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Eating more legumes can significantly lower blood pressure, blood glucose levels and risk for cardiovascular disease in patients with Type 2 diabetes, says new research led by the University of Toronto's David Jenkins.

“We know from our previous research that foods low on the glycemic index scale are helpful in lowering blood glucose levels,” said Jenkins, lead author of the study and professor in U of T’s Departments of Nutritional Sciences and Medicine. “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.”

Jenkins said focusing on the health impact of a specific, low-glycemic index food like legumes, which include beans, peas and lentils, “simplifies the take home message for patients.”

Jenkins, who is also the director of the Risk Factor Modification Centre at St. Michael’s Hospital, founded the glycemic index in the early 1980s. Health professionals use it to measure how much particular foods will raise blood sugar levels: those high on the index, such as white breads and sugary treats, cause a spike in blood sugar levels; those low on the index have a stable effect on blood sugar levels and include legumes, apples and berries.

The study, published online in the Archives of Internal Medicine, randomly assigned 121 patients with Type 2 diabetes to one of two groups. The control group ate a healthy, but not 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 that included at least one cup of legumes per day.

The participants’ blood pressure, body weight, blood glucose levels, blood fat and hemoglobin A1c (HbA1c) — a key indicator of diabetes control — were measured before and after the three-month study.

“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,” said Jenkins, who holds the Canada Research Chair in Nutrition and Metabolism.

“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.”