Whole grains are a familiar part of heart-healthy eating advice, but how much do people actually need to eat to see a difference?
A new review of 87 randomized controlled trials suggests that higher whole grain intake may improve several measures tied to cardiovascular health. For many of those measures, the strongest overall pattern appeared around four to six servings a day. But the effects were generally modest, and the studies did not show that eating more whole grains directly prevents heart attacks or strokes.
The analysis, published in the European Heart Journal, included 6,529 adults from trials conducted in several parts of the world. Some participants were generally healthy, while others had conditions or risk factors such as type 2 diabetes, high cholesterol or excess weight.
“Although higher whole grain intake has long been linked to better heart health in population studies, clinical trials have produced mixed findings,” said lead researcher Helda Tutunchi of Tabriz University of Medical Sciences in Iran.
The researchers wanted to know whether looking across many trials together could provide a clearer picture, especially about how much whole grain might be needed to see benefits.
Overall, eating more whole grains was associated with small improvements in several areas, including LDL, or “bad,” cholesterol, total cholesterol, triglycerides, systolic blood pressure, body weight, waist size and fasting blood sugar.
The key word is small.
For example, every additional 48 grams of whole grains per day, which the researchers estimated at about three servings, was associated with an average drop of less than half a pound in body weight and less than 1 mmHg in systolic blood pressure. LDL cholesterol also fell modestly.
That means the study does not support the idea that simply adding whole grains to the diet will produce dramatic changes in weight, blood sugar or blood pressure.
Instead, the findings suggest that whole grains may help in several small ways at the same time.
The researchers found that many of the strongest changes showed up around 60 to 100 grams of whole grains per day by dry weight, or roughly four to six servings. Around that range, the clearest improvements were seen in cholesterol and systolic blood pressure.
But four to six servings should not be treated as a precise target for everyone.
The amount that appeared most helpful varied depending on what the researchers measured, and relatively few trials tested very high intakes. That makes it hard to say exactly where benefits level off. The authors described 60 to 100 grams per day as a useful benchmark, not a universal prescription.
What matters may also be what whole grains replace.
Some trials swapped whole grain foods for refined-grain versions, while others compared higher whole grain diets with people’s usual diets or with general dietary advice. Replacing white bread, refined cereal or white rice with whole grain alternatives may have a different effect than simply adding more food to the day.
That makes the findings less about piling on extra servings and more about choosing whole grains more often when grains are already part of the meal.
The studies included foods such as oats, brown rice, rye, whole wheat and other whole grains. To count as whole grain, the grain must retain the bran, germ and endosperm found in the original kernel.
The researchers were also careful about how much confidence to place in the findings. The evidence was rated stronger for some outcomes, including body weight, waist size and total cholesterol, and somewhat less certain for others. The trials also varied widely in the types of whole grains used, the people enrolled and what the whole grain diets were compared with.
Another limitation is that most trials were short. The typical study lasted about eight weeks, so it is unclear whether these small changes would continue, grow or disappear over the long term.
Most importantly, the researchers measured heart-health risk factors rather than actual cardiovascular events. Lower LDL cholesterol and blood pressure are generally linked with lower heart disease risk, but this review did not show that eating four to six servings of whole grains a day prevents heart attacks, strokes or cardiovascular deaths.
Still, the study helps explain why whole grains remain a regular part of healthy-eating recommendations.
As Tutunchi said, “Whole grains may benefit cardiovascular health through several modest improvements acting together, rather than through one large effect on a single risk factor.”
The meta-analysis was funded by Tabriz University of Medical Sciences in Iran.