energy balance hypothesis of weight gain. While it may be true that die-hard supporters will cite the 1st Law of Thermodynamics until they are blue in the face, I expect that most of the researchers, clinicians and academics who spend their lives trying to better understand obesity also understand that this Law its limits with respect to weight gain. Clearly, an individual who lives with a chronic, mild negative energy balance will not waste away until they disappear. There are metabolic compensation mechanisms to prevent this from happening (reduction in basal metabolism). Finally, the circular logic presented by Taubes that weight gain is caused by overeating, and that we can tell if an individual is overeating if they have weight gain, does not refute this hypothesis - it only supports it.

2) Taubes refers to the endocrinological hypothesis of obesity - although this hypothesis is never explicitly stated. It goes like this: due to intrinsic physiological abnormalities (say, altered insulin response) a positive energy balance is the result, rather than a cause of the condition of obesity. Sure, so weight gain is the result of aberrant physiological processes. This seems to substitute one mystery for another - what causes these aberrations in physiology? I think that Taubes is confusing this endocrinological hypothesis for a cause, when it is actually a mechanism of the cause. The cause of obesity is now believed to be an obesogenic environment, one that promotes abnormalities in a number of physiological processes associated with weight gain. But these processes are not the cause of weight gain, they are the mechanism through which weight gain results.

3) Taubes also compares smoking and lung cancer with eating and obesity. As previously mentioned on my blog (Obesity Prevention: applying lessons from anti-tobacco campaigns), eating is compulsory, often beneficial, and complex, while tobacco is optional, not beneficial, and simple. A poor comparison, and one that obesity researchers, clinicians and academics alike should discontinue using, especially in published literature.

4) Kudos to Taubes for pointing out that the majority of the research used to inform policy and public health messages is not exactly top-notch. He is correct to suggest that we absolutely need better quality research - that we need to go beyond associations to assess causation. However, there are many ethical considerations that cannot be avoided in this type of research. Also, I would personally agree with Taubes that the money we will save in health care expenditures and personal health (and productivity, quality of life, etc) will outweigh the amount of money that we put in to research obesity, should we conduct the required studies. Convincing the powers that be of this long-term financial benefit is another matter.

Overall, an interesting piece. I don't expect people to abandon the energy balance hypothesis just yet. We do need better quality research - more longitudinal studies and intervention studies - and I think the field is headed in the right direction here, albeit slowly. Do we have to "look again at what really makes us fat", as Taubes suggests? I don't believe so...but have a look and decide for yourself :)