People who mostly ate foods with a low glycemic index had a lower likelihood of premature death and major cardiovascular disease (CVD) events, compared with those whose diet included more “poor-quality” food with a high glycemic index.
The results from the global PURE study of nearly 120,000 people provide evidence that helps cement glycemic index as a key measure of dietary health.
This new analysis from PURE (Prospective Urban and Rural Epidemiological Study) – a massive prospective epidemiologic study – shows people with a diet in the highest quintile of glycemic index had a significant 25% higher rate of combined total deaths and major CVD events during a median follow-up of nearly 10 years, compared with those with a diet in the lowest glycemic index quintile, in the report published online on Feb. 24, 2021, in the New England Journal of Medicine.
David J.A. Jenkins, MD, PhD, DSc, lead author, said people do not necessarily need to closely track the glycemic index of what they eat to follow the guidance that lower is better.
The link between lower glycemic load and fewer CVD events was even stronger among people with an established history of CVD at study entry. In this subset, which included 9% of the total cohort, people in the highest quintile for glycemic index consumption had a 51% higher rate of the composite primary endpoint, compared with those in the lowest quintile, in an analysis that adjusted for several potential confounders.
A simple but accurate and effective public health message is to follow existing dietary recommendations to eat better-quality food – more unprocessed fruits, vegetables, legumes, and whole grains – Dr. Jenkins advised. Those who prefer a more detailed approach could use the comprehensive glycemic index tables compiled by researchers at the University of Sydney.
‘All carbohydrates are not the same’
“What we’re saying is that all carbohydrates are not the same. Some seem to increase the risk for CVD, and others seem protective. This is not new, but worth restating in an era of low-carb and no-carb diets,” said Dr. Jenkins.
Low-glycemic-index foods are generally unprocessed foods in their native state, including fruits, vegetables, legumes, and unrefined whole grains. High-glycemic-index foods contain processed and refined carbohydrates that deliver jolts of glucose soon after eating, as the sugar in these carbohydrates quickly moves from the gut to the bloodstream.
An association between a diet with a lower glycemic index and better outcomes had appeared in prior reports from other studies, but not as unambiguously as in the new data from PURE, likely because of fewer study participants in previous studies.
Another feature of PURE that adds to the generalizability of the findings is the diversity of adults included in the study, from 20 countries on five continents.
“This clinches it,” Dr. Jenkins declared in an interview.
New PURE data tip the evidence balance
The NEJM article includes a new meta-analysis that adds the PURE findings to data from two large prior reports that were each less conclusive. The new calculation with the PURE numbers helps establish a clearer association between a diet with a higher glycemic index and the endpoint of CVD death, showing an overall 26% increase in the outcome.
The PURE data are especially informative because the investigators collected additional information on a range of potential confounders they incorporated into their analyses.
“We were able to include a lot of documentation on many potential confounders. That’s a strength of our data,” noted Dr. Jenkins, a professor of nutritional science and medicine at the University of Toronto.
Dr. Salim Yusuf
“The present data, along with prior publications from PURE and several other studies, emphasize that consumption of poor quality carbohydrates is likely to be more adverse than the consumption of most fats in the diet,” said senior author Salim Yusuf, MD, DPhil, professor of medicine and executive director of the Population Health Research Institute at McMaster University, Hamilton, Ont.
“This calls for a fundamental shift in our thinking of what types of diet are likely to be harmful and what types neutral or beneficial,” Dr. Yusuf said in a statement from his institution.