Beef Fights Kidney Stones

May 3, 2001

New research indicates that animal protein can be included in the diet of individuals with, or at risk of developing, one of the most common forms of kidney stones. For the 10% of the U.S. population with calcium kidney stones or a genetic disposition to them, this discovery offers more flexibility in what has traditionally been a diet restricted from beef and other animal protein sources.

Published in the March 2001 edition of the Journal of the American Dietetic Association (JADA), the study compared diets with animal protein (beef) sources with plant protein sources (legumes, seeds, nuts and grains) at the same amount of total protein in people with a history of calcium kidney stones. The study was conducted by Linda K. Massey, Ph.D., R.D., professor; and Susan A. Kynast-Gales, Ph.D., R.D., research associate, food science and human nutrition, Washington State University, Spokane, WA. It was funded by beef producers through the beef checkoff.

"It's been widely touted in the medical literature that ‘animal protein' is bad for people with kidney stones because it increased urinary calcium more than plant protein. Animal protein contains about 10 percent more sulfur-containing amino acids which can slightly increase urinary calcium," said Massey. "However, only plant foods contain oxalate, the other half of the salt that forms kidney stones. This trade-off led me to the study because, overall, the diets with animal protein should be no different, or worse, than diets based on plant protein and any other kind of protein."

This study looked at calcium kidney stones, or those formed by calcium and oxalate (a salt found in many plant foods). Calcium and oxalate form an insoluble compound like a fine grain of sand. A kidney stone can form if the crystals of this compound stick to each other. Most of the stones remain small and flush out in the urine. However, there are many variables that can affect the formation of these stones – the source of dietary protein being just one factor. It should be noted that vegetarian diets usually contain more oxalate than omnivorous diets. This research suggests that to reduce risk of kidney stones, the amount of dietary protein should be kept at moderate levels, but the kind of protein - animal or plant – does not matter.

Massey and Kynast-Gales studied 23 subjects in a four-day, free-living adaptation period, followed by a two-day metabolic unit study. Each participant ate a balanced diet designed on Food Guide Pyramid recommendations in terms of food variety and serving sizes. With the exception of alternating plant and animal proteins, the diets were identical. The researchers concluded that balanced diets containing moderate amounts of either beef or plant protein are equally effective in reducing calcium oxalate kidney stone risk based on changes in urinary composition.

A grants program funding this and other nutrition research projects at academic institutions across the country is managed by the National Cattlemen's Beef Association (NCBA) on behalf of the Cattlemen's Beef Board and state beef councils. Dozens of other projects are currently addressing such issues as beef nutrients in healthy diets, as well as their role in childhood development; beef in weight loss diets; and the benefit to the diet of beef lipids, including conjugated linoleic acid (CLA).

"Doctors have been telling patients for years that ‘animal protein is bad for you' and that ‘you should cut out red meat,'" said Massey. "The fact is, people wouldn't stick to their diets because they simply like red meat."

Massey explained that her study contains evidence that elimination of beef from diets of individuals with this kind of special health need is not necessary, provided they are eating a sensible diet that meets dietary requirements. In the past, beef might have been excluded for individuals with calcium kidney stones or risks of developing this common type of kidney stone.

"This research should give hope to individuals with, or at risk of developing, kidney stones that they don't have to shift to a vegetarian diet," explained Massey. "Speaking as a health professional, the best advice, as always, is to eat a variety of foods in moderation and with balance, even if you have special health needs such as kidney stones."