Losing weight if you’re overweight can help improve your health in many ways. But it can also take a toll on your bones. For example, a large observational study in the Journal of Bone and Mineral Research in 2018 found that, among 1,361 people, those who lost at least 5 percent of their body weight in recent years or over the long term had lower bone density and greater deterioration in bone microarchitecture than those whose weights were stable—and the association was stronger at weight-bearing parts of the skeleton. Whether intentional or unintentional, weight loss may have these adverse effects possibly due to decreasing mechanical load on bones as body mass decreases, hormonal changes, or decreased nutrients, such as protein, when fewer calories are consumed.
Can something be done to counteract this diet-related bone loss? Yes. Another study in the Journal of Bone and Mineral Research, published in December 2019, suggests that if you’re on a weight-loss diet—especially if you’re an older adult—you should make time for resistance (strength) training in addition to stepping up your aerobic exercise.
The study included 160 obese adults ages 65 and older (about two-thirds of them women) who were randomly assigned to a weight-management program plus one of three supervised exercise regimens: aerobic exercise (walking on a treadmill, stationary cycling, or stair climbing), resistance training (using weight-lifting machines), or both, done for an hour, three times a week. A fourth (control) group did not follow a weight-loss or exercise program but instead attended monthly educational sessions about a healthful diet.
After six months, participants in the three exercise groups had lost a comparable amount of weight: about 20 pounds on average, or 9 percent of their starting weight, compared with less than two pounds in the control group. But those who did resistance training, either alone or combined with aerobic exercise, had smaller losses in bone density at the hip than the group that did aerobic exercise only—0.7 percent and 1.1 percent in the resistance training and combination groups, respectively, vs. 2.6 percent in the aerobics-only group. (Changes in bone density at the other sites measured, namely the forearm and spine, were not significant.) The resistance exercisers also had smaller increases in blood markers of bone turnover (an indicator of osteoporosis risk).
The researchers concluded that “both resistance and combined aerobic and resistance exercise can be recommended to protect against bone loss during weight-loss therapy of older adults with obesity.” The best aerobic exercises for building and maintaining strong bones—to do in combination with resistance training—include running, jumping rope, and stair climbing. If you can’t do such high-impact workouts, gentler activities such as walking and low-impact aerobics are also good. (Swimming, cycling, and other nonimpact exercises are least beneficial for bones.)
To protect your bones, be sure to also eat a healthy diet that includes adequate calcium, vitamin D, magnesium, and other bone-essential nutrients, and take calcium and vitamin D supplements if your diet falls short in these two nutrients.