Rethinking the role of protein-rich diets in osteoporosis prevention

Your mother probably told you to drink your milk because it’s good for your bones. For generations, a high-calcium, high-protein diet—with dairy and meat as the dietary centerpiece—has been recommended for good bone health.

But controversial evidence has emerged that suggests a high-protein diet with lots of dairy and meat products might actually promote the loss of bone mineral density, which can lead to osteoporosis. While the debate over how protein and other dietary components affect bone health continues to rage among medical experts, there are things you can do today to keep your bones healthy and strong.

Dietary Acids and Bone Health

Among the many nutrients that help to build your bones, calcium and protein are crucial to maintaining the cycle of bone resorption (break down) and formation that replaces worn bone with new, structurally sound bone.

Protein makes up about one third of the mass of bones, and a diet that is deficient in either calcium or protein is associated with a loss of bone mass, leading to osteopenia and, eventually, osteoporosis and fractures.

But beyond ensuring the strength of the skeletal system, protein and calcium also play an important role in regulating the delicate balance of acids and bases in the blood. When the blood becomes even slightly too acidic, calcium—which is alkaline—leaches from bone to neutralize the acids in the blood, a process that can lead to a reduction in bone mineral density.

The problem is that the typical American diet is high protein—rich in meat, poultry, fish, eggs, and dairy. When your body metabolizes these foods, they are broken down into sulfuric and organic acids that raise the acidity of the blood (digestion of cereal grains like rice and wheat also produce acidic compounds). Over a lifetime, chronic high levels of these acids may cause excessive leaching of the calcium in bone.

In fact, some experts hypothesize that the acidic nature of the Western diet may be contributing to the relatively high rates of osteoporosis in the United States and other industrialized nations. Other experts disagree, saying that the body compensates for this protein-induced loss of calcium from the bone by increasing the absorption of dietary calcium in the intestines. According to this theory, a high-protein diet will not affect bone health as long as calcium intake is sufficient.

The Importance of Fruits And Vegetables

Some researchers believe it’s not the amount of acid-forming, high- protein foods in the Western diet that contributes to osteoporosis, but rather the lack of acid-neutralizing foods, specifically fruits and vegetables. In contrast to high-protein foods, metabolism of fruits and vegetables produces alkaline compounds, especially bicarbonate, that neutralize acid levels in the blood and may reduce the leaching of calcium from bone.

In a randomized, controlled trial published in 2009 in the Journal of Clinical Endocrinology & Metabolism, 171 individuals over 50 years old received either a placebo or potassium bicarbonate, sodium bicarbonate, or potassium chloride for three months. Only the volunteers in the bicarbonate groups had a significant reduction in the excretion of calcium—a sign of loss of calcium from the bones. This finding led the researchers to surmise that higher levels of acid-neutralizing alkali in the diet may preserve bone mineral density.

Thus, combining a protein-containing diet with plenty of fruits and vegetables could help offset the possible loss of calcium from the bone. In addition, fruits and vegetables are high in potassium and magnesium—important components of healthy bone as well.

Animal or Vegetable?

Another school of thought argues that the type of protein consumed is important. Some studies suggest that protein from vegetable sources, including beans, peas, and other legumes, may promote bone health more than animal proteins.

In one study, published in the American Journal of Clinical Nutrition, researchers followed more than 1,000 women. After seven years, women who ate four times as much animal protein as vegetable protein were more likely to experience bone loss and fractures at the hip than women who ate nearly equal amounts of the two protein types.

Other studies have refuted this finding, showing that any source of protein is important to developing and maintaining bone health. Many of them, however, have been funded by the meat and dairy industries.

To Eat Protein or Not

A study currently under way at the Yale School of Medicine may help resolve some of the debate over the roles that protein and other dietary components play in osteoporosis. The Supplemental Protein to Outsmart Osteoporosis Now (SPOON) study will examine what effect, if any, protein supplementation has on bone health in women over age 60 and men over age 70. Results are expected later this year.

Until the results are published, your best nutritional bet to maintain the health of your bones is to get the recommended 1,000 to 1,200 mg of calcium daily—from milk or another calcium-rich source—and to eat a balanced, varied diet. For older adults, that means 6 oz of cereals, breads, rice, and pasta (at least half of which should be made from whole grains); 2.5 cups of vegetables; 1.5 cups of fruit; 3 cups of low-fat or fat-free milk, yogurt, or other milk products; and 5 oz of fish or lean meat or poultry.

Your intake of vitamin D is important, too. Aim for 400 to 1,000 IU per day, depending on your age.

Publication Review By: Lee H. Riley III, M.D., and Suzanne M. Jan de Beur, M.D.

Published: 18 Nov 2011

Last Modified: 05 Feb 2015