Some women may get more benefit than others from doing the same type of exercise, and genes are part of the reason why, a new study finds.

Women in the study who had certain genetic markers gained weight after following a strength-training regimen for a year, whereas women who didn't have those markers lost weight after following the same regimen, researchers said. The researchers looked at genes that have been linked in previous studies with an increased risk of obesity.

The findings may mean that women whose genes predispose them to obesity need to do more exercise to get their desired weight-loss results, and may also need to pay more attention to their diet, said study author Yann C. Klimentidis, an assistant professor of epidemiology and biostatistics at the University of Arizona in Tucson.

"There is just a higher wall to climb if you have a high genetic predisposition [for obesity]," Klimentidis said. However, he noted that "exercise is good [for your health] in lots of ways, not just body composition and weight."

In the study, the researchers examined DNA samples from 84 women ages 30 to 65, focusing on genes linked with obesity. The investigators asked all the women to engage in high-intensity resistance exercise and moderate-impact exercise with weights for at least one hour, three days a week, for a year. To analyze the effects the exercise had on the women, the researchers grouped them based on their genetic risk of obesity. [Lose Weight Smartly: 7 Little-Known Tricks That Shave Pounds]

The researchers found that exercise had a greater effect on both weight loss and body fat in the women whose genetic risk of obesity was lower, compared with the women whose genetic risk was higher.

For example, women whose genes put them at a high risk of obesity gained an average of 2.6 lbs. (1.2 kilograms) during the study period, whereas women whose genes put them at a low risk of obesity lost 2.9 lbs. (1.3 kg), on average.

In addition, the researchers found that women whose genes put them at a high risk of obesity maintained the same percentage of body fat over the study period, whereas women whose genes put them at a low risk of obesity lost 2.7 percent of their body fat, on average.

The study shows that "the benefit that one might get from exercise is going to depend on their level of the genetic risk [of obesity]," Klimentidis said.

The body mass indexes (BMIs) of the women at the beginning of the study ranged from 19 (normal) to 33 (obese). The women were told not to change their diets for the duration of the study.

It is not clear how genes associated with BMI may affect the impact of exercise on weight and body composition, the researchers said. One possibility is that these genes may interact with exercise through physiological mechanisms such as satiety, taste and regulation of energy expenditure.

But it's also possible that people who have a low genetic risk for obesity may also respond differently to doing more exercise, in terms of how much they eat and how much energy they expend, compared with those with a high risk, according to the study.

More studies should be conducted to help identify the mechanisms that may be involved in the link, the researchers said.

The new study was published today (April 30) in the International Journal of Obesity.

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