Research news from Tufts University, Friedman School of Nutrition Science and Policy: April 2004

April 02, 2004

Bones are Boosted by High Protein Diets

The latest weight loss fad, the high protein/low carbohydrate diet, has been the source of much criticism from the nutrition community. While many nutritionists agree that the diet may not be nutritionally balanced, one concern, that high protein diets promote calcium losses , may not be warranted.

Recent research by Bess Dawson-Hughes MD and her colleagues at the Bone Metabolism Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University shows that high protein (and reduced cereal grain) diets do not affect urinary calcium excretion, rather, the protein may decrease bone resorption, a process that make bones stronger.

The study, published in the March issue of The Journal of Clinical Endocrinology & Metabolism, looked at men and women over 50 who were randomized to either a high or low protein intake diet and who were already including the recommended 800 milligrams of calcium in their diet. The researchers found that those who increased their dietary protein by an average of 58 grams of protein a day had 25 percent higher levels of bone growth factor and lower levels of a marker of bone resorption compared with controls. Both these factors indicate healthy bone status.

While this study did not confirm the perception that high protein diets result in calcium loss, Dr. Dawson-Hughes cautions, "this study does not support the high protein, low carbohydrate approach to weight loss. There are many nutrients that contribute to healthy bones and a balanced diet, rich in fruits, vegetables, whole grains and protein is one of the best ways to ensure healthy bones throughout a lifetime."

Dawson-Hughes et al, The Journal of Clinical Endocrinology & Metabolism, 89:1169-1173. "Effect of Dietary Protein Supplements on Calcium Excretion in Healthy Older Adults."

The Power of Soy is in the Protein

Soy products have long been touted as one dietary food group that may help lower risk of heart disease. In the most recent edition of the Journal of Nutrition, researchers at the Jean Mayer USDA Human Nutrition Center on Aging on Tufts University showed that soy protein may lower LDL, also known as the bad cholesterol, a small amount, possibly contributing to decreased risk of heart disease in other ways.

In the past it had been suggested that soy's potency may come from the high amounts of plant based compounds, called isoflavones. This promising concept was refuted in a recent Tufts paper, and also confirmed by other studies, showing that contrary to popular belief, the plant based soy isoflavones do not lower cholesterol.

As soy has been shown to be beneficial to decreasing heart disease risk, Tufts researchers led by Alice H. Lichtenstein DSc, senior scientist and director of the Cardiovascular Nutrition Laboratory, examined the effect of the protein in soy on the particle size of LDL. A larger LDL particle size is associated with lower risk of heart disease. In order to determine the effect of soy protein, as part of a diet, on LDL particle size, the researchers examined the outcome of soy protein diets, either enriched or depleted of soy isoflavones compared to common sources of animal protein, either with added isoflavones or without.

They found that people who ate diets high in soy protein significantly increased their LDL particle size compared to periods when they were provided with diets high in animal protein. The isoflavones did not contribute to either type of protein's effect on LDL particle size. The potential cardiovascular benefits were seen in women who had a mean soy protein intake of 55 grams a day and men who had a mean soy protein intake of 71 grams a day, an amount that can be obtained from eating soy based foods such as meatless burgers, sausages and patties as a main entrée once daily.

Desorches, S., Mauger, J., Ausman, L., Lichtenstein, A.H.,& Lamarche, B., The Journal of Nutrition, 134:574-57, March 2004. "Soy Protein Favorably Affects LDL Size Independently of Isoflavones in Hypercholesterolemic Men and Women."
The Gerald J. and Dorothy R. Friedman School of Nutrition Science and Policy at Tufts University is the only independent school of nutrition in the United States. The school's eight centers, which focus on questions relating to famine, hunger, poverty, and communications, are renowned for the application of scientific research to national and international policy. For two decades, the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University has studied the relationship between good nutrition and good health in aging populations. Tufts research scientists work with federal agencies to establish the USDA Dietary Guidelines, the Dietary Reference Intakes, and other significant public policies.

Tufts University

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