TUESDAY, June 26 (HealthDay News) -- Women who regularly eat a high-protein, low-carbohydrate diet may be raising their risk of heart disease and stroke by as much as 28 percent, a new study suggests.

Although the absolute increase in risk is small -- four or five extra cases per 10,000 women -- many young women try the Atkins diet or similar regimens and could be setting themselves up for cardiovascular problems later in life, the researchers noted.

"Low-carbohydrate, high-protein diets are frequently used for body-weight control," said lead researcher Dr. Pagona Lagiou, assistant professor of epidemiology at the University of Athens Medical School in Greece. "Although [the diets] may be nutritionally acceptable if the protein is mainly of plant origin, such as nuts, and the reduction of carbohydrates applies mainly to simple and refined [carbohydrates] like unhealthy sweeteners, drinks and snacks, the general public does not always recognize and act on this guidance."

The study, published online June 26 in the BMJ, does not answer questions about the possible short-term benefits of these diets in the control of body weight or insulin resistance, Lagiou said.

For the study, Lagiou's team collected data on the diets of more than 43,000 Swedish women who were between the ages of 30 and 49 at the start of the study.

Over an average of 15 years of follow-up, there were more than 1,200 cardiovascular events, including heart disease and stroke. There were more of these events among the women who followed a high-protein, low-carbohydrate diet than among women who didn't, the researchers found.

Compared with women who veered furthest from the high-protein, low-carbohydrate diet, women who followed the diet most closely increased their risk by 28 percent, even after other risk factors, such as smoking, drinking, hypertension, exercise and fat intake, were taken into account, the researchers noted.

"Reduction of body weight should rely on increasing physical activity and reducing caloric intake," Lagiou said.

The long-term health effects of special diets that are followed for long periods of time have not been adequately studied to allow determination of their safety, she added.

Dr. Gregg Fonarow, chairman of cardiovascular medicine and science at the University of California, Los Angeles, said low-carb diets such as the Atkins regimen have been touted widely and have become increasingly popular.

"This study raises concerns about the long-term effects on cardiovascular health of low-carbohydrate, high-protein diets -- particularly if there is not careful consideration given to whether plant versus animal proteins are consumed," said Fonarow, who is also director of the Ahmanson-UCLA Cardiomyopathy Center.

For their part, Atkins Nutritionals Inc. says their diet plan differs greatly from the low-carb, high-protein diet used in the study.

"The diet tested had 51 percent carbohydrates, while the Atkins Diet begins at 10 percent carbohydrates, and increases to 20 percent 30 percent over several weeks as the dieter reaches and maintains target weight," the company said in a statement issued Wednesday.

The statement continues: "It appears that BMJ, to draw public attention to its story, misleadingly inserted the false suggestion that an 'Atkins-style' diet was used in the study, and omitted the conclusion of the Swedish researchers that diets similar to the actual Atkins Diet do not necessarily harm cardiovascular health. Atkins has demanded an apology and corrective action from the British Medical Journal."

Another expert, Samantha Heller, an exercise physiologist and clinical nutrition coordinator at the Center for Cancer Care at Griffin Hospital in Derby, Conn., said "the results of this study are not surprising."

Popular high-protein diets inevitably include an abundance of cheese and red and processed meats, and a dearth of healthy carbohydrates such as whole grains, vegetables, legumes and fruits, she said.

"What this study did not address is that research is finding that diets high in red meat and/or processed meats may increase the risk of type 2 diabetes; colorectal cancer; coronary heart disease; breast cancer; esophageal, liver and lung cancers; and chronic obstructive lung disease," Heller said. "[They also] increase levels of bad cholesterol."

More research is needed to pinpoint how and for whom these risks are elevated, she added.

"In the meantime, cut back on your intake of meat and other animal-protein sources. Start experimenting with beans, edamame, tofu, nuts and nut butters (such as peanut, almond and cashew butter), low- or nonfat yogurt, cottage cheese and milk," Heller advised. "Pick up the carb intake with 100 percent whole-grain breads, brown rice, quinoa and hefty doses of vegetables, legumes and fruits."

Although the study found an association between high-protein, low-carbohydrate diets and increased risk of cardiovascular problems, it did not prove a cause-and-effect relationship.

More information

For more on healthful eating, visit the U.S. Department of Agriculture.