How much extra exercise you need to do to avoid obesity, based on your genetics
People who are genetically pre-disposed to putting on weight need to do twice as much exercise as those with the lowest genetic risk of obesity for the same result, a study shows.
It is well known that genes play a key role in obesity, with studies variously putting its contribution at 40 to 70 per cent of weight gain.
Now, for the first time, scientists have quantified what these genetic differences mean for the amount of exercise we need to do to keep our weight down.
Previous research has found that walking about 8,000 steps a day substantially reduces the risk of obesity. But that rough figure is only an average that doesn’t take into account a person’s “polygenic risk score” – or genetic risk of obesity.
Taking that as the starting point, researchers from the Vanderbilt University Medical Centre in Nashville followed 3,124 middle-aged European-descendant v participants – three quarters of them women, with an average age of 53 – for 5 years.
The participants, aged between 36 and 62, already owned a Fitbit device that measures steps and were without obesity – at the start of the trial – walking an average of 8,326 steps a day.
The researchers found that those who were in the top quarter of society for genetic obesity risk (based on a recognised measure) would need to walk 26 per cent further a day than those with an average risk.
That meant that those at highest genetic risk needed to walk 11,020 steps a day to have an even chance of becoming obese over five years – 2,280 more than those with an average risk of obesity, who needed to take 8740 steps for the same result.
But someone in the bottom quarter of genetic risk, would have the same 50/50 chance of obesity if they walked just 5,080 steps a day – 54 per cent fewer than those in the top quarter for risk and 3,660 fewer steps (40 per cent less) than the average person.
And while 10,000 steps a day may the generally accepted target we should all aim for, to have a good chance of avoiding obesity altogether, a person in the bottom quarter of risk for obesity would need to walk 11,000 steps a day and someone with an average risk would need about 13,600 steps a day, the findings indicate.
“I think it is intuitive that individuals who have a higher genetic risk of obesity might need to have more physical activity to reduce that risk, but what is new and important from this study is that we were able to put a number on the amount of activity needed to reduce the risk,” said lead author Evan Brittain, of Vanderbilt University.
“It is becoming more commonplace to know you have a genetic risk for obesity in the genomic era when genetic results are being returned directly to patients. And you can imagine a future in which that data could be integrated with someone’s electronic health record and could form the basis of an individual’s physical activity recommendation from their doctor,” he said.
The findings didn’t take into account non-genetic factors, most significantly the participant’s diet. This means that the results could potentially be skewed by other factors meaning a direct relationship between the effects of exercise and genetic obesity risk cannot be precisely quantified.
However, the researchers said they only recruited people who already owned a fitness tracking device and did not have obesity at the outset – of which 13 per cent with low genetic risk and 43 per cent with high genetic risk went on to develop obesity over the five years of the study.
More research is needed to see if the findings are replicated in diverse populations as the study only involved people of European ancestry, 95 of whom were white and just 5 per cent were of other race or ethnicity.
Dr Brittain added: “Current physical activity guidelines take a one-size-fits-all approach, and what we learned is that depending on your genetic risk, the guidelines may underestimate the amount of activity needed to reduce your risk of obesity.
“Most importantly, I would like for patients to know that your genetic risk doesn’t determine your overall risk of obesity, and you can actually overcome that risk by being more active.”
Stephen Lawrence, of Warwick University, who was not involved in the study, said it “should be considered important in terms of raising important hypothetical associations which may be more rigorously treated in a future study”.
“The ‘observational’ study design, while providing some insight into real-world data, hazards caution in over-interpretation. The focus on physical activity omits the crucial confounding factor of dietary intake. There is a pragmatic idiom that ‘you cannot exercise your way out of a bad diet”,” he said.
The study is published in the journal Jama Network Open
