Dieters And Bone Loss

In 1992 a North Dakota physiologist made a connection between weight loss and bone loss in an ongoing study of the relation of dieting to bone content.

In a five-month study of fourteen overweight women, aged 20 to 40 years, in a weight reduction program, Dr. Henry C. Lukaski of the Grand Forks Human Nutrition Research Center found that the women lost one to two percent of their bone mass along with an average of eighteen pounds of weight.

The weight reduction program was specifically designed to prevent bone loss: the diet contained adequate amounts of all essential vitamins and minerals and more than the recommended 800 milligrams of calcium per day; the women also participated in a supervised aerobic exercise program lasting two hours each day. After one month on a maintenance diet, the study participants’ caloric intake was reduced by 25 percent for the next month and by 50 percent for the last three months, to an average of 1,200 to 1,300 calories a day.

When their caloric intake was cut in half, the women lost bone faster and formed new bone more slowly than normal. The study also found that the women retained less than normal amounts of magnesium, a mineral involved in bone growth.

Dr. Lukas said that the relationship between weight loss and loss of bone has been generally ignored in this country. He also said that there are many questions concerning weight and bone loss that need to be answered. For example, is there a connection between bone content and body weight? If the same amount of weight is lost in a short period of time versus a longer period of time, is the bone loss greater, less, or the same? Is there a benefit of increased muscle mass in preventing bone loss? Is bone mass restored when lost weight is regained? If it is not, those who lose and gain weight in the infamous yo-yo cycle may be at greater risk for osteoporosis than previously thought.

Ballerinas And Osteoporosis

There have been epidemiological studies whose conclusions support Dr. Lukaski’s clinical study correlating bone loss with dieting. The New England Journal of Medicine published a study (5/22/86) which found that nearly a quarter of 75 female ballerinas surveyed at four major ballet companies had some degree of scoliosis. Since scoliosis afflicts only 3.9 percent of white females in this age range, the rate of scoliosis in the corps de ballet (which was all white) was more than six times the normal. The study also found that dancers with scoliosis were more likely to have eating disorders (bulimia and anorexia) than others:

” Dancers are known to diet to maintain the thin body form that is considered ideal in classical danceThe dancers in our study weighed a mean of 87 percent of the ideal value. Those with scoliosis also scored higher on the oral control scale, which is a measure of dietary behaviorThe incidence of anorexia nervosa in ballet dancers is 5 percent to 22 percent, a reflection of dieting behaviorCalcium and vitamin D intake is suboptimal among ballet dancers, and the effects of this deprivation could lead to inadequate calcification, osteopenia, and poor skeletal stability.”

It would appear that the curved spines and stress fractures of these young ballerinas are manifestations of the same osteoporosis that afflicts many postmenopausal women, taking a somewhat different form in youth than in middle or old age: “Scoliosis and fractures may be adolescent manifestations of inadequate calcification and skeletal stability during a rapid growth phase: However, this osteoporosis of youth, even if asymptomatic at the time of onset, as it might be in young women who diet to a less intense degree than those who develop scoliosis and fractures, might be the precursor of the osteoporosis of later life: “Pubertal apposition of bone may be decreased so that at the time of maturation, bone density is lower than normal. Thus, loss of bone at even a normal rate could result in a mechanically incompetent skeleton and fractures.”

It could be argued that it is the intense physical exercise involved in the training of young ballerinas rather than the intense dieting which often accompanies such exercise that is the real cause of the weakened bones. However, weight-bearing exercise is known to increase bone mass. It is more probable that the exercise is a compensating factor which is not, however, sufficient to offset the deleterious effect of malnutrition. The authors of the study are of the opinion that: “the findings in the sample are especially surprising because extensive physical training of the type in which ballet dancers engage may have a protective effect on the skeleton and prevent bone loss. The studies suggest that the stress associated with regular strenuous exercise may not be sufficient to compensate for the loss in estrogen or dietary deficiencies at a crucial stage.”

Anorexia Nervosa And Osteoporosis

To establish definitively whether the bones of the ballerinas were weakened by exercise or dietary deficiencies, a study of bone density in a population of anorexics who are not also ballerinas would be needed. Fortunately, such a study has been done. “Osteoporosis in Women With Anorexia Nervosa,” also reported in The New England Journal of Medicine (12/20/84), involved a study of 18 anorexic women around the age of 25: “Our results demonstrate that women with anorexia nervosa have a significant reduction in critical bone density in comparison to controls of normal weightWe believe that the decreas ed bone density represents osteoporosis. The clinical consequence of decreased bone density was manifest in two patients who had multiple vertebrae compression fractures with back pain and loss of height before the age of 25.” Their conclusions support the hypothesis of the ballerina study that it is malnutrition rather than strenuous exercise that is responsible for the loss of bone mass. In fact, their data confirm the protective effects of exercise on bone mass: “Patients reporting a high level of regular exercise had a significantly greater bone density than less active patientsFurthermore, the mean bone density of highly active patients did not differ from that of active or sedentary controls, suggesting that exercise may be protective.”

The authors of the study go on to make the connection between malnutrition due to anorexia nervosa in adolescence and postmenopausal osteoporosis: “Young women who have an episode of anorexia nervosa during adolescence may not attain their potential peak skeletal mass and may have a lower bone density than age-matched normal subjects in early adulthood. Loss of bone mass may occur in addition to failure of bone developmentAfter the menopause, when the rate of bone loss accelerates, women who have recovered from anorexia may be at an increased risk for osteoporotic fractures of the hip, vertebrae, and wrist.”

It is reasonable to hypothesize, then, that the epidemic of osteoporosis in postmenopausal women in this country might very well be the result of chronic long term dieting, which though not as severe as that of anorexia nervosa, takes its toll over the years, finally manifesting its damage in the same symptoms at mid-life that afflict anorexic women in their mid-twenties. The studies reported in these articles were based upon a population of young girls at the start of their reproductive lives who yet displayed the brittle bones and curved spines of osteoporotic women at the end of theirs. The malnutrition brought about from dieting could well be the common cause of the brittle bones of the ballerinas and the elderly women in walkers.

Mary Lou Williams, M. Ed., is a lecturer and writer in the field of nutrition. She welcomes inquiries. She can be reached at (239) 267-6480.