Women who eat a low-carbohydrate, high-protein diet may be increasing their risk for heart disease and stroke, a new study suggests.

There were about four or five extra cases of cardiovascular problems per 10,000 women who were studied as they followed  Atkins-type diets, say researchers. They called the findings directly relevant to young women who often resort to restricting carbohydrates and boosting protein.

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Despite the popularity of low carb, high-protein diets, clinicians should probably advise against following them for lont-term control of weight. (Albert Gea/Reuters)

"Although low carbohydrate-high protein diets may be nutritionally acceptable if the protein is mainly of plant origin [such as nuts and soy] and the reduction of carbohydrates applies mainly to simple and refined ones, the general public do not always recognize and act on these qualifications," Pagona Lagiou of the University of Athens Medical School and her co-authors said in this week's issue of the British Medical Journal.

Lagiou's team analyzed nutritional data on 43,396 Swedish women aged 30 to 49 who were followed for an average of 15 years.

In that time, 1,270 cardiovascular events such as heart attacks and strokes were recorded.

The researchers estimated that every 20-gram decrease in daily carbohydrate intake, like a small bread roll, and five-gram increase in protein per day, such as a boiled egg, would increase overall risk of cardiovascular disease by five per cent.

Factors likely to influence the results were taken into account, including smoking, alcohol use, diagnosis of hypertension, overall level of activity and saturated unsaturated fat intake.

Investigators assessed participants' diets when the study began and grouped them into tenths based on carbohydrate, protein and low carb plus high protein intake.

Cardiovascular disease risks

The possible benefits of low-carb diets for controlling weight or insulin resistance in the short term need to be investigated further, the study's authors said.

In the context of previous research, the Swedish study further challenges the safety of following a low carb, high protein diet long term, Anna Floegel from the German Institute of Human Nutrition and Tobias Pischon from the Max Delbrück Center for Molecular Medicine in Berlin said in a journal editorial.

The observational findings seem biologically plausible in that low carb diets are usually low on wholegrain foods, fruits and starchy vegetables that offer fibre, vitamins and minerals. A high protein diet may include higher intake of red and processed meat with iron, cholesterol and saturated fat, the editors said.

Earlier this month, another study of Swedes suggested that low-carb, high-fat diets could be to blame for their high cholesterol levels.

"Despite the popularity of these diets, clinicians should probably advise against their use for long term control of body weight," the editorial concluded.

"The short term benefits of low carbohydrate-high protein diets for weight loss that have made these diets appealing seem irrelevant in the face of increasing evidence of higher morbidity and mortality from cardiovascular diseases in the long term."

The  study was funded by the Swedish Cancer Society and the Swedish Research Council.