Older women who eat a relatively large amount of protein from red meat or dairy products may have an elevated risk of dying from heart disease, the results of a large study suggest.

The findings, say researchers, call into question the long-term safety of high-protein diets -- at least the ones that don't distinguish the protein in steak and cream from that in tofu and nuts.

The investigators found that among more than 29,000 postmenopausal women, those who reported the highest intake of protein from red meat and dairy products had a roughly 40 percent higher risk of dying from heart disease over the next 15 years compared with women with the lowest intake of these foods.

The risk would seem to stem from the protein intake itself, according to lead author Dr. Linda E. Kelemen, because her group considered the subjects' overall diet -- including intake of fat, fiber and total calories -- and factors such as exercise, smoking and body weight.

The findings are published in the current issue of the American Journal of Epidemiology.

High-protein and fatty foods are staples of Atkins-style diets that shun carbohydrates such as white bread and pasta. Though these diets have been shown to spur weight loss and dips in blood cholesterol in the short term, many experts worry that if people stick with such a menu over time, it could spell trouble for the blood vessels and heart.

Although the new study looked at women's normal protein intake -- and not high-protein, low-carb diets -- it has implications for adherents to those weight-loss plans, said Kelemen, an assistant professor of epidemiology at the Mayo Clinic College of Medicine in Rochester, Minnesota.

"I think it's very relevant to them," she stated. First and foremost, Kelemen said, people should recognize that "not all proteins are equal," and replacing white bread and other highly processed carbs with steak and butter is not the way to go.

More healthful choices, according to Kelemen, include fish and chicken, which were not linked to heart disease mortality in this study.

Better still, perhaps, would be vegetable protein sources, such as beans, nuts, tofu and peanut butter; the study found that women with the highest intakes of these foods had a 30 percent lower risk of heart disease death than women with the lowest intakes.

In contrast, the findings indicate that a woman who opts for two servings of red meat every day instead of a similar number of calories from carbs would have a 44 percent higher risk of dying from heart disease over the next 15 years. A similar pattern emerged when the researchers looked at dairy foods, including milk, cream, ice cream, yogurt and cheese.

Exactly why protein from red meat and dairy products might boost heart risks is unclear, and it's possible, Kelemen said, that factors not captured in this study could explain the association.

However, she noted, there is animal research showing that protein from animal sources, independent of fat and cholesterol content, can promote artery-clogging plaques. Soy protein, on the other hand, showed no such effects.

SOURCE: American Journal of Epidemiology, February 1, 2005.