You raise a complicated question for which there is currently only a partial answer at best. Yes, genes associated with obesity have been identified, but they don’t necessarily make you fat. What’s more, there seem to be a lot of these genes, and their expression may be modified by many factors, including what you eat.
I addressed this subject recently when I reported on a study from the Harvard School of Public Health showing that a genetic predisposition to obesity doesn’t mean that those affected will inevitably become overweight or obese. The researchers found that some of these people can gain weight faster than others as a result of eating fried food and that people with a higher genetic risk of obesity may face a double whammy: the genetic predisposition may lead to more weight gain as a result of eating fried food, and the food itself may magnify the genetic effects.
The study also showed that the genetic effect on body mass index (BMI) among study participants who ate fried foods more than four times a week was about twice what it was in those who ate them less than once a week. The study found no link between a high genetic risk and increased intake of calories, suggesting that obesity genes may have more influence on how quickly (or slowly) individuals burn calories than on the amount of calories they consume.
As for exercise, we know even less about its genetic influences than we do about the genetic effect on weight. You may have read about genetic tests said to determine whether or not you’ll benefit from exercise. Only one of these tests is regarded as reliable. It is based on scientific findings from the UK showing that some people who take up jogging or another type of aerobic exercise respond to it quickly and increase their fitness, while others don’t. After studying genotyped muscle tissue from volunteers who had completed six to 20 weeks of endurance training, the investigators found that about 30 variations in how genes were expressed have a significant effect on how fit the study volunteers became. This test won’t tell you everything about the way exercise affects you – it reveals only how it impacts your lungs’ ability to absorb and distribute oxygen to the muscles involved in the effort. However, based on genetic variations picked up by the test, some participants learned that they would respond quickly to endurance training, and some learned that they are “low responders” to aerobic exercise and won’t get much out of it.
But even here, the genetics of exercise don’t tell us everything we need to know about the effects of working out. The authors of the 2010 gene study reckoned that the gene profile they identified accounts for at least 23 percent of the variation in how we respond to endurance training. That leaves another 77 percent that we may be able to influence. If you don’t do well with endurance training, you might have more success with strength training, for instance. However, it is early in the evolution of this new knowledge. If you’re not getting the effects you expected from exercise, don’t give up yet. Future studies may reveal what you can do to get more out of your workout.
Andrew Weil, M.D.
Li Qi et al, “Fried food consumption, genetic risk, and body mass index: gene-diet interaction analysis in three US cohort studies.” BMJ 19;348:g1610.
J.A. Timmons, “Using molecular classification to predict gains in maximal aerobic capacity following endurance exercise training in humans.” Journal of applied physiology, June 2010 doi: 10.1152/japplphysiol.01295.2009.