High refined carb intake tied to higher risk of death, heart issues

Increased consumption of refined grains* is associated with higher risk of mortality and major cardiovascular (CV) events, according to the large prospective PURE** study.

“[Our study from 21 countries***] has the distinct advantage of examining diets from diverse populations … covering broad patterns of diet globally,” said the researchers. With the increasing global rates of refined grain and added sugar intake, the findings suggest that reduced intake of refined grains should be considered, they stressed.

Using country-specific food frequency questionnaires (FFQs), data from 137,130 individuals without baseline CV disease (CVD) were analysed. After a median follow-up of 10 years, 10 percent (n=15,251) of participants had a composite^# of mortality or major CV events. About 40 percent of the 9,279 deaths were attributable to CVD. [BMJ 2021;doi:10.1136/bmj.m4948]

Compared with the lowest category of refined grain intake (<50 g/day), the highest category (≥350 g/day) correlated with a higher risk of total mortality (hazard ratio [HR], 1.28; p_trend=0.003), major CVD events (HR, 1.34; p_trend<0.001), and a composite of both outcomes (HR, 1.29; p_trend<0.001).

“Refined grains have lower dietary fibre content, vitamins and minerals, essential fatty acids, and phytochemicals, largely owing to the loss of the outer bran layer and the endosperm of the grain being pounded during the process of refining,” the researchers explained. The refined product in turn is digested uniformly and rapidly, thereby raising blood glucose concentrations. As a result, insulin concentration increases, leading to hypoglycaemia, lipolysis, and hunger stimulation, hence more food intake. [Int J Clin Exp Med 2017;10:12749-12755]

Whole grains, white rice: are they better carbs?

Conversely, no significant associations were observed between composite events and consumption of whole grains^## (HR, 1.05; p_trend=0.57 [50 to <100 g/day]) or white rice (HR, 0.96; p_trend=0.55 [≥450 g/day]) after full adjustments have been made including medications.

However, the effect with whole grains may have been driven by factors such as the varying definitions of whole grains, their distinct phytochemical structure, or agroclimatic factors. [J Agric Food Chem 2002;50:6182-6187; Am J Clin Nutr 2003;78:383-390; Nutr J 2013;12:62] Moreover, the effect of dietary carbohydrates on glycaemic response may vary by grain type and particle size. [Diabetes Care 1988;11:149-159] “This indicates that associations between whole grain intake and health outcomes are very complex and could be heterogeneous,” they further explained.

“[Also,] whole grains are often consumed with sugar, negating much of the benefit of whole grains. In our study … a variety of whole grains was consumed, and this may have obscured true associations with a specific form of whole grain,” they continued.

With rice, factors such as different varieties, cultivating and harvesting technologies, and cooking methods should be taken into context. [Br J Nutr 2015;114:1035-1045] Manner of consumption may have also influenced the results, as rice is mostly consumed with other dishes. [Public Health Nutr 2017;20:233-244]

“The composition of, and physiologic responses to, different kinds of rice vary … [As such,] caution must be exercised … so that high intakes of rice are not advocated indiscriminately without ensuring that total carbohydrate intakes are within the limits of the acceptable macronutrient distribution range,” they said.

The bottom line: choose your carbs

Despite potential confounders (eg, unaccounted sugar content in mixed foods, FFQs obtained at baseline only, diet changes), the diverse diet patterns offer wider generalizability of the findings. “We considered extensive covariates during analysis. [Adjusting for medications] did not change the results, indicating that our findings were robust,” said the researchers.

“[Taken together, cereal grains combined] with a lower intake of refined wheat products should be encouraged while promoting a higher intake of whole grains. Reduction in quantity and improvement in quality of carbohydrate is essential for better health outcomes,” they concluded.