People who lift weights every day may accumulate less belly fat over the years than people who spend the same amount of time doing aerobic exercises, according to a new study.
Combining weight training and aerobic activity, which is particularly beneficial for heart health, would be optimal, the researchers said.
“When we age, we lose muscle mass and we tend to accumulate more body fat. If you only engage in aerobic activities, such as running, jogging, you will end up losing fat as well as muscle mass,” said study co-author Rania Mekary, a researcher at the Harvard School of Public Health. “That’s why you need to supplement your workout with resistance training, in order to preserve the muscle mass.”
However, that is not to say that aerobic activities are less important for health, Mekary emphasized. Doing cardio exercises may help prevent conditions such as diabetes, heart disease and even cancer, she said.
The study looked at 10,500 healthy American men age 40 and older. Specifically, the researchers examined participants’ weight, physical activity and waist circumference to see how changes in the men’s activity levels over 12 years affected their waistlines. For older adults, waist circumference is a better indicator of healthy body composition than is body mass index, the researchers said.
Men’s waist sizes tend to increase as they age, and the men in the study showed a 1.2-inch increase in their waists, on average. But the men who engaged in weight training for 20 minutes a day had a smaller increase than men who spent the same amount of time doing aerobic exercises, according to the study. The results held after controlling for other factors that affect weight, such as diet.
The researchers also found that the men who increased their sedentary behaviors, such as watching TV, had a larger increase in their waistlines than those who didn’t increase sedentary time, according to the study, which was published in the journal Obesity.
“Engaging in resistance training or, ideally, combining it with aerobic exercise could help older adults lessen abdominal fat while increasing or preserving muscle mass,” Mekary said. Although the study was limited to men, the researchers suspect that the results are true for women as well, she said.
Some previous studies have found that aerobic exercises work better than weightlifting for people who are trying lose belly fat. But those studies looked at the effects over shorter terms, often over several months.
A phenomenon called excess post-exercise oxygen consumption may explain why people in the study gained less fat over the years if they engaged in weight training, Mekary said. To burn fat, the body needs oxygen, and with weight training the body’s metabolic rate remains high up to two days after exercise, resulting in more burning of fat.