Oct. 22, 2012 -- Adding beans and other legumes to the diet appears to help people with type 2 diabetes improve their blood sugar control and lower their risk of heart disease, according to new research.
Two diets were tested in 121 men and women with type 2 diabetes. Both diets were healthy, but one added legumes, such as chickpeas, lentils, and beans.
"People with diabetes did better in terms of blood sugar control on the bean diet versus a diet without beans, which was otherwise extremely healthy," says researcher David J.A. Jenkins, MD, PhD, DSc, professor of medicine and nutrition at the University of Toronto and St. Michael's Hospital in Toronto.
The bean diet lowered the predicted risk of heart disease more, too, Jenkins says. And it did so in a way that surprised him, he says. "It reduced heart disease risk predominantly because of its effect on blood pressure," he says.
While Jenkins is a backer of the bean diet, a nutrition expert who wrote a commentary published with the study questions if the beans deserve the credit, or the high fiber in the bean-heavy diet.
The study and commentary are published online in the Archives of Internal Medicine.
The study was funded by Canada's federally funded ABIP (Agricultural Bioproducts Innovation Program) through the Saskatchewan Pulse Growers (legumes) and PURENet (Pulse Research Network).
Bean Diet Study Details
Legumes are known as low glycemic index foods. The index measures the effects of sugar in food on blood sugar. Jenkins says legumes have been shown to improve blood sugar control in people with type 2 diabetes.
Jenkins assigned half the men and women to follow a healthy diet high in wheat fiber. They ate whole grain cereals, low-fat dairy, and fruits and vegetables, he says. The other half was told to eat a healthy diet, including a cup of legumes per day, or about two servings.
Each group got a checklist of recommended foods and quantities to eat every day.
The study lasted three months.
Beans and Blood Sugar: Results
The bean diet improved blood sugar control more, as measured by the HbA1C test.
This lab test provides a measure of average blood sugar control over the previous two to three months.
People with diabetes are advised to aim for a level of below 7%.
The values declined by .5% in those on the bean diet and .3% in those on the high wheat fiber diet.
Reductions of .3% to .4% are considered meaningful by the FDA, Jenkins writes.
The average for both groups at the study end was 6.9%. However, those in the high wheat fiber diet group started at 7.2%. Those in the bean diet group started at 7.4%.
Beans and Heart Risk: Results
Next, Jenkins calculated their predicted risk of heart disease. He used a standard equation that plugs in blood pressure and other health measures.
Those on the bean diet had a greater risk reduction in the heart disease prediction than those on the high wheat fiber diet.
How it reduced the heart disease risk score was a surprise to Jenkins. "It reduced heart disease risk predominantly because of its effect on blood pressure," he says. "That came as a shock to us."
Those on the bean diet started with an average blood pressure of 122/72 and ended with 118/69. (Below 120/80 is normal.) That difference looks slight, Jenkins says, but is considered significant.
Those on the high wheat fiber diet started out with blood pressures averaging 118/70 and had the same average at the end of the study.
Jenkins' advice? "Swap a few of your meat meals for bean stew," he says. Lentil soup or bean chili are among other options.
Symptoms such as bloating or gas were about the same in both groups, he says.
Jenkins reports serving on the scientific advisory boards of numerous companies and organizations, including the Saskatchewan Pulse Growers and Agri-Culture and Agri-Food Canada.
Bean Diet: Another Perspective
"Beans are part of a healthful eating pattern," says Marion Franz, RD, a nutrition consultant in Minneapolis. She wrote an invited commentary to accompany the study.
However, she wonders how long most people can keep up a cup-a-day bean habit.
She also questions if the beans by themselves deserve all the credit. "The group that ate the low glycemic index diet also ate considerably more fiber," she says.
The bean group started out eating 15.6 grams of fiber a day. At the end of the study, they averaged 25.6 grams.
The high wheat fiber group started out with 16.6 grams a day and ended at 18.5 grams.
A cup of navy beans, for instance, has about 19 grams of fiber.