No Heart Risk for Women Who Favor Protein Over Carbs

BOSTON, Nov. 8 -- Women who say no to carbs, but yes to protein as recommended in the South Beach and Zone diets, do not increase their risk of coronary heart disease, according to researchers here.

And women who consume low-carbohydrate diets that emphasize vegetables rather than animals as the source of protein and fat may be rewarded with a moderate reduction in risk of heart disease.

So it emerged from the Nurses' Health Study, a longitudinal study of 82,802 women who have been followed since 1976.

Women whose diets consisted mainly of vegetable protein and fat were are about 30% less likely to develop coronary heart disease than women who whose diets contained either more carbohydrates or more animal protein and fat (P for trend=0.002), Thomas L. Halton, Sc.D. of the Harvard School of Public Health, and colleagues reported in the Nov. 9 issue of the New England Journal of Medicine.

There was a significant direct association between dietary glycemic load and coronary heart disease (relative risk, 1.90; 95% CI, 1.15 to 3.15; P for trend= 0.003), they wrote.

Moreover, the overall dietary glycemic index had a direct association with the risk of coronary heart disease (relative risk 1.19; 95% CI, 0.91 to 1.55, P for trend=0.04).

They added that total fat, animal fat, total protein, animal protein, and vegetable protein were not significantly associated with the risk of coronary heart disease according to multivariate analysis.

Dr. Halton and colleagues from Brigham and Women's Hospital here and the UCLA School of Public Health collected information on diet form food frequency questionnaires that covered more than 120 specific foods and by weekly diet records collected in 1980 and 1986.

They divided the participants into 11 strata on the basis of on fat, protein, and carbohydrate intake expressed as a percent of total energy consumption. Women were then awarded points, 10 for those in the highest stratum of fat and protein intact and zero for those who consumed the lowest amount of fat and protein.

For carbohydrate consumption the scoring system was reversed, so that those with the highest carbohydrate intake received a zero, while those who consumed the lowest carbohydrates receive a 10.

As a result, the overall diet scores ranged from zero-for women who consumed a low-fat, low-carbohydrate diet-to 30, which was awarded to women who consumed a high-fat, high-protein, low-carbohydrate diet.

Additional scores were created for low-carbohydrate diets that calculated percentage of energy from vegetable protein or fat intake and percentage of energy form animal fat or protein.

Medical records were reviewed to assess the rate of coronary heart disease.

Among the findings:

• There were 1,994 new cases of coronary heart disease documented during 20 years of follow-up.
• The mean daily carbohydrate intake for women who had the lowest carbohydrate intake was 116.7 g versus 234.4 g for women with the highest carbohydrate intake.
• After 10 years follow-up, women who followed low-carbohydrate diets were more likely to smoke, had a higher body mass index, a lower dietary glycemic load, a lower caloric intake, and a higher intake of saturated fat.
• Low carbohydrate diets had no significant long-term effect on weight.

MaryAnn McLaughlin, M.D., M.P.H., medical director of the cardiac health program at Mount Sinai Medical Center in New York, said the study by Dr. Halton and colleagues was "an important addition to the ongoing debate as to what type of diet is best."

While noting that the study "is just observational, there were so many women followed for so many years that I do think this does move the science forward," said Dr. McLaughlin, who is an assistant professor at Mount Sinai School of Medicine.

She said it is likely that the benefit reported here reflects the lower glycemic index associated with low-carbohydrate diets.

And while there was no long-term weight loss, Dr. McLaughlin noted that the average BMI increased by 2.5 units over 20 years, which she said may be lower than the gain experienced by most women as they age. She said that it is not unusual for women to increase BMI by 5 units as they age.

But she cautioned that the study was limited by a lack of data about potential adverse effects of high protein diets such as "renal damage, osteoporosis and malignancy."

The authors acknowledged those limits and suggested the need for further study to assess potential adverse effects.

The National Institutes of Health and the American Heart Association supported the study. One of the authors, Simin Liu, M.D., Sc.D, acknowledged grant support from General Mills for a study on magnesium, and senior author Frank B. Hu, M.D., Ph.D., reported support from the California Walnut Commission for a study on alpha-linolenic acid.