Health News

High-Protein Diets Can Hurt Kidneys

March 17, 2003 -- High-protein diets like that of the popular Atkins diet may accelerate the loss of kidney function in people with early problems. However, these controversial diets do not seem to affect people with normal kidneys, suggests new research.

The problem is, as many as 20 million Americans are at risk for reduced kidney function but don't know it. Therefore, people on high-protein diets may be unknowingly damaging their kidneys.

"There are no symptoms attributable to this early kidney disease, but it's very prevalent," says Eric Knight, MD, MPH, lead researcher of the study and a doctor at Brigham and Women's Hospital in Boston. Those at highest risk are people with high blood pressure, diabetes, or are older than age 65, he says.

Even in his study, about one in four of the 1,624 women studied had mildly reduced kidney function that produced no obvious symptoms.

Knight's findings on high-protein diets are published in the March 18 edition of Annals of Internal Medicine. It's the latest chapter in the ongoing Nurses Health Study, which has already documented that frequent meat consumption may increase risk of colon cancer.

The women studied were questioned about their consumption of meat and other foods, and other health risks were also evaluated. They were tracked for 11 years, and researchers found that those with mild kidney problems who ate a high-protein diet --- especially protein from meat -- had a faster loss in function. No such association was noted among women with these kidney problems who got most of their protein from dairy foods. However, high meat consumption didn't seem to exacerbate problems in those with healthy kidneys.

"We saw a significantly measurable association in those consuming about 1.3 grams of animal protein for each kilo of body weight," Knight tells WebMD. "That level is not as high as the protein you get from animal sources in the Atkins diet. So clearly a person who is undertaking a high-protein diet such as Atkins should have a kidney function test and carefully be monitored while following this diet."

Are high-protein diets safe for those with normal kidney function?

"If the Atkins diet was the only way of losing weight, perhaps the benefits would outweigh the risks," he says. "Obviously, extreme obesity is a risk factor of kidney disease. But there are other health risks associated with high consumption of meat products, such as too much animal fats and saturated fats that increase the risk of heart disease. I think the message of our study is that people with mild reduced kidney function should be careful to moderate their intake of meat overall and very carefully consider the risk and benefits before starting an Atkins-type diet."

When beginning the Atkins plan, dieters typically eat about 2 grams of animal protein for each gram of body weight, says Colette Heimowitz, director of education and research for Atkins Nutritionals. That means a woman weighing 150 pounds would consume about 135 grams of protein each day -- nearly 40% more than what was typically consumed by those in Knight's study. In later stages of the high-protein diet, the amount of protein is reduced to levels consumed by those in Knight's study.