By Lisa Rapaport

(Reuters Health) – Obese adults who diet to lose weight may be able to protect against bone thinning with resistance exercise, a recent study suggests.

Weight loss efforts among obese adults are linked to an increased risk of thinning, brittle bones that are prone to fractures, the study team writes in the Journal of Bone and Mineral Research. While exercise can strengthen bones and reduce the risk of falls and fractures, doctors don’t yet know the optimal workout routine for obese people who are dieting.

For the current study, researchers randomly assigned 141 obese adults to one of four groups: dieters who did only aerobic exercise, dieters who only did resistance exercise, dieters who did both types of exercise, or a control group that didn’t exercise or diet. Dieters met with dieticians and did supervised workouts over 26 weeks, while the control group attended some education sessions on healthy eating.

People in all three diet groups lost about 9% of their body weight during the study, compared with 1% in the control group.

Bone density measured at the hip decreased less for the people who did resistance exercise alone or in combination with aerobic workouts than it did for others.

“When undergoing weight loss therapy, patients should incorporate as much as possible some resistance exercise to protect against bone loss,” said senior author Dr. Dennis Villareal of Baylor College of Medicine and the Michael E DeBakey VA Medical Center in Houston, Texas.

“Resistance exercise should be at least moderate in intensity,” Dr. Villareal said by email. “We do not know if less-intense exercise would be effective in protecting against bone loss during weight loss.”

Despite the health risks associated with obesity, weight loss programs for older adults can be risky because people can lose muscle mass and bone density as they slim down, the study team notes.

In the study, resistance exercise was associated with a smaller decline in lean muscle mass as well as smaller decreases in bone density than aerobic workouts.

Participants were 70 years old, on average, and all had a BMI of 30 or greater at baseline.

In the exercise groups, participants were given customized diets designed to create a deficit of about 500 to 750 calories a day. They also did supervised one-hour workouts three times a week.

Aerobic exercises included walking on a treadmill, riding a stationary bicycle, and stair climbing. Resistance exercises included upper- and lower- body exercises using weight machines. All of the exercisers also did some activities designed to improve balance and flexibility.

One limitation of the study is that researchers only followed people for about six months, too brief a time to determine whether one type of exercise might be better than another for fall or fracture prevention, the authors note.

“Based on this study, one would conclude that (for) an older adult who is obese and trying to lose weight, the combination of aerobic and resistance exercise will help the most to maintain their bone mineral density and their general physical fitness,” said Dr. Cynthia Brown of the Integrative Center for Aging Research at the University of Alabama at Birmingham.

“Older adults who are able should do muscle-strengthening exercises (resistance exercise) at least twice a week,” Dr. Brown, who wasn’t involved in the study, said by email. “It is recommended that older adults with multiple chronic conditions make sure they understand how these conditions affect their ability to exercise and all older adults should be as physically active as their abilities and conditions allow.”

SOURCE: Journal of Bone Mineral Research, online December 4, 2019.