If you are genetically prone to obesity there is one type of exercise that could be of special help. It’s jogging. And if that’s not your thing, yoga comes in a close second.
These are the findings of a study of more than 18,000 Han Chinese, led by Wan-Yu Lin of the Institute of Epidemiology and Preventive Medicine at the National Taiwan University in Taipei, Taiwan.
It’s an irksome statistic for people trying to lose weight, but body mass index (BMI) – that’s your weight in kilos divided by height in metres squared – is to a large extent inherited. Up to 81% of the variation in BMI between folk is explained by their lineage.
That means obese people, who have a BMI of 30 or more, can thank their genes for a good part of their predicament.
But as the biology mantra runs, both nature and nurture figure in the final outcome, and exercise has already been shown to limit the genetic effect on BMI.
Good news. But, as Lin and colleagues point out, there are a range of other obesity measures that are as important, or even more so, than BMI as a predictor of illness.
Waist circumference, hip circumference and waist-to-hip ratio give a measure of central obesity, the spare tyre that accumulates around the midriff.
Lin’s team wanted to find out whether exercise, and indeed which kinds, could offset not just the genetic risk of raised BMI, but central obesity as well.
So they headed to the Taiwan Biobank, which has amassed data on the genes and lifestyle of more than 20,000 Taiwan residents aged 30-70, including the aforementioned obesity measures plus their body fat percentage.
The Biobank also stores info on participants’ preferred regular exercise – defined as 30 minutes three times a week – ranging across 18 pursuits such as jogging, yoga, mountain climbing, cycling, swimming and a computerised dancing game called dance dance revolution.
The researchers zeroed in on genetic variations among the study’s 18,424 participants and used them to calculate a genetic risk for each of the obesity measures. Then they factored in each person’s exercise habits to work out which ones might be working against that genetic destiny.
It’s worth noting here that they calculated genetic risk for Taiwanese locals precisely because existing risk scores done in Europeans might not apply to them. Hence, their results could be less valid for other ethnic groups.
Nevertheless, jogging emerged as a clear winner. A regular leg stretch limited the genetic effects on BMI, body fat percentage and hip circumference. Mountain climbing, vigorous walking, standard dance and longer versions of yoga blunted the genetic effects on BMI alone.
And there were some surprising losers. Neither cycling nor swimming (nor indeed dance dance revolution) put the brakes on genetic risk towards any of the obesity measures.
The authors offer up some tentative reasons for why that might be so. Cycling is among activities that, they write, “usually require less energy expenditure than the six exercises that demonstrate interactions with genetic risk score.”
And for swimmers in the audience, the researchers point to studies suggesting that exercise in cold water can trigger increased appetite and food intake.
Their overall conclusion does not, however, call out any form of exercise as a damp squib.
“Our findings show that the genetic effects on obesity measures can be decreased to various extents by performing different kinds of exercise. The benefits of regular physical exercise are more impactful in subjects who are more predisposed to obesity.”
The study appears in the journal PLOS Genetics.
Paul Biegler is a philosopher, physician and Adjunct Research Fellow in Bioethics at Monash University. He received the 2012 Australasian Association of Philosophy Media Prize and his book The Ethical Treatment of Depression (MIT Press 2011) won the Australian Museum Eureka Prize for Research in Ethics.
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