Mitchel L. Zoler, PhD
February 04, 2021
Adults who eat three slices of white bread daily have a significantly increased risk for dying from cardiovascular causes.
That's one finding from an assessment of more than 137,000 people in 21 countries that documented a clear link between a high level of consumption of refined grains and a significantly increased risk for death from any cause or major cardiovascular disease (CVD) event during a median follow-up of 9.5 years.
The results showed that people who reported eating at least 350 g (seven servings) of refined grain daily had a significant 29% increased risk of either death or a major CVD event (MI, stroke, or heart failure), compared with those who consumed less than one serving per day (fewer than 50 g) of refined grain after adjustment for multiple potential confounders, according to a report from the Prospective Urban Rural Epidemiology (PURE) study published in the BMJ on Feb. 3, 2021.
The analysis also showed no significant association between levels of whole grains or white rice in the diet and CVD events. Rice was considered a separate grain in the analysis because nearly two-thirds of the PURE study population reside in Asia, where rice is a staple food.
The findings show that "reduction in the quantity of refined grains and sugar, and improvement in the quality of carbohydrates is essential for better health outcomes, although we do not suggest complete elimination of refined grains," said Mahshid Dehghan, PhD, lead investigator for this report and a researcher in nutrition epidemiology at the Population Health Research Institute of McMaster University, Hamilton, Ont.
'Widely Applicable' Results From Large, Diverse Study
Although prior evidence had already shown the CVD risk from eating larger amounts of refined grains, "our findings are robust and more widely applicable because our large study recorded over 9,000 deaths and 3,500 major CVD events across a broad range of refined grain intake, and in a variety of different settings and cultures with varying dietary patterns," Dehghan said in an interview.
"This is an important paper, with the strength of data from diverse countries. The associations are robust," commented Dariush Mozaffarian, MD, DrPH, professor and dean of the Friedman School of Nutrition Science and Policy at Tufts University, Boston, who was not involved in the new report.
"The public and the public health community think about added sugar in food as harmful, but starch has gotten a free pass," he said in an interview. Recently revised U.S. dietary guidelines recommend that refined grains constitute less than half of a person's carbohydrate consumption, but that limitation remains set too high, Mozaffarian cautioned. A much safer daily consumption limit would cap refined grains to no more than one serving a day.
The data for the current PURE analysis came from more than 148,000 people aged 35-70 years at entry in 21 geographically and economically diverse countries. Excluding patients with known CVD at baseline left a cohort of 137,130 people.
The results showed no significant association between the quantity of whole grains consumed and the main outcome, nor a link between higher amounts of white rice consumption and the main outcome.
"Our findings suggest that intake of up to 350 g of cooked rice daily may not pose a significant health risk," said Dehghan.
Refined Grains Produce a Glucose Surge
Dehghan and associates speculated that possible explanations for their findings are that "varieties of rice such as long-grain rice and especially parboiled white rice may have both a definite glycemic advantage and an overall nutritional advantage over refined wheat products. Also, depending on the culture and the nature of the rice eaten, rice may be displacing less desirable foods."
In contrast, refined grains undergo "rapid action by digestive enzymes and quick absorption from the small intestines [that] could lead to an increase in postprandial blood glucose concentrations. The rise in glucose concentrations increases the insulin concentrations, which leads to hypoglycemia, lipolysis, and the stimulation of hunger and food intake," the authors wrote.
"It's similar to eating sugar, or candy," noted Mozaffarian, as refined grain "is 100% glucose." Whole grains differ by entering the gut packaged in cell structures that slow digestion and avoid delivering sugar in an unnaturally rapid way.
"We are providing new evidence, and we hope that dietary guidelines in North America encourage individuals to lower their refined grain and sugar intake," Dehghan said.
PURE has received partial funding with unrestricted grants from several drug companies. Dehghan had no disclosures. Mozaffarian has been an adviser to or has received personal fees from several food companies, but had no relevant disclosures.