Nov. 14, 1996
Eating less meat may help reduce osteoporosis risk, studies show
Want to reduce the risk of osteoporosis? Eat less meat, Cornell researchers say.
In fact, they say, reducing the amount of meat in the diet may do more to reduce the risk of osteoporosis than increasing calcium intake.
A series of studies from the Cornell-China-Oxford Project on Nutrition, Health and Environment, by nutritional biochemist T. Colin Campbell and his colleagues, conclude that reducing meat intake reduces the risk of losing bone density. Osteoporosis is a condition, usually associated with aging, in which bone density decreases, making people susceptible to breaks and fractures.
Whether dairy products offer protection from osteoporosis, however, is still undetermined, according to the researchers. If dairy products are consumed in a diet high in animal protein, any potential benefit for increased bone density would be undermined. That's because animal protein, including that from dairy products, may leach more calcium from the bones than is ingested, said Campbell, professor of nutritional biochemistry at Cornell and director of the Cornell-China-Oxford Project, the most comprehensive project on diet and disease ever conducted.
"This phenomenon could explain why Americans, who ingest much higher levels of calcium, have much higher rates of osteoporosis and hip fractures compared with many Chinese and other Asians who consume few dairy products and ingest low amounts of calcium," Campbell said. Hip fractures in the United States, for example, are approximately five times more frequent than in China.
Osteoporosis is a potentially disabling disease of later life in which the bones deteriorate and easily fracture; the disease affects 25 million Americans, 80 percent of whom are women.
Campbell, with Banoo Parpia, Cornell senior research associate on the China project, Ji-Fan Hu, a former graduate student at Cornell, and other Chinese collaborators analyzed the role of dietary calcium in bone density by following closely the diets of 800 women from five counties that have very different diets in China. The Mongolians in one county, for example, consume a nomadic diet of high meat and dairy protein with few vegetables and fruits; the Sichuan diet, on the other hand, is primarily vegetarian with only shavings of meat used for flavorings.
The researchers measured the women's food consumption for three days, collected information on bone density and calcium absorption and excretion from blood and urine tests, and then controlled for factors such as height, weight and age in their analysis.
Analyses of these data suggest that increased levels of animal-based proteins, including protein from dairy products, "almost certainly contribute to a significant loss of bone calcium while vegetable-based diets clearly protect against bone loss," Campbell reported.
This view is consistent with evidence comparing bone fracture rates among different countries, which shows that countries having the highest calcium intakes also have the highest fracture rates. It is also consistent with other studies on nutritionally rich "Western" diets and "Western" diseases showing that low-calcium, vegetarian diets are associated with increased bone density; that casein, milk's principal protein, is a well-established contributor to high blood cholesterol in the Western world; and that casein significantly enhances the development of tumor growth in experimental animals.
"Vegetarians obtain plenty of calcium and appear to have higher rates of bone density, which predispose them to lower rates of osteoporosis," said Campbell, who reported last year that Americans will not reduce their rates of cancer, cardiovascular disease and other chronic, degenerative diseases until they shift from an animal-based diet to a plant-based diet. Animal-based diets tend to be high in fat and low in fiber; plant-based diets are generally low in fat and high in fiber and other substances such as antioxidants, which are proving to be important in preventing cancer.
Campbell, Parpia and other co-authors published their findings in two articles of The American Journal of Clinical Nutrition (both 1993), the European Journal of Clinical Nutrition (1994), Osteoporosis International (1994), and more recently in the new book, Osteoporosis in Asia: Crossing the Frontiers, edited by E.M.C. Lau et. al (World Scientific Press) in a chapter called, "Diet, Calcium and Bone Density of Women in China."
Specifically, the studies found that:
- Diets high in animal and nondairy animal protein were linked to high urinary excretions of calcium, whereas plant-protein diets were linked inversely to calcium excretion (AJCN).
- Since women lose their bone mass at fairly consistent rates after age 40, women who had higher peak bone mass by that age tend to fare better in older age because they are starting at a higher baseline (AJCN).
- The methods the researchers used in weighing a household's food before consumption were reliable ways to assess food and nutrient intake (EJCN).
- Daily physical exercise helped protect bone health in both pre- and postmenopausal women (OI).
Parpia pointed out that the average 150-pound American male typically consumes about 95 grams of protein a day, about two-thirds of which he derived from a meat sandwich at lunch and a hamburger or other meat at dinner. The recommended dietary allowance for protein, however, is only 56 grams and Campbell, who has been studying animal protein and its link to cancer, cardiovascular disease and other chronic, degenerative diseases, suggests that this level of protein is adequate for good health and can be readily obtained by diets comprised of plant-based foods.
"Although dietary calcium intake is most often the focus of nutritional recommendations for osteoporosis, what's important is the calcium balance, not just calcium intake," Parpia stressed. "This is also another case in which just looking at a single nutrient does not tell the whole story. Rather, you have to consider the entire diet."
Campbell is director of the Cornell-Oxford-China Nutrition Project, a massive survey of more than 10,000 families in mainland China and Taiwan designed to study diet, lifestyle and disease across the far reaches of China. By investigating simultaneously more diseases and more dietary characteristics than any other study to date, the project has generated the most comprehensive database in the world on the multiple causes of disease.