How Do Beans Reduce Risk of CVD?
By Maureen A. Murtaugh, Ph.D., RD
Legumes, including dried beans and nuts, are a rich source of many nutrients including vegetable protein, minerals, including calcium, zinc, iron, and selenium and soluble fiber. Beans are inexpensive protein sources as demonstrated by the Special Supplemental Nutrition Program for Women, Infants, and Children. Importantly, pinto beans, black beans, and other dry beans are traditional components of diets for cultural groups widely represented in the United States. Therefore, their acceptability may be more widespread than that of soybeans and soy products.
There are several mechanisms through which consumption of beans may reduce risk of cardiovascular disease. Their composition is sufficiently different from soy and nuts to consider a synergy of beans, soy or walnuts in reducing risk of CVD (Table 1). Components including soluble fiber, phytochemicals, vegetable protein, calcium, and selenium have the potential to alter risk factors for cardiovascular disease including hypercholesterolemia, blood pressure, body weight, and oxidative status.
Hypocholesterolemic Effect
Incorporation of beans into the diet may help to optimize lipid profile, although the exact mechanism of action is unknown. It has long been known that soluble fiber is hypocholesterolemic.(2) In 1984 a parallel clinical trial using almost 2 cups of dry beans vs. about 1¼ cup of oatbran daily (to provide similar soluble fiber) over 3 weeks resulted in reduced total cholesterol and LDL cholesterol. The reductions were similar for the oatbran (-19% total cholesterol and -23% LDL) and bean diets (-19% total cholesterol and -24% LDL cholesterol). However, the study suggested that the mechanisms for the reduction were distinct. While oatbran consumption increased fecal bile acid excretion, beans did not, suggesting a different mechanism for the reduction in total and LDL cholesterol. Since then, other intervention studies with beans also demonstrated a reduction in total cholesterol, LDL, VLDL, and triglyceride levels.(3-6)
Lower Blood Pressure
Increased intake of magnesium, fiber, and potassium among bean eaters may help to promote optimal blood pressure levels. Investigators using the NHANES data from 1999-2002 identified a 47% reduction in risk of elevated systolic blood pressure among bean eaters between the ages of 20 and 40 as compared to non-bean eaters.(7) Although this evidence is cross-sectional, it does suggest a role of bean consumption in maintenance of healthy blood pressure.
Lower Body Weight
A prolonged postprandial presence of food in the intestine with consumption of beans (8) and reported greater satiety after consumption of a bean puree as compared to a potato puree (9) may contribute to lower weight. Slightly lower body weight with the addition of beans to the diet despite constant energy intake has been reported from a clinical trial. (4) More frequent bean consumption is associated with lower BMI among NHANES participants.(10)
Oxidation
Using a variety of beans including those rich in color such as red kidney beans, pinto beans and black beans is one strategy to increase antioxidant content of diet. Phenol antioxidants (11) contribute to the significant antioxidant activity present in dry beans.(12) The antioxidant activity of red kidney beans and pinto beans may contribute to reduced LDL oxidation and contribute to decreased risk of a heart attack and other cardiovascular disease outcomes through this mechanism.
How much is enough, but not too much?
Evidence suggests that as little as 1/3 to ½ cup of dry beans per day or perhaps even just four times per week is enough to observe decrease in cardiovascular risk, weight, and lipid profile. Of the available adult cohort studies, one indicated consumption of 4 servings of beans per week was associated with an 11% reduction in risk of cardiovascular disease and an 11% reduction in coronary heart disease outcomes as well as lower body weight.(10) In Central America, one serving (1/3 cup cooked beans per day) was associated with a 38% lower risk of a heart attack, with no further increase when intake was greater than 1 serving per day. A randomized cross-over study using ½ cup pinto bean consumption daily for 8 weeks had a reduction in total cholesterol of 19% ±5, and a reduction in LDL cholesterol of 14% ± 4. (3)
Practical aspects of increasing beans in the diet
Common barriers to increasing beans in the diet include an increase in gas or bloating. Dietitians might recommend that a client add small amounts, such as ¼ to ½ cup every few days. Clients should be consuming adequate fluids throughout the day and with the meal. A gradual increase in frequency of eating beans to ½ cup nearly every day can help to reduce side effects. Over-the-counter products (Beano® or Bean-zyme) are available to help clients reduce gas, when not contraindicated by galactosemia or allergy.
There are several strategies that can be used to increase consumption of beans. Beans can be incorporated into many mixed dishes such as casseroles and stews, used in dips to be eaten with vegetables as a snack, or substituted for garbanzo beans in hummus. Beans are an excellent addition to vegan, vegetarian, or even meat containing soups. Adding ½ cup beans to a salad increases protein and fiber and may increase satiety as well.
Table One Caption: Nutrients per one cup cooked dry beans, soybeans, and walnuts.
About the author: Dr. Murtaugh pursued her PhD in Nutrition Sciences from the University of Connecticut. She was on the faculty at Rush University for eight years before completing a post-doctorate in epidemiology at the University of Minnesota. She is associate professor at the University of Utah investigating nutrition in development of chronic disease management.
References
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