(Reuters Health) - Scientists haven’t yet proved beyond a doubt that a diet rich in whole grains is healthy for the heart, a research review suggests.
Researchers focused only on the gold standard for nutrition experiments: studies that randomly selected some healthy adults to consume lots of whole grains from products like cereal, rice and oats - and other healthy individuals to eat plenty of refined grains like white bread or stick to their usual diets.
None of these experiments tested whether eating whole grains might influence the risk of dying from heart disease or having a heart attack or stroke, the research review found.
All of the experiments did assess how consuming whole grains impacts risk factors for heart disease like blood pressure and cholesterol, however, and none found a difference in these risk factors based on what types of grains people ate.
But there is still a large and undisputed body of evidence documenting the many health benefits of a diet rich in whole grains, said Nour Makarem, a nutrition researcher at Columbia University in New York who wasn’t involved in the study.
“Whole grains have been associated with lower weight gain, better cholesterol, glucose and insulin levels in previous studies, which are risk factors for heart disease,” Makarem said by email.
“Whole grains are also a source of cereal fiber, which has in turn been associated with lower risk for heart disease, obesity and cancer,” Makarem added.
The American Heart Association recommends the Dietary Approaches to Stop Hypertension (DASH) diet or a Mediterranean-style diet to help prevent cardiovascular disease. Both diets emphasize cooking with vegetable oils with unsaturated fats, eating nuts, fruits, vegetables, low-fat dairy products, whole grains, fish and poultry, and limiting red meat and added sugars and salt.
In the current research review published by the Cochrane Library, the authors conclude that experiments to date testing the heart benefits of whole grains have been too small, too brief, or both, making it impossible to determine how these foods might lead to long-term heart benefits in the general population.
Combined, the nine studies included in the review had only 1,414 participants ranging in age from 24 to 70. None of the studies tested the impact of consuming whole grains for longer than four months.
Senior study author Dr. Karen Rees of the University of Warwick in the UK didn’t respond to requests for comment.
Whole grain foods encompass a range of products and include whole grain wheat, rice, maize, and oats as well as milled whole grains such as oatmeal.
High-fiber grains are only one component of a healthy diet, noted Dr. Margo Denke of Bandera, Texas, a former researcher at the University of Texas Southwestern Medical Center in Dallas who wasn’t involved in the current research review.
“We have known for some time that fiber makes a small contribution to altering risk factors for heart disease,” Denke said by email.
“The point is that whole grains, when added to a whole diet of fruits and vegetables (as seen with the DASH diet) do make a difference in cardiovascular risk factors,” Denke said. “One needs to quit asking small modifications to bear the weight of the effects of a complete diet; diet is not a simple thing and diet is a composite, an overall approach to life.”
SOURCE: bit.ly/2xbO3jC Cochrane Database of Systematic Reviews, online August 24, 2017.