A group of European researchers led by Pagona Lagiou of the University of Athens Medical School in Greece assessed the diets of more than 43,000 Swedish women ages 30 to 49, and followed them for an average of almost 16 years. Women who consumed a diet consisting of low carbohydrate and high protein intake were at a 5 percent higher risk of cardiovascular disease later. By the end of the end of the study period, 1,270 women developed heart disease.
Consuming as little as 20 fewer grams of carbohydrates and 5 more grams of protein per day accounted for the increase, the researchers found.
The actual number of women who developed heart disease was small -- about four or five extra cases per 10,000 women per year -- but the authors said that amounted to a considerable number over time.
Data from other studies that evaluated the relationship between low-carb diets and the risk of cardiovascular disease have been mixed.
The Nurses' Health Study from 1991 found no association between a low-carbohydrate, high-protein diet and heart disease. Other more recent research, however, did find a link between these diets and a higher risk of cardiovascular disease.
But not all proteins are alike, which can make a difference in how heart-unhealthy this type of diet is.
"Low carbohydrate-high protein diets may be nutritionally acceptable if the protein is mainly of plant origin and the reduction of carbohydrates applies to simple and refined carbohydrates," the authors wrote.
One of the problems with Atkins-type diets is they are difficult to maintain, nutrition experts said. At the height of their popularity, there were also concerns that people who ate a lot of protein in the form of red meat and also ate very little fiber put themselves at risk for disease.
The goal of the once-popular diets, nutrition experts said, is short-term weight loss.
"These diets are not choice, but there have been some studies to show that a well-managed high-protein, low-carbohydrate diet in the short term can help an individual who needs to lose a large amount of weight," said Connie Diekman, director of university nutrition at Washington University in St. Louis.
Dr. Jana Klauer, a physician in private practice in New York, said she does recommend the diet for some people, but with an important caveat.
"A person who needs to lose weight can lose weight quickly, but it may not be such a good choice for people at risk for cardiovascular disease," she said. "If they did want to try a diet like that, they would want to be sure their source of protein is not fatty red meat, but fish."
However, in an accompanying editorial, German epidemiologists Anna Floegel and Tobias Pischon wrote that "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."
Diekman said the study does not identify a definitive link between low-carbohydrate, high-protein diets and heart disease, but it is a step toward identifying what impact these diets have on the heart.
"We need a really good study that analyzes food intake, follows up on food intake and looks at disease outcome," she said. The Swedish study, she said, used food questionnaires, which can be unreliable. The study also did not separate the effects of healthier proteins and carbohydrates.
The authors acknowledged the study's limitations, but stressed that the research sends an important message.
The findings, they wrote, "draw attention to the potential for considerable adverse effects on cardiovascular health of these diets when they are used on a regular basis, without consideration of the nature of carbohydrates (complex versus refined) or the source of proteins (plant versus animal)."
But Atkins Nutritionals Inc. released a statement criticizing BMJ for sending out a press release referring to the diets in the study as "Atkins-style." The study, they said, was not specifically of the Atkins Diet, which "emphasizes a healthy balance of proteins and good fats, and includes vegetables, fruits and even whole grains."
The Atkins Diet, said CEO Monty Sharma, is "a healthy, scientifically proven diet that includes healthy carbs, doesn't cut out any food groups, and is being passionately supported by millions of successful dieters across the globe."