Downing a cup of beans or lentils every day may help people with type 2 diabetes control their blood sugar and possibly reduce their risk of heart attacks and stroke, according to a small study out Monday.
Researchers found that compared with a diet rich in whole grains, getting a daily dose of legumes led to small drops in an important measure of blood sugar as well as in blood pressure and cholesterol levels.
After three months on the bean diet, study participants' estimated 10-year risk of cardiovascular disease had fallen from 10.7 percent to 9.6 percent, according to findings in the Archives of Internal Medicine.
"Legumes are good protein sources, and proteins tend to dampen the blood glucose response and they lower blood pressure," said Dr. David Jenkins of St. Michael's Hospital in Toronto, who led the work.
"They are also good sources of fiber and that tends to be associated with lower cholesterol," he told Reuters Health.
Jenkins said that even though the drops were not huge, they were impressive in part because the whole-grain comparison diet is a healthy one and in part because people in the study were already on diabetes and blood pressure drugs.
"We hope that this could be the point that allows you to delay medication use," Jenkins said. But, he added, "if we can keep people on medications throughout their life and not have complications of diabetes, we have won."
Legumes such as beans, chickpeas and lentils are already recommended for diabetics due to their low glycemic index, a measure of how far and how fast a given food sends up blood sugar. But there are few studies of their direct effects in diabetes, according to Jenkins and his colleagues.
They divided 121 people with diabetes into two groups, one of which was instructed to up their intake of cooked legumes by at least a cup a day. The other was told to eat more whole wheat products to boost their fiber intake.
After three months, the researchers found that hemoglobin A1c levels had dropped from 7.4 percent to 6.9 percent in people eating beans, while it had fallen from 7.2 percent to 6.9 percent in those getting extra whole wheat.
The number reflects the average blood sugar levels over the past two to three months and experts recommend keeping it under seven percent.
"We were able to drop them into the 6s where you want them," said Jenkins. He added that U.S. health regulators consider a change of 0.3 or 0.4 percentage points to be "therapeutically relevant."
The larger reduction seen with legumes as opposed to whole wheat - 0.2 percentage points - was statistically reliable, but it is unclear exactly what it means for diabetics.
There was no reduction in blood pressure with extra whole wheat, but a drop from 122 to 118 points in systolic blood pressure (the top number) with legumes and from 72 to 69 in diastolic (the bottom number). Blood pressure readings are considered normal if they are no more 120 over 80.
Given the lower blood pressure, Jenkins and his colleagues calculated that diabetics getting a daily dose of beans would lower their 10-year risk of heart attack or stroke by just under one percentage point compared with people eating whole wheat.
By comparison, cholesterol-lowering drugs are thought to cut 10-year cardiovascular risk by about 20 percent - or two percentage points in people with a baseline risk of 10 percent.
The study didn't find any more gastrointestinal complaints in the legume group, apparently deflating the notion that downing lots of beans leads to excessive flatulence. Jenkins did warn, however, that the comparison group also got a lot of fiber, which could have drowned out a potential effect.
He said people across the globe have recently shifted away from eating legumes.
"The public should be doing some preventive strategies using these foods," he said. "We are not introducing some novel "Frankenfood" into the diet - this is really deep, traditional stuff."
An editorial published with the study notes that nutrition therapy is effective in diabetes, but questioned whether people with the disorder can eat enough legumes to reap the benefits.
Marion Franz of Nutrition Concepts by Franz Inc in Minneapolis, who wrote the editorial, also said it's unclear whether the potential effect of legumes is related to their low glycemic index or their high fiber content.