Older women who fit more minutes of heart-pumping exercise into their week will lose more body fat, a new study shows.
Canadian researchers found that postmenopausal women who got five hours of moderate-to-vigorous aerobic exercise every week -- double the normally recommended amount -- lost significantly more body fat within a year than women who exercised less.
"More is better. That's definitely what we found here," said study author Christine Friedenreich, a scientific leader in the department of cancer epidemiology and prevention research at Alberta Health Services-CancerControl Alberta, in Calgary. "If you can do more, you will do better."
The U.S. National Institutes of Health currently recommends that adults get at least two hours and 30 minutes of moderate-intensity aerobic activity every week, the authors noted in background information.
Previous research has shown that exercise does decrease body weight and total body fat, Friedenreich said, but her research team wanted to know whether increasing a person's "dose" of exercise would produce even better results.
To test this theory, the researchers recruited 384 women whose body mass index (BMI) ranged from 22 to 40. A BMI under 25 is considered healthy, while 30 or more is considered obese. All women were disease-free, nonsmokers and were not taking hormone replacement therapy.
Half of the women were asked to exercise the recommended minimum amount of two hours and 30 minutes a week, while the other half had to exercise for five hours a week.
The women could take part in any aerobic activity they liked, as long as they kept their heart rate within 65 percent to 75 percent of their heart rate reserve for at least half of each exercise session. Most activities involved an elliptical trainer, walking, bicycling or running. Heart rate reserve is the gap between a person's resting and maximum heart rate.
"It's not light activity," Friedenreich said of the exercise required. "It's something that definitely causes an increase in your heart rate."
Researchers measured each woman's body fat before and after, using X-rays and CT scans, to track their progress after a year's worth of exercise.
The investigators found that the women who got the minimum amount of exercise did experience improvements in weight and BMI and, on average, lost body fat.
However, women who doubled their exercise regimen experienced significantly more reduction in BMI and total body fat. They also lost more belly fat, and their waist circumference and waist-to-hip ratio decreased significantly more.
The findings were reported in the July 16 online edition of JAMA Oncology.
Body fat has been linked to increased breast cancer risk, because fat produces the female hormone estrogen and also increases insulin resistance and inflammation, Friedenreich pointed out.
"It's been very clearly shown that if you gain weight over your lifetime and if you are overweight after menopause, that increases your risk of breast cancer," she said.
Alpa Patel, an epidemiologist with the American Cancer Society, said "these results allow us to say that there's this much benefit if you exercise the minimum 150 minutes recommended, and there's this much more benefit added if you can get that to 300 minutes."
In this study, the women were asked to maintain their usual diet, Friedenreich said.
Women can achieve even greater weight loss and fat reduction if they pair an increase in exercise with a healthy diet, said Kerri Winters-Stone, a research professor at the Oregon Health & Science University School of Nursing, in Portland.
Other studies have shown that combining diet and exercise can provide better weight loss results than either diet or exercise on their own, said Winters-Stone, who wrote a commentary that accompanies Friedenreich's study.
"It really boils down to an energy balance equation," she said. "You can get there quicker by changing diet and exercise, rather than trying to achieve it by exercise alone."
Winters-Stone added that increasing exercise is a good idea, but people need to make sure they understand their own physical limitations. Overuse injuries can occur if a person heedlessly pursues a stringent exercise regimen.
"People can kind of reach their max," she said. "Overexercise tends to exacerbate knee pain, for instance, or it might cause an old shoulder injury to flare up."