Research Stories

by Christine Lambrakis

Esther Martinez has eaten pinto beans most of her life, and she admits her family used to use lard when they prepared refried beans.

"Now, I eat pinto beans boiled with fresh tomato, whole onion and green chiles, or refry them with cheese in canola oil," Martinez says.

Little did she know that eating pinto beans, prepared without lard, may help lower her cholesterol level, even more so than eating the same serving size of a half cup of oatmeal, according to research conducted by ASU nutrition scientists.

When Martinez learned that her cholesterol was getting close to 200, though, and that she was pre-diabetic in 2005, she knew she had to do something to lose weight to address the threat of diabetes or heart disease before it was too late.

As an office specialist senior at ASU's Polytechnic campus, she saw the bean study as an opportunity to improve her health. Donna Winham, an ASU assistant professor of nutrition, was looking for subjects who met certain criteria, such as having higher cholesterol or being moderately insulin resistant (pre-diabetic), like Martinez.

"Beans are considered a very affordable, functional, healthy food rich in protein, complex carbohydrates, fiber, minerals and phytochemicals, which are non-nutritive plant chemicals that have protective or disease preventive properties," Winham says.

In 2005 and 2006, Winham and colleague Andrea Hutchins, with the University of Colorado-Colorado Springs, conducted their 24-week experiment to understand the impact of long-term legume consumption on biomarkers for heart disease and type 2 diabetes risks. In their research, they used canned pinto beans, and black-eyed peas and carrots as the placebo. The results of their efforts were published this past summer in the Journal of the American College of Nutrition.

"We chose these beans to study because they are common legume varieties consumed around the world as part of traditional diets," says Winham, whose research focuses on the use of traditional foods in reducing risk factors for heart disease and type 2 diabetes, and consumer beliefs and attitudes about bean consumption.

The 17 subjects who participated in the nine-month study were asked to eat a half-cup of pinto beans, black-eyed peas and carrots every day for eight weeks each.

"We found that daily pinto bean consumption of a half-cup resulted in an average drop of total cholesterol and LDL cholesterol of more than 8 percent," Winham says. "In contrast, a half-cup of oatmeal will reduce cholesterol 2 percent to 3 percent."

Initial results from the study suggested that pinto beans were effective at lowering overall cholesterol levels, and the black-eyed peas appeared to have little effect. However, closer analysis of the data showed that a few participants appeared to be less compliant in eating the black-eyed peas than the pinto beans or carrots. The researchers hope to retest black-eyed peas for cholesterol reduction.

"The benefit of the study is that it proves that long-term consumption of pinto beans does have a significant impact on lowering the risk of heart disease," Winham says. "A diet that incorporates beans might be as productive as taking a statin."

And while pinto beans have been proven to be effective, Winham and Hutchins stress that legume variety is key in the diet.

"Different beans are recognized for achieving different effects on biomarkers, so it's important to incorporate an assortment into the diet," Winham says.

The research was funded with a grant of $187,000 by Beans for Health Alliance (BHA) through the U.S. Agency for International Development (USAID). Her research is part of a larger project, conducted by the BHA, in which several studies are looking at these functional foods for health benefits.

All this research helps people like Martinez. Today, she continues to lose weight and incorporates beans into her diet almost on a daily basis.

"I'm not pre-diabetic anymore, and my overall cholesterol was at 186 after the study," Martinez proudly claims, and she did it without medications.

This article first appeared on the ASUNews web site.

For more information, contact Donna Winham by email at donna.winham@asu.edu