Are Athletes More Prone to Obesity?

One of the interesting but ‘paradoxical’ observations in my clinical practice is the rather large number of patients presenting with severe obesity, who have histories of successful competitive sports careers.

I have previously written about the notion that perhaps the same genes that can make you a successful athlete may well pose a risk factor for obesity.

Now, a study by Xue and colleagues from the University of Texas, published in PLoS One, suggests that genes that increase metabolic efficiency may indeed explain both the higher athletic prowess as well as the increased risk for obesity in Africans.

It is certainly no secret that Africans have held the most world records for track and field sports, including the men’s and women’s 100-meter dash, 200-meter dash, 400-meter dash, 800-meter dash, and even marathons.

Based on previous observations that Africans tend to expend less energy for the same level of physical activity as Europeans, the researchers reasoned that the genes responsible for this may also contribute to an increased predisposition to weight gain in this population.

The researchers used data from the HapMap project to examine African, Asian and European subjects for 231 common variants with possibly harmful impact on 182 genes involved in energy metabolism

This analysis found that Africans (3 out of 4 groups) had a significantly smaller genetic risk in the of possessing genes that would lead to inefficient energy metabolism than Europeans and Asians

As they point out:

‘In sport competitions, athletes need massive amounts of energy expenditure in a short period of time, so higher efficiency of energy generation might help make African-descendent athletes more powerful. On the other hand, higher efficiency of generating energy might also result in consuming smaller volumes of body mass. As a result, Africans might be more vulnerable to obesity compared to the other races when under the same or similar conditions.”

Obviously, as there is no such thing as the ‘African’ genome, in that all such genetic variants are also found in non-Africans, it may be reasonable to speculate that in general, genes that improve energy-efficiency (or rather absence of genetic variants that reduce it), thus increasing athletic prowess, can contribute to increased risk for obesity (when exercise ceases) in all populations.

While this notion is not dissimilar to the ‘thrifty genotype’ hypothesis, it does provide a novel ‘spin’ in that it suggest that the same ‘thrifty genotype’ that promotes obesity may also be responsible for making you a good athlete.

This certainly sounds very plausible considering how many obese patients I see, who have histories of being successful athletes. It also perhaps explains why so many of my patients can maintain rather high levels of physical activity once they find their way back into sports (for e.g. after bariatric surgery).

Edmonton, Alberta

Xue C, Fu YX, Zhao Y, Gong Y, & Liu X (2011). Smaller genetic risk in catabolic process explains lower energy expenditure, more athletic capability and higher prevalence of obesity in africans. PloS one, 6 (10) PMID: 22016803