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Monday, October 1, 2012


Consuming a low carbohydrate-high protein diet -- like the Atkins diet -- may be associated with a greater risk of cardiovascular disease in women, researchers found.
Decreases in carbohydrate intake and increases in protein intake, as well as in a score combining carbohydrate and protein intake, were all associated with significantly greater risks of incident cardiovascular disease events in young Swedish women, according to Pagona Lagiou, MD, PhD, of the University of Athens in Greece, and colleagues.
The findings, which were reported online in BMJ, "do not answer questions concerning possible beneficial short-term effects of low carbohydrate or high protein diets in the control of body weight or insulin resistance," the authors wrote.
"Instead, they 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)," they wrote.
Low carb-high protein diets have become popular because of the short-term effects on weight control, but concerns have been raised about the potential cardiovascular effects over the long term. Studies exploring the issue have given mixed results, with a U.S. study showing no relationship between such a diet and rates of ischemic heart disease.
But three European studies showed a greater risk of cardiovascular mortality with such a diet.
Lagiou and colleagues examined data from the Swedish Women's Lifestyle and Health Cohort, a prospective study conducted among women living in the healthcare region of Uppsala. The current analysis included 43,396 women, ages 30 to 49 at baseline, who completed a comprehensive questionnaire on lifestyle and dietary factors, as well as medical history. They were followed for an average of 15.7 years.
The researchers scored each participant according to their carbohydrate and protein consumption. Carbohydrate intake was scored from 1 (very high) to 10 (very low). Protein intake was scored from 1 (very low) to 10 (very high). A combined carbohydrate-protein score ranged from 2 (very high consumption of carbs and very low consumption of protein) to 20 (very low consumption of carbs and very high consumption of protein).
During follow-up, there were 1,270 incident cardiovascular events, which included ischemic heart disease, ischemic stroke, hemorrhagic stroke, subarachnoid hemorrhage, and peripheral arterial disease.
After adjustment for energy intake, saturated and unsaturated fat intake, and numerous cardiovascular risk factors, each one-point decrease in carb intake was associated with a relative 4% increase in cardiovascular events (95% CI 0% to 8%). A one-point increase in protein intake also was associated with a relative 4% increase in events (95% CI 2% to 6%).
Each two-point increase in the low carbohydrate-high protein score -- equivalent to a 20-gram decrease in daily carb intake and 5-gram increase in daily protein intake -- was associated with a relative 5% increase in cardiovascular events (95% CI 2% to 8%).
There was a suggestion that the associations were stronger for women whose protein came mostly from animal sources, but the test for interaction did not reach statistical significance for nearly all of the individual outcomes.
"Although these results are based on an observational study, their biological plausibility seems self evident," according to Anna Floegel, MPH, of the German Institute of Human Nutrition Potsdam-Rehbruecke, and Tobias Pischon, MD, MPH, of the Max Delbrück Center for Molecular Medicine Berlin-Buch.
"A low carbohydrate diet implies low consumption of whole-grain foods, fruits, and starchy vegetables and consequently reduced intake of fiber, vitamins, and minerals. A high protein diet may indicate higher intake of red and processed meat and thus higher intake of iron, cholesterol, and saturated fat," they explained in an accompanying editorial.
"These single factors have previously been linked to a higher risk of major chronic diseases, including cardiovascular disease, in observational studies, so it is not surprising that this combination of risk factors is linked to a higher incidence of disease and mortality," they said.
Lagiou and colleagues acknowledged that their study was limited by the possible misclassification of diet 
based on participant self-report only at the beginning of the study, the lack of information on cardiovascular medication use and blood cholesterol levels, and the possibility of residual confounding.
The study was supported by grants from the Swedish Cancer Society and the Swedish Research Council.
The study authors and the editorialists reported no conflicts of interest.
From the American Heart Association:

POSTED BY:  Steven Almany M.D.

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