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A cup of beans a day has health benefits, new research shows

Toronto, October 22, 2012

By Kate Taylor

Dr. David Jenkins
Dr. David Jenkins

Eating more legumes such as beans, peas and lentils can significantly lower blood pressure, blood glucose levels and risk for cardiovascular disease in patients with Type 2 diabetes according to new research from St. Michael's Hospital.

"We know from our previous research that foods low on the glycemic index scale are helpful in lowering blood glucose levels," said Dr. David Jenkins, lead author of the study and director of the hospital's Risk Factor Modification Centre. "But this is the first study of its kind to specially look at legumes' effect on cardiovascular risk factors and find they also have a blood pressure lowering effect in diabetic patients."

Dr. Jenkins said that focusing on the health impact of a specific food like legumes - among the lowest glycemic index foods - rather than the glycemic index as a whole, "simplifies the take home message for patients."

The glycemic index was founded by Dr. Jenkins and is used to measure the extent to which a particular food will raise blood sugar levels. Foods high on the glycemic index scale are ones that cause a spike in blood sugar levels such as white breads and sugary treats. Those low on the index have a stable effect on blood sugar levels and include foods like legumes, apples and berries.

The study, which appeared online in the Archives of Internal Medicine today, randomly assigned 121 patients with Type 2 diabetes to one of two groups. The control group ate a healthy but not a low glycemic index diet that included more insoluble fibre in the form of whole wheat grains. The test group was given a low-glycemic index diet specifying eating at least one cup of legumes per day.

The participants' blood pressure, body weight, blood glucose levels, blood fat and hemoglobin A1c (HbA1c) - the "gold standard" for diabetes control - were measured before and after the three month study.

The results showed a beneficial effect on all measurements except blood pressure for the control group, whereas the test group had a beneficial effect on all measurements as well as a significant reduction in HbA1c values and risk for coronary heart disease, both driven by a reduction in blood pressure.

"Legume consumption of approximately one cup per day seems to contribute usefully to a reduction in blood pressure which is hugely important for diabetic patients," Dr. Jenkins said. "High blood pressure is a big contributor to renal failure in these patients, and so if you can control both their blood pressure and glucose levels together, you have a very powerful treatment advantage."

Dr. Jenkins also has appointments with the University of Toronto's Departments of Medicine and Nutritional Sciences. He also serves as Canada Research Chair in Nutrition and Metabolism. In a separate paper, Dr. Jenkins' colleague Arash Mirrahimi, a research assistant at the Risk Factor Modification Centre, found that people who ate foods high on the glycemic index scale were up to 14 per cent more likely to be at risk for an acute heart attack or death due to coronary heart disease than those who ate foods low on the index.

Mirrahimi and colleagues reviewed and pooled results from 12 studies that looked at the risk of having coronary heart disease based on the types of diets participants were eating.

They found that women who ate higher glycemic index diets were particularly susceptible and had a 26 per cent higher risk for coronary heart disease than women with lower glycemic index diets.

The paper appeared this month in Journal of the American Heart Association.

"Heart disease is the leading cause of death worldwide," Mirrahimi said. "Our findings show the importance of lifestyle in modifying the risk for this disease."

About St. Michael’s Hospital

St. Michael’s Hospital provides compassionate care to all who enter its doors. The hospital also provides outstanding medical education to future health care professionals in more than 23 academic disciplines. Critical care and trauma, heart disease, neurosurgery, diabetes, cancer care, and care of the homeless are among the Hospital’s recognized areas of expertise. Through the Keenan Research Centre and the Li Ka Shing International Healthcare Education Center, which make up the Li Ka Shing Knowledge Institute, research and education at St. Michael’s Hospital are recognized and make an impact around the world. Founded in 1892, the hospital is fully affiliated with the University of Toronto.