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New Data on Dietary Protein and Bone
By Rosalie Marion Bliss
April 28, 2003
A high-protein diet containing mostly meat did not have adverse effects on women's ability to retain calcium in a study conducted by Agricultural Research Service scientists in Grand Forks, N.D.
ARS researchers Zamzam (Fariba) Roughead and Janet Hunt at the Grand Forks Human Nutrition Research Center controlled the diets of 15 healthy postmenopausal women, providing both low- and high-meat diets for eight weeks each. The women consumed about 600 milligrams (mg) of calcium per day, half the recommended intake of 1,200 mg. Calcium, sodium and caffeine intakes were kept constant.
In recent years, scientists have theorized that high-protein diets leach calcium from bones, leading to bone loss, based on findings from tests involving purified proteins. But unlike purified proteins, meat contains substantial amounts of potassium and phosphorus, which reduce urinary calcium loss. About 200 million people worldwide are affected by the bone thinning known as osteoporosis.
In the study, after the first four weeks of each eight-week phase, the scientists tracked calcium levels using body count technology that detects differences in calcium retention and excretion. The scientists found that even with low-but-average calcium intake, the volunteers could eat twice the recommended dietary allowance of protein, mostly as meat, and not have an adverse effect on calcium retention or on biomarkers for bone breakdown.
The high-meat diet consisted of 20 percent of daily calories as protein, or about 117 grams, including 10.5 ounces of meat. The low-meat diet consisted of 12 percent protein, including 1.5 ounces of meat. While eating as much as 35 percent of daily calories as protein is considered safe, the study was designed to give no more than 20 percent of daily calories as protein to ensure that volunteers consumed a varied diet.
The study was published in the April issue of the Journal of Nutrition.
The scientists next will launch confirmational studies, including one to corroborate other findings that high-protein diets, in combination with the recommended 1,200 mgs of daily calcium, may benefit bones.
ARS is the chief scientific research agency of the U.S. Department of Agriculture.