Higher refined grains intake ups risk of death, major CV events

People who regularly consume refined grains are at greater risk of death and major cardiovascular (CV) events, claims a study. On the other hand, eating whole grains or white rice shows no association with these clinical outcomes.

“Intakes of a combination of cereal grains with a lower intake of refined wheat products should be encouraged while promoting a higher intake of whole grains,” the researchers said. “Reduction in quantity and improvement in quality of carbohydrate is essential for better health outcomes.”

This prospective cohort study included 148,858 individuals from 21 countries, with a median follow-up of 9.5 years. Intakes of refined grains, whole grains, and white rice were assessed using country-specific validated food frequency questionnaires.

Major CV event was defined as death from CV causes, nonfatal myocardial infarction, stroke, or heart failure. Multivariable Cox frailty models were used to estimate hazard ratios (HRs) for associations of grain intakes with mortality, major CV events, and their composite, with random intercepts to account for clustering by centre.

Of the participants, 137,130 were included in the analysis, of whom 9.2 percent (n=12,668) had a composite outcome event during follow-up. [BMJ 2021;372:m4948]

The highest category of refined grains intake (≥350 g/day or about 7 servings/day) resulted in a greater risk of total mortality (HR, 1.27, 95 percent confidence interval [CI], 1.11–1.46; p_trend=0.004), major CV events (HR, 1.33, 95 percent CI, 1.16–1.52; p_trend<0.001), and their composite (HR, 1.28, 95 percent CI, 1.15–1.42; p_trend<0.001) compared to the lowest intake category (<50 g/day).

Higher consumption of refined grains also led to a higher systolic blood pressure. In contrast, no significant associations existed between intakes of whole grains or white rice and health outcomes.

Earlier studies have explored the association between refined grains intake and outcomes of all-cause and cause-specific mortality. A meta-analysis by Schwingshackl and colleagues reported no association of high vs low intake of refined grains with all-cause mortality, while previous cohort studies found an increased risk of coronary heart disease with higher consumption of refined grains. [Int J Clin Exp Med 2017;10:12749-12755; Am J Clin Nutr 2017;105:1462-1473]

Moreover, a review examining the association of bread consumption with obesity and abdominal fat showed that a reduction in white bread intake in a Mediterranean-style dietary pattern resulted in lower weight gain and abdominal fat gain.

“This might have happened as a result of a reduction in intake of a food with higher energy density and glycaemic index and lower dietary fibre, and higher consumption of fruits and vegetables,” the researchers explained. [Br J Nutr 2015;113(Suppl 2):S29-35]

Refined grains contain lower dietary fibre, vitamins and minerals, essential fatty acids, and phytochemicals due to the loss of the outer bran layer and the endosperm of the grain being pounded during the refining process. As a result, rapid action by digestive enzymes and quick absorption from the small intestines lead to an increase in postprandial blood glucose concentrations. [J Am Coll Nutr 2002;21:298-306; J Cereal Sci 2014;59:312-326]

The rise in glucose concentrations then elevates the insulin concentrations, resulting in hypoglycaemia, lipolysis, and the stimulation of hunger and food intake. [Int J Clin Exp Med 2017;10:12749-12755]