Nurses Health Study Links Dietary Glycemic Load with Cardiovascular Risk Factors

A study by Liu et al. strengthens the evidence that glycemic load, a measure of carbohydrate intake, can predict cardiovascular disease (CVD) risk, especially in those who are insulin resistant.

Recent recommendations for the replacement of dietary fat with carbohydrates may not be as heart-healthy as previously thought, because high carbohydrate consumption can raise fasting plasma triacylglycerol concentrations and reduce high-density lipoprotein (HDL)-concentrations.

The association between glycemic load and higher CVD risk seen in this group of postmenopausal women may be less strong in groups who are younger, leaner and more active, and thus have a lower degree of insulin resistance.

Participants were part of the Nurses Health Study, established in 1976 and originally consisting of 121,700 female registered nurses who have been followed up every 2 years since inception of the study.

A subsample of 280 postmenopausal nurses, aged 45-70, were not taking hormone replacement therapy and were considered healthy. Serum samples were analyzed for HDL and triacylglycerols, and dietary intake was measured with a semiquantitative food-frequency questionnaire.

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Carbohydrate quality, or ability to raise blood sugar, was determined as each foods glycemic index, which was then multiplied by the frequency of consumption of that food to arrive at an overall glycemic load for each subject. When glycemic load was divided into quintiles of intake, a comparison of the two extreme quintiles revealed a significant relationship between higher glycemic index, higher serum triacylglycerol and lower serum HDL levels.

Fasting triacylglycerol was 76% higher among those with the highest glycemic load, 17% higher with increasing overall glycemic load and 44% higher with increasing carbohydrate intake. HDL concentration decreased 10% with increased glycemic load, 11% with increasing glycemic index and 4% with increasing carbohydrate intake.

These results establish the relevance of glycemic load as a potential risk factor for CVD in the Nurses Health Study cohort, and the authors maintain, this connection should be investigated in other populations as well. Although HDL and triacylglycerols respond to dietary factors other than carbohydrate intake, glycemic index can serve as a "gold standard" for the prediction of CVD risk because it provides an objective and independent measure of physiologic response.