A diet which decreases fat and increases carbohydrate is frequently prescribed for preventing cardiovascular disease (CVD). According to a new study in The American Journal of Clinical Nutrition, the decision to substitute carbohydrates for fats should take into consideration the type of carbohydrate chosen since the wrong choices may put an individual at greater risk of CVD. When ranked by their glycemic index, carbohydrates are markedly different in how quickly they cause blood sugar to rise. While many carbohydrates such as rice and potatoes have high glycemic indices and cause a dramatic rise in glucose and insulin 2 or 3 hours after eating, others such as beans and legumes break down more slowly and produce a more gradual rise in glucose and insulin in the bloodstream. An individual's glycemic load is based on the carbohydrate content of each food measured by its glycemic index, multiplied by the frequency of consumption of that food. In their study, Liu et al. of Harvard Medical School found that women with the highest glycemic load had an increased risk of coronary heart disease.
The research followed 75,521 female nurses ages 38-63, with each participant filling out a detailed food frequency questionnaire at baseline, two years later, and six years later. Seven hundred sixty-one cases of fatal and nonfatal CVD occurred during the ten year course of the study. The women were grouped in quintiles according to their overall dietary glycemic index, glycemic load, and overall carbohydrate intake. After adjusting for other lifestyle and risk factors, women in the highest quintile for glycemic load were 1.57 times more likely to have CVD than women in the lowest quintile. The increased risk of CVD associated with high glycemic load was most evident among women with a body mass index greater than 23, in other words those of average or above-average weight.
The authors conclude that the traditional classification of carbohydrates as simple sugars or complex starches is not useful in measuring an individual's risk of CVD. According to the authors, their data concerning the importance of the glycemic index "add(s) to the concern that the current low-fat, high-carbohydrate diet recommended in the United States may not be optimal for the prevention of CVD and could actually increase the risk in individuals with high degrees of insulin resistance and glucose intolerance."
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Liu, S et al. A prospective study of dietary glycemic load, carbohydrate intake, and risk of coronary heart disease in US women. Am J Clin Nut 2000;71:1455-1461.
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