SNPwatch: Jeans Too Tight? Don’t Just Blame Your Genes.

In 2009, 27% of Americans met the clinical criteria for obesity–a body mass index (BMI) of 30 or greater–7 percentage points higher than a mere 9 years earlier. Even this staggering 27% estimate may be too low. A large National Health and Nutrition Examination Study (NHANES) study estimated the prevalence of obesity at 34%. No wonder losing weight is a national preoccupation.But how much control do we really exert over our weight? We all know people who seemingly gorge themselves at every meal but never gain an ounce and others who all too easily pack on the pounds.In a paper published in PLoS Medicine, Shengxu Li and colleagues tackled a piece of that puzzle. Using a sample of 20,000 Europeans, they compared the predictive power of 12 SNPs known to influence BMI in sedentary and physically active individuals. While carrying a greater number of risky versions of these SNPs was associated with higher BMI in both groups, the association was much weaker in the physically active.In the sedentary group, each additional risky variant translated to a 0.21 increase in BMI, or an extra 1.3 lbs (592 g) for someone 5’7 (170 cm). By comparison, in the physically active people, each additional risky variant  translated to a 0.13 increase in BMI, or an extra 0.8 lbs (397 g) for someone 5’7 (170 cm). Leading a physically active lifestyle, they concluded, was associated with a 40% reduction in the genetic predisposition to obesity.Although we only have 9 of the 12 SNPs covered in our database, a quick analysis using our customers’ data replicated their findings. Carrying more risky variants was predictive of a higher BMI overall, but this effect was much more pronounced among our customers who reported low levels of physical activity.Of course, the 12 SNPs under investigation do not represent the totality of genetic predisposition to obesity. In fact, the 12 SNPs combined accounted for only 1.2% of the variation in weight among the sedentary individuals, and even less, 0.6%, among the physically active. Other genetic factors not measured in this research, such as rare variants associated with BMI, likely play a role as well.SNPwatch gives you the latest news about research linking various traits and conditions to individual genetic variations. These studies are exciting because they offer a glimpse into how genetics may affect our bodies and health; but in most cases, more work is needed before this research can provide information of value to individuals. For that reason it is important to remember that like all information we provide, the studies we describe in SNPwatch are for research and educational purposes only. SNPwatch is not intended to be a substitute for professional medical advice; you should always seek the advice of your physician or other appropriate healthcare professional with any questions you may have regarding diagnosis, cure, treatment or prevention of any disease or other medical condition.
  • Alan Bauerschmidt

    Some of the indicated SNPs listed in the Spitton article are not in the 23andMe database.

    • @Alan,

      Thanks for pointing that out. I think the SNP you are referring to is rs7498665. It turns out that rs7498665 is only genotyped on an older version of our platform, so some customers will see data for it but most will not. Luckily, there is another SNP genotyped in all customers that correlates perfectly with rs7498665 in European and Asian populations (and almost perfectly in African populations), so I’ve added that to the list above.

  • forest

    I just want to point out that BMI is utter nonsense. If you have more muscle than the average person, your BMI will reflect it as an indicator of being obese. Thus most bodybuilders are obese under the BMI standards. It can be assumed that half the population has higher than average muscle. While I am sure there are more than enough obese people running around that need to pay attention to their nutrition and exercise, there are also quite a few healthy specimens in the United States who likely have more muscle than the average citizen worldwide, thus erroneously placing the US in the obesity category more than it should be.

    A much more relevant body measurement is bodyfat % which can be accomplished quite accurately with a set of calipers available online. A bodyfat caliper tells you how much fat you have in proportion to your weight. They cost around $10 for the simple version and around $25 for a digital version that does all the math for you.

    I wish journalists and health organizations would stop using BMI as a descriptor. It is a misleading measurement and often an outright lie when referring to health.

  • Gene Girard

    Anyone who remembers a bit of high school geometry can look at the BMI formula and immediately become suspicious. The volume of three-dimensional objects grows as a function of the cube of radi, not the square. Is it a better proxy for body fat percentage than the Rohrer index (also known as the Ponderal index) which does use a cube function? I don’t know. My guess is they probably both suffer from the same problems as illustrated in the last post regarding differing muscle/fat ratios.

    That the BMI is the best we can do instead of starting out with, for example, cellular respiration, is baffling to me. It makes you want to throw up your hands and proclaim “I am an endomorph, leave me alone.”