When it comes to high protein diets and health, the source of the protein really does matter, new research suggests.

After following nearly 30,000 women for 15 years, investigators found that women were more likely to die from heart disease if they often substituted red meat for carbohydrates. In contrast, swapping vegetable sources of protein for carbs appeared to protect women from heart disease.

“Our main finding was that animal compared to vegetable sources of protein seem to have a different effect on dying from heart disease,” study author Dr. Linda E. Kelemen from the Mayo Clinic College of Medicine in Rochester, Minnesota told AMN Health.

For this reason, she recommended that people who want to follow high protein diets should stick with vegetable proteins such as tofu, nuts and peanut butter, or healthier meats like chicken or fish.

With high protein diets a now-popular eating style, few studies have examined their long-term health effects, and whether different sources of protein make a difference, Kelemen and her team write in the American Journal of Epidemiology.

To investigate, the researchers interviewed 29,017 postmenopausal women about their eating and lifestyle habits, then followed them for 15 years, noting who died and of what cause. All of the women were free of cancer, heart disease and diabetes at the beginning of the study.

The investigators found that women who most often ate vegetable protein in place of carbohydrates and animal protein were 30 percent less likely to die of heart disease.

But the more red meat and dairy products women substituted for carbohydrates, the more their risk of heart disease increased.

Overall, opting for protein over carbs had no significant influence on the risk of dying from any cause.

Kelemen explained that it’s still unclear why our hearts like vegetable proteins better than animal proteins. It’s possible that vegetable proteins contain different building blocks, minerals or antioxidants that are good for our bodies, Kelemen said. Vegetable proteins could also contain substances that affect hormones in healthier ways, she added.

“Protein from different sources seems to have different health effects,” she noted. “Long-term adherence to higher protein intakes without distinguishing between the source of the protein may increase the risk of dying from heart disease.”

SOURCE: American Journal of Epidemiology, February 2005.