
New Data on
Dietary Protein and BoneBy Rosalie Marion
Bliss April 28, 2003A 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. U.S. Department of Agriculture |