The statistics on overweight and obesity for the United States population are staggering, and weight loss programs are being prescribed and attempted by ever-increasing numbers. While most weight loss programs tend to recommend a combination of diet and exercise for the best results, many people are still attracted to the idea of losing weight without exercise. Are they making a serious mistake and putting their bone health at risk?
It has long been known that losing weight can also lead to losing bone strength, because bone density tends to decline along with body weight. This increases the risk of osteoporosis—a particular concern for older people, who are highly vulnerable to bone fractures.
What was not known for certain, however, was whether losing weight through exercise was also associated with loss of bone density.
Calorie Reduction- Or Exercise-Induced Weight Loss?
A group of researchers at Washington University School of Medicine in St. Louis, MO, set out to test the hypothesis that exercise-induced weight loss leads to less bone loss than calorie-reduction-induced weight loss. Their report appeared in the December 2006 Archives of Internal Medicine: “Response to Caloric Restriction–Induced Weight Loss or Exercise-Induced Weight Loss: A Randomized Controlled Trial,” by Dennis T. Villareal; Luigi Fontana; Edward P. Weiss; Susan B. Racette; Karen Steger-May; Kenneth B. Schechtman; Samuel Klein; John O. Holloszy.
The Washington University Study
The study group included 48 adults: 30 women and 18 men, average age 59. Researchers divided the participants into three groups:
- Group 1 – 19 were placed on a graduated reduced-calorie diet, with energy intake reduced by 16 percent for 3 months, then by 20 percent for 9 months.
- Group 2 – 19 were placed on a graduated regimen of exercise to increase energy expenditure by 16 percent for 3 months and then by 20 percent for 9 months, with no reduction in calories.
- Group 3 – 10 were simply offered information on healthy lifestyles if they requested it.
Weight and bone density were measured at the start and then every 3 months. Blood tests were also taken at the start and at 6 and 12 months to see if bone tissue was being absorbed and regenerated.
At the end of the year-long study:
- Group 1 (restricted calories) lost 18.1 pounds on average and lost bone density in three high-risk locations: the lower spine (2.2%), the hip (2.2%), and the top of the femur (2.1%).
- Group 2 (exercise) lost 14.8 pounds, with no significant loss of bone density.
- Group 3 (information only) showed no change in weight or bone density.
In both group 1 and group 2, people who lost weight also experienced increased “bone turnover,” the process by which old bone is removed from the skeleton. However, in the exercise group—but not the calorie-restricted group—increased muscle action during exercise stimulated the creation of new bone material to compensate for that loss!
Dr. Villareal and the other researchers conclude that “Our results are consistent with an osteoprotective effect of exercise-induced mechanical strain on the skeleton and consequent increase in bone turnover.”
Dieting alone does lead to reduced bone density and risk of osteoporosis in areas of the body particularly prone to fractures, especially among older people. Losing weight through exercise does not have this effect, because exercise builds bones to compensate for the loss caused by calorie reduction.
These data strongly support the view that exercise is an important component of any weight loss program.