High Glycemic Diets Increase Cardiovascular Disease and Death Risk

David Jenkins (St. Michael's Hospital)

A new study found that a diet with a high glycemic index is associated with an increased risk of cardiovascular (CV) disease and death, particularly in large, geographically diverse populations. 

Investigators, led by David Jenkins MD, PhD, DSc of the University of Toronto, conducted the study to determine dietary intake and estimate the glycemic index in specific patient populations where prior data has not been collected.

The team uncovered outcomes showing patients who consumed a diet with a low glycemic index and glycemic load had a lower risk of CV disease compared to participants who consumed a diet with a higher glycemic index and glycemic load. 

The association between glycemic index rates and cardiovascular disease as well as all-cause mortality was collected in the International Prospective Urban Rural Epidemiology (PURE) study.

The Study

Jenkins and team hypothesized the study data would show the relationship between the glycemic index marker determining carbohydrate quality and chronic disease, focusing on cardiovascular disease.

The study included 137,851 participants from 20 countries, between the ages of 35-70 and included a median of 9.5 years of follow-up.

According to investigators, the 20 countries included 4 high-income countries, 11 middle-income countries, and 5 low-income countries.

Participants were classified into 7 regions: Europe and North America, South America, Africa, Middle East, South Asia, Southeast Asia, and China.

The team used standardized questionnaires to collect data on demographic factors, socioeconomic status, lifestyle, health history and medication use. Data on physical assessments included weight, height, waist and hip circumference, and blood pressure. 

Baseline data collection information on the food frequency of individuals with 28 questionnaires, of which 19 were specific to individual countries and 9 were specific to regions in India. 

A total of 3200 food items were included in the questionnaires and investigators used of 98 - 220 items per questionnaire. Participants were asked to clarify how often on average they had consumed the food item, ranging from “never” to “6 or more times per day”.

The team assigned a glycemic index to 7 categories of carbohydrate-containing food and were then weighted according to the net carbohydrate consumed in each food category. This data determined the participant’s mean glycemic index, and a multivariable Cox frailty model was used to calculate hazard ratios. 

Investigators’ primary outcome was a composite of a major CV event including CV death or nonfatal myocardial infarction or death from any cause. 

The Results

Follow-up data on primary outcomes of a major CV event was available for 119,575 participants and data on major cardiovascular events was available for 119,572. 

Investigators found the primary composite outcome occurred in 14,075 participants, with 8780 deaths discovered. In the same time period, 8252 participants had at least 1 major CV event. 

In comparisons of the highest to lowest glycemic index quintiles, investigators found diets with a high glycemic index had an increased risk of a major CV event or death, both in patients with and without preexisting CV disease.

The findings in glycemic load were similar to the index findings but did not affect those without preexisting CV disease.

Investigators also found individuals with a higher body mass index (BMI) had a higher risk of adverse effects. As BMI increases, a person with a high glycemic index may also experience an increase in postprandial glycemic response and cause insulin resistance. 

Diet may also lead to diabetes or CV death and increase the risk of death of other causes, possibly including COVID-19, investigators wrote.

“Our study showed that in a diverse population of participants, those who consumed a diet with a low glycemic index and a low glycemic load had a lower risk of cardiovascular disease and death than participants who consumed a diet with a higher glycemic index and glycemic load,” investigators wrote.

The study, “Glycemic Index, Glycemic Load, and Cardiovascular Disease and Mortality,” was published online in The New England Journal of Medicine.