Researchers analyzed participants in five continents to determine the association between glycemic index and cardiovascular disease.
The glycemic index is how much 50 grams of carbohydrates raise blood glucose, depending on the food eaten. Previous data has shown the benefit of a low glycemic index diet in the prevention and treatment of diabetes. Low glycemic index diets have been associated with lower postprandial glucose levels, lower serum cholesterol levels, and lower blood pressure, reducing diabetes and cardiovascular disease (CVD). Studies have also shown the benefits of high-fiber and whole-grain foods on chronic disease prevention. However, there is not enough data to determine an association between low glycemic index foods and CVD. Furthermore, previous studies regarding CVD have only been conducted in Western countries, limiting generalizability to low-income patients in non-Western countries. The Prospective Urban Rural Epidemiology (PURE) study was a large, international study that included participants from 20 countries over five continents to assess the cardiovascular impact of glycemic index and glycemic load.
The PURE study included 137,851 participants aged 35 to 70 years old from four high-income countries, eleven middle-income countries, and five low-income countries. A questionnaire with 3,200 food items was used to record each participant’s food intake. The “bread scale” was used to define the glycemic index, with white bread being 100. Analysts measured each patient’s glycemic load by multiplying the average net carbohydrate intake by the glycemic index and dividing it by 100. The primary outcome for the study was a composite of major cardiovascular events or death from any cause. Researchers conducted a subgroup analysis according to economic region, geographic region, sex, BMI, smoking, and exercise status to determine if there were differences in the association. Foods with the highest glycemic index were consumed by participants in China, Africa, and Southeast Asia.
Over a median of 9.5 years of follow-up, the primary outcome occurred in 14,075 participants, death occurred in 8,780 participants, and at least one major cardiovascular event occurred in 8,252 participants. There was a positive association between the primary outcome and high glycemic index among patients without pre-existing CVD (HR 1.21, 95% CI 1.11 – 1.34) and patients with pre-existing CVD (HR 1.51, 95% CI 1.25 – 1.82). A higher glycemic index was also associated with an increased risk of death from cardiovascular and non-cardiovascular causes. However, for high glycemic load, a positive association was only seen for major cardiovascular events and death in those with pre-existing CVD. Among the subgroups, a more significant association was seen among participants with a BMI greater than 25 (P = 0.01). Higher economic areas had stronger associations to the primary outcome (HR 1.93, 95% CI 1.05 – 3.53).
This study’s weakness is the grouping of foods into glycemic index categories, which may have affected the precision depending on food variability. Due to the variety of foods from all over the world, it was difficult for researchers to assign a value to each food item accurately. Another weakness was the inability to periodically assess diet changes that may have been altered during the study’s duration and affected results. In contrast, this study’s strengths included participants from many countries with varying diets and income statuses, allowing for generalizability. Furthermore, this study emphasized glycemic index and glycemic load influence in predicting cardiovascular disease and mortality risk. Clinicians should educate patients on the impact of their diet choices and provide healthy alternatives. Overall, results showed that patients consuming diets with a low glycemic index and load were at a lower risk of developing cardiovascular disease and death.
- High glycemic index foods are associated with an increased risk of cardiovascular disease and mortality across many regions with varying diets and economic status.
- Diets high in the glycemic index may increase postprandial glucose levels in patients with an increased BMI, further strengthening cardiovascular disease risk.
- Implementing a high-fiber and whole-grain diet reduces cardiovascular disease and mortality in patients with and without pre-existing cardiovascular disease.
Jenkins DJA, Dehghan M, Mente A, et al. Glycemic Index, Glycemic Load, and Cardiovascular Disease and Mortality[ 2021 February 24]. N Engl J Med. 2021;10.1056/NEJMoa2007123.
Brand-Miller J, Hayne S, Petocz P, Colagiuri S. Low-glycemic index diets in the management of diabetes: a meta-analysis of randomized controlled trials. Diabetes Care 2003;26:2261-7.
Macrina Ghali, PharmD Candidate 2021, Florida A&M University, College of Pharmacy and Pharmaceutical Sciences