White Bread or White Rice? Glycemic Index Telling of CVD Risk Across Borders

Across the world, consumption of foods with a high glycemic index was a predictor of cardiovascular disease (CVD) and death, researchers reported from an observational study.

Compared with people eating foods with a low glycemic index, those eating higher-ranking carbohydrates were at greater risk of CVD events, such as CV death, MI, stroke, and heart failure, and all-cause mortality over a median 9.5 years of follow-up.

This was true whether study participants had preexisting CVD at baseline (adjusted HR 1.51, 95% CI 1.25-1.82) or not (adjusted HR 1.21, 95% CI 1.11-1.34), according to David Jenkins, MD, PhD, of the University of Toronto, and colleagues in the PURE group.

These findings have implications for both primary and secondary prevention strategies, the investigators suggested in the New England Journal of Medicine.

Less marked were the results according to glycemic load — a better measure of a food’s effect on blood sugar taking into account how quickly it enters the bloodstream and how much glucose can be delivered — as only people with preexisting CVD showed an association between diets with high glycemic load and patient outcomes.

The study was notable for including people from various economic and geographic backgrounds. Participants were recruited from four high-income countries, 11 middle-income countries, and five low-income countries on five continents starting in 2006.

As such, the study “permits an examination of the association between glycemic index and glycemic load with events across a very broad range of dietary patterns,” in contrast to previous data that had been mostly collected in high-income Western populations, Jenkins’ group said.

The study included 137,851 adults, with clinical outcomes data available for 119,575 of them.

Participants completed country-specific questionnaires asking how often, on average, during the previous year they ate a particular unit of food. From their responses, investigators estimated dietary intake, glycemic index, and glycemic load.

Food was grouped into seven categories with assigned glycemic indices based on food frequency averages: non-legume starchy foods (93), sugar-sweetened beverages (87), fruit (69), fruit juice (68), non-starchy vegetables (54), legumes (42), and dairy (38).

Foods with high glycemic index were consumed most in China, followed by Africa and Southeast Asia. Southeast Asia had diets with highest glycemic load, followed by Africa and China.

“As expected, a higher glycemic index was associated with an increased risk of adverse effects among the participants with a higher BMI, as reported previously,” Jenkins’ group reported. “Although the glycemic index of foods is independent of glucose-tolerance status, the overall postprandial glycemic response to diet increases as the BMI increases.”

The authors cautioned that grouping foods into seven categories likely resulted in less precision in glycemic calculations. However, they maintained that their method has shown reasonable correlation with glycemic index values generated by individual food calculations.

Other limitations include a sample that was not large enough to compare findings by geographic region and the reliance on diet assessment at a single point in time.

“For example, we began recruiting participants in China at a time when carbohydrate intakes were higher than they are now. More rapid changes in dietary patterns are likely to be seen in populations, such as those in China, that have had rapid economic growth,” Jenkins and colleagues said.

“Nevertheless, the data from the present study have proved sufficiently consistent to show dietary associations with disease outcomes,” they stated.