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High Intake of Refined Grain Increases Heart Disease Risk, Study Shows

Load of sliced white bread on chopping board

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Key Takeaways

  • Most dietary plans recommend whole grains over refined grains, because they contain more nutrients.
  • A recent study of 21 countries found that people who eat the most refined grains have a higher risk of total mortality and major cardiovascular events.
  • No significant associations were found between whole grains or white rice with cardiovascular outcomes.

Globally, many nutrition guidelines recommend choosing whole grains over refined grains, and a new study published in the British Medical Journal may help explain part of the reason why. Researchers have linked high intake of refined grains with an increased risk of heart disease.??

Why Grain Type Matters

Whole grains, such as brown rice, oats, and whole wheat, are often linked to lower blood pressure and better cholesterol levels, and are protective of cardiovascular health.??

“Whole grains have all components of the grain intact, which means they have more fiber and vitamins, and have a lower glycemic index than refined grains,” explains Dr. Mahshid Dehghan, principal investigator at the Population Health Research Institute at McMaster University in Hamilton, Ontario.

Glycemic index is a very simple measure of how food increases blood glucose,” says Dehghan. “The glycemic index of refined grains is high and they increase blood glucose very fast."

This is important since past meta-analyses have linked a high dietary glycemic load with a higher risk of heart disease and stroke.??

Dehghan explains that whole grains gradually increase blood glucose, which is one reason why they are healthier than refined grains.

Refining a grain involves removing the outer layer of the grain, which results in less fiber, vitamins, minerals, and fatty acids, compared to whole grains.

Researchers have been studying the impact of whole vs. refined grains on blood sugar, Type 2 diabetes, and heart health for many years, and have noted that higher intakes of dietary fiber from whole grains can protect against cardiovascular disease and Type 2 diabetes.??

A past meta-analysis found that whole grain intake was associated with a reduced risk of coronary heart disease and cardiovascular diseases, specifically with an intake of about seven servings of whole grains daily (about 210-225 g/day).??

The same study found little evidence of an association of heart health benefits with refined grains or white rice.

Another meta-analysis found inverse relationships between whole-grain intake and mortality due to cardiovascular disease, which lead them to recommend increasing whole grain consumption.?

Many studies have shown the association between whole grain consumption and lower CVD risk. Less is known about refined grains and white rice on CVD outcomes. 

The Latest Study

In the new study published in the British Medical Journal, Dehghan and a team of investigators from around the world looked for patterns between grains and heart disease, blood pressure, and mortality.

This large prospective cohort study included 137,130 people in the Prospective Urban and Rural Epidemiology (PURE) study, with a median follow-up of 9.5 years.

The study population is unique because it includes people from 21 low-, middle-, and high-income countries throughout North America, Europe, South America, Africa, and Asia.

Dietary information was obtained using a food frequency questionnaire one time at the beginning of the study. Questionnaires used country-specific foods and eating patterns.

Grains were looked at in the following three categories:

  1. Refined grains: low-fiber white flour, plus foods made with flour, including bread, noodles, cereals, and desserts
  2. Whole grains: unprocessed wheat, rye, oats, barley, maize, millet, sorghum, corn, and buckwheat
  3. White rice: long- and short-grain varieties

Dr. Mahshid Dehghan

Whole grains have all components of the grain intact, which means they have more fiber and vitamins, and have a lower glycemic index than refined grains.

What Did the Study Find?

Upon analysis of dietary habits and health over the study time period, the researchers found that:

  • China had the highest intake of refined grains, compared to any other region.
  • The intake of white rice was highest in South Asia, including India.
  • The intake of whole grains was highest in Africa.
  • People who ate the highest amount of refined grains (more than 350 g/day) had a higher risk of total mortality, major cardiovascular events, and stroke, compared to people who ate less than 50g day of refined grains.
  • The association of refined grains with cardiovascular outcomes was apparent in China, but not in other regions.
  • Eating more refined grains was associated with higher blood pressure.
  • No significant associations were found between whole grains or white rice with cardiovascular outcomes.
  • Including sodium or saturated fat into the models didn’t change the results.

Please note that this study shows associations only, and was not designed to show cause and effect. This study is an interesting way to examine patterns, but it alone should not dictate your personal eating habits.

Why Do Refined Grains Make a Difference?

When grains are stripped of their bran layer in the refining process, they lose fiber, vitamins, minerals, and essential fatty acids.

A consequence of the refining process is that refined grains are quickly broken down by digestive enzymes, which leads to a quick absorption from the small intestines and a rise in post-meal blood sugar levels. This has been linked with Type 2 diabetes and poor heart health.

This study does a good job of emphasizing that the amount of whole vs. refined grains makes a difference to health. The adverse results on heart health were seen with about 350 grams a day of refined grains, but not at lower levels.

Dehghan explains that, at this high level, refined grains may be replacing more nutritious foods in the diet, which may increase heart disease risk.

What About White Rice?

By definition, white rice has the outer bran layer removed, which makes it a refined grain. But in this study, it’s in a separate category than the refined grains. Why is that?

White rice was separated from the other refined grains because more than 60% of the PURE population reside throughout Asia, where rice is a staple food.

Dehghan explained that prior studies?? also showed no association between rice consumption and CVD, but she emphasizes again that quantity matters—this study showed no impact on heat health at intake levels below 350 g/day.

“We also don’t have one type of rice,” says Dehghan. “We have parboiled, short, long, basmati, and they have different glycemic indices and different cooking methods.”

She says that in South Asia and the Middle East, people soak rice overnight, then boil, drain and cook again.

“When you do that, you decrease the amount of starch and change the glycemic index, as well, meaning not all rice breaks down the same way,” says Dehghan. “Also, the rice grain is mostly intact, therefore accessibility for enzymes is less than when you look at milled refined grains.”

Cooking and reheating white rice also can reduce its glycemic index.??

Breanna Woods, RD

I always encourage choosing whole grains over refined grains as often as possible.

— Breanna Woods, RD

What About Sugar?

Sugar in pastries and baked goods was included in the refined grains category. Verywell asked Dehghan to explain why.

“The refined grain group did include sweets such as cake and pastries,” says Dehghan. “The harm to cardiovascular health comes from both sugar and flour.”

She explained that when the researchers examined foods with different ingredients, such as a cake with egg, sugar, flour, and oil, they proportionally weighed each ingredient and accounted only for the ingredients they were interested in.

“We’re not as much concerned with sugar from sweets and desserts in this study, because in low-income countries, sugar consumption is very low," she says.

Interestingly, Dehghan’s next analysis is on sugar and sweets in ultra-processed foods, and will look more closely at sugar, in general. So, more to come on the topic of sugar’s impact on heart health.

Which Grains Should You Choose?

Verywell reached out to Breanna Woods, a dietitian in Indianapolis, Indiana, for some advice.

“I always encourage choosing whole grains over refined grains as often as possible,” says Woods.

“For clients who eat a diet heavy in refined grains, I recommend starting with a goal to make 50% of the grains they eat whole grains," says Woods. "Then I work with them to increase that amount from there.”

And what about white rice? Woods explains to her clients that white rice lacks fiber and other nutrients, but ultimately, she leaves it up to preference.

“As this study shows, the benefit of choosing white rice over brown rice is minimal as far as overall health is concerned,” says Woods.

What This Means For You

When possible, swap out refined grains for whole grain options. Try oats, hulled barley, whole grain wheat, or rye instead of the usual white bread and refined breakfast cereals. If you enjoy white rice, do so in moderation, which means no more than 350 grams per day.

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