“Eat more whole grains” is one of the oldest pieces of nutrition advice around. What has been less clear is how much actually makes a difference. A new analysis in the European Heart Journal tries to put a number on it.
What the researchers did
A team led by Dr. Helda Tutunchi of Tabriz University of Medical Sciences in Iran combined the results of 87 randomized controlled trials involving 6,529 participants. The trials were run in Asia, Europe, the United States, Canada, Australia and Brazil, and each tested what happened when people ate more whole grains.
Randomized trials are the stronger kind of evidence because people are assigned to a diet rather than choosing it themselves. Population studies have long linked whole grains with better heart health, but trial results had been mixed. This review set out to answer a practical question: how much is enough?
What they found
Across the trials, eating more whole grains was linked to modest improvements in a whole list of heart risk factors:
- Lower body weight and smaller waist size
- Lower blood pressure
- Lower total cholesterol and LDL (“bad”) cholesterol
- Lower triglycerides and blood glucose
- Lower levels of interleukin-6, a marker of inflammation
The researchers rated the evidence as high certainty for body weight, waist size, total cholesterol and the inflammation marker, and moderate certainty for LDL cholesterol, triglycerides, systolic blood pressure, fasting glucose and insulin resistance.
What counts as a whole grain
In the editorial that accompanied the study, Dr. Cecilie Kyrø of the Danish Cancer Institute and colleagues explained that a whole grain keeps all three main parts of the kernel, the bran, the germ and the endosperm, in their original proportions. That can mean eating the grain whole, as rolled flakes, or ground into flour for bread and other foods. Refined grains lose much of the bran and germ, and with them much of the fiber.
They also noted that the idea isn’t new. More than half a century ago, researchers including Sir Denis Burkitt proposed that stripping fiber out of staple grains was behind a range of so-called Western diseases.
The “sweet spot”
Some benefits showed up at 30 to 40 grams of whole grains a day, measured as dry weight. The strongest effects, though, generally appeared at 60 to 100 grams a day, which the researchers equate to roughly four to six servings.
In everyday terms, the release describes that as something like a bowl of oatmeal, a sandwich on whole grain bread and a serving of brown rice over the course of a day.
An editorial published with the study noted that current US dietary guidelines recommend two to four servings of whole grains a day, and said the trial evidence suggests intakes toward the higher end, or above it, may be best for heart and metabolic health. Dr. Tutunchi was more cautious, saying the results don’t necessarily call for major changes to guidelines but do support helping people move toward the upper end of current targets.
Her team also made an interesting point about how whole grains seem to work. Rather than one dramatic effect, the benefit appears to come from several small improvements happening at once.
The catch
- The trials were short, about eight weeks on average, so it isn’t known whether the benefits last.
- The trials measured risk factors such as cholesterol and blood pressure, not actual heart attacks or strokes.
- Few trials tested very high intakes above 140 grams a day, so effects at that level are uncertain.
Putting it on the plate
The editorial’s advice was to replace refined grain foods with minimally processed whole grains, rather than reaching for highly processed products that simply have some whole grain added. A few easy swaps:
- A bowl of oatmeal at breakfast instead of a refined cereal
- Whole grain bread for your sandwich instead of white bread
- Brown rice in place of white rice at dinner
Spreading servings across the day, as in the study’s example, is an easier way to reach four to six than trying to fit them all into one meal.
If you have a condition such as celiac disease or a gluten intolerance, or you are managing blood sugar, it is worth checking with your doctor or a registered dietitian about which grains suit you.
This article is for general information, not medical advice.