A recent study by Dr. David J. A. Jenkins, published in the New England Journal Of Medicine, demonstrated that the glycemic index of the diet is directly associated with the risk of cardiovascular disease and death. This study was conducted in multiple countries and the results were similar across various economic and geographic regions.
The glycemic index of a food item is defined as the increase in the blood sugar level from 50 grams of carbohydrate of that food item. Carbohydrate foods with low fiber content and a high proportion of refined grains to whole grain ratio usually have a high glycemic index, such as white bread and white rice. Avoidance of poor quality carbohydrate foods and beverages that have a high glycemic index is a strategy for the prevention and treatment of diabetes. However, whether this approach can also be applied in the prevention of cardiovascular disease (CVD) requires more evidence, especially in non-western societies where the data in this matter is lacking. Prospective Urban Rural Epidemiology (PURE) study was conducted to address this question.
The PURE study included 137,851 participants from countries with various economic statuses across the world. The demographic and physical assessment of the participants as well as the information on the habitual food intake were collected via standardized and country-specific questionnaires. The participants were categorized based on their previous medical history of cardiovascular disease and were divided into quantile groups of glycemic load and glycemic index based on food questionnaires. The glycemic load is calculated by multiplying the mean net carbohydrate intake of the food item (in grams) by glycemic index and then dividing by 100. The primary and secondary outcome was defined as individual cardiovascular events or death from any cause. The multivariable Cox frailty models were used to analyze the association between the glycemic index and the outcomes of interest.
The study included a mean follow-up of 9.5 years. Among 119,575 participants, the primary composite outcome occurred in 11.77% of the participants. A total of 8,252 participants experienced at least one of the composite outcomes. When comparing the lowest and highest glycemic index quantiles, participants with higher glycemic index were at a higher risk of major cardiovascular events regardless of history of preexisting cardiovascular disorders (participants with CVD at baseline hazard ratio: 1.51; 95% confidence interval [CI]: 1.25-1.82; participants with no CVD at baseline hazard ratio: 1.21; 95% CI:1.11-1.34). Similarly, an increase in glycemic load was associated with a higher risk of major cardiovascular events and death. However, this association was only significant among those with a previous history of CVD. Interestingly, among participants with a higher body mass index (BMI ≥ 25), the association between glycemic index and risk of cardiovascular disease was more remarkable.
It is important to acknowledge that there are some limitations that should be considered while interpreting the results of this study. First, carbohydrate values were calculated based on the seven categories rather than the type of food itself, which might have decreased the real association with a particular food. Second, the inclusion of a diverse population might decrease the uniformity of the conclusion. Third, the sample size was not large enough to allow meaningful association in some geographic regions.
In conclusion, data from this study showed a diet containing foods with a higher glycemic index was associated with a higher risk of cardiovascular disease and death when compared to a diet containing lower glycemic index foods.