Legumes are plants with seed pods that split into two halves. Edible seeds from plants in the legume family include beans, peas, lentils, soybeans and peanuts. Since peanuts are nutritionally similar to tree nuts, information on the health benefits of peanuts is presented in another article on nuts. Although legumes are an important part of traditional diets around the world, they are often neglected in typical Western diets. Legumes are inexpensive, nutrient-dense sources of plant protein that can be substituted for dietary animal protein (1). While sources of animal protein are often rich in saturated fats, the small quantities of fats in legumes are mostly unsaturated fats. Not only are legumes excellent sources of essential minerals, they are rich in dietary fiber and other phytochemicals that may affect health. Soybeans have attracted the most scientific interest, mainly because they are a unique source of phyotestrogens known as isoflavones (2). Although other legumes lack isoflavones, they also represent unique packages of nutrients and phytochemicals that may work synergistically to reduce chronic disease risk.
Note: Research on the health effects of diets rich in
legumes and soyfoods is summarized below. For a discussion of the potential
health benefits and risks of soy isoflavones, see the separate article
on Soy Isoflavones.
Dry Beans, Peas and Lentils
The glycemic index is a measure of the potential for carbohydrates in different foods to raise blood glucose levels. In general, consuming foods with high glycemic index values causes blood glucose levels to rise more rapidly, resulting in greater insulin secretion by the pancreas than consuming foods with low glycemic index values. Chronically elevated blood glucose levels and excessive insulin secretion are thought to play important roles in the development of type 2 diabetes mellitus (DM) (3). Because legumes generally have low glycemic index values, substituting legumes for high-glycemic index foods like white rice or potatoes lowers the glycemic load of one’s diet. Low-glycemic load diets have been associated with reduced risk of developing type 2 DM in several large prospective studies (4, 5). Obesity is another important risk factor for type 2 DM. Numerous clinical trials have shown that the consumption of low-glycemic index foods delays the return of hunger, decreases subsequent food intake, and increases the sensation of fullness compared to high-glycemic index foods (6). The results of several small short-term trials (1-4 months) suggest that low-glycemic load diets result in significantly more weight or fat loss than high-glycemic load diets (7-9). Thus, diets rich in legumes may decrease the risk of type 2 diabetes by improving blood glucose control, decreasing insulin secretion, and delaying the return of hunger after a meal. For more information on glycemic index values and glycemic load, see the article on Glycemic Index and Glycemic Load.
Dry beans, peas, and lentils
The only prospective cohort study to examine the effect of legume intake on cardiovascular disease risk found after 19 years of follow-up that men and women who ate dry beans, peas, or peanuts at least four times weekly had a risk of coronary heart disease (CHD) that was 21% lower than those who ate them less than once weekly (10). When compared to a typical Western diet, legume intake as part of a healthy dietary pattern that included higher intakes of vegetables, fruits, whole grains, fish, and poultry, was associated with a risk of CHD that was 30% lower in men (11) and 24% lower in women (12). The results of controlled clinical trials suggest that increasing dry bean consumption improves serum lipid and lipoprotein profiles. A meta-analysis that combined the results of 11 clinical trials found that increasing the consumption of dry beans resulted in modest (6-7%) decreases in total cholesterol and LDL-cholesterol (13). Several characteristics of dry beans may contribute to their cardioprotective effects. Dry beans are rich in soluble fiber, which is known to have a cholesterol-lowering effect. Elevated plasma homocysteine levels are associated with increased cardiovascular disease risk, and dry beans are good sources of folate, which helps to lower homocysteine levels. Dry beans are also good sources of magnesium and potassium, which may decrease cardiovascular disease risk by helping to lower blood pressure (13). The low glycemic index values of dry beans means that they are less likely to raise blood glucose and insulin levels, which may also decrease cardiovascular disease risk. For more information on glycemic index values, see the article on Glycemic Index and Glycemic Load.
Soy
In 1999, the US Food and Drug Administration (FDA) approved the following health claim: “Diets low in saturated fat and cholesterol that include 25 grams of soy protein a day may reduce the risk of heart disease (14).” Most of the evidence to support this health claim was included in a 1995 meta-analysis of 38 controlled clinical trials, which found that an average intake of 47 g/d of soy protein decreased serum total cholesterol levels by an average of 9% and LDL cholesterol levels by 13% (15). However, the results of clinical trials conducted since 1995 suggest that the LDL cholesterol-lowering effect of soy protein is more modest (16). Only 8 out of 22 controlled clinical trials conducted since 1998 found that supplementation with soy protein significantly lowered LDL cholesterol compared to milk or animal protein, and the overall reduction in LDL cholesterol was about 3% (17). A meta-analysis of 10 controlled clinical trials of soy protein conducted from 1995-2002 found a comparably modest overall reduction in serum LDL cholesterol (18). The consumption of isolated soy isoflavones (as supplements or extracts) does not appear to have favorable effects on serum lipid profiles (18-20). A recent science advisory from the Nutrition Committee of the American Heart Association concluded that earlier research indicating soy protein consumption resulted in clinically important reductions in LDL cholesterol compared to other proteins has not been confirmed (17). However, many soy products may be beneficial for overall cardiovascular health due to their relatively high content of polyunsaturated fat, fiber and phytosterols compared to animal products (21).
Dry beans, peas, and lentils
Although dry beans are rich in a number of compounds that could potentially reduce the risk of certain cancers, the results of epidemiological studies are too inconsistent to draw any firm conclusions regarding dry bean intake and cancer risk in general (22, 23).
Prostate cancer: There is limited evidence from observational studies that legume intake is inversely related to the risk of prostate cancer. In a 6-year prospective study of more than 14,000 Seventh Day Adventist men living in the US, those with the highest intakes of legumes (beans, lentils or split peas) had a significantly lower risk of prostate cancer (24). More recently, a prospective study of more than 58,000 men in the Netherlands found that those with the highest intakes of legumes had a risk of prostate cancer that was 29% lower than those with the lowest intakes (25). Similarly, in a case-control study of 1,619 North American men diagnosed with prostate cancer and 1,618 healthy men matched for age and ethnicity, those with the highest legume intakes had a risk of prostate cancer that was 38% lower than those with the lowest intakes (26). Excluding the intake of soy foods from the analysis did not weaken the inverse association between legume intake and prostate cancer, suggesting that soy was not the only legume that conferred protection against prostate cancer.
Soy
Prostate cancer: Although there is considerable scientific interest in the potential for soy products to prevent prostate cancer, evidence that higher intakes of soy foods can reduce the risk of prostate cancer in humans is limited. Only two out of six case-control studies found that higher intakes of soy products were associated with significantly lower prostate cancer risk. In the largest case-control study, North American men who consumed an average of at least 1.4 oz of soy foods daily were 38% less likely to have prostate cancer than men who did not consume soy foods (26). A much smaller case-control study of Chinese men found that men who consumed at least 4 oz of soy foods daily were only half as likely to have prostate cancer as those who consumed less than 1 oz daily (27). However, case-control studies conducted among North American (28,29), Japanese (30), and Taiwanese men (31) did not find that higher soy intakes were associated with significantly lower prostate cancer risk. A 6-year prospective cohort study of more than 12,000 Seventh Day Adventist men in the US found that those who drank soy milk more than once daily had a risk of prostate cancer that was 70% lower than those who never drank soy milk (32), but a 23-year study of more than 5000 Japanese American men found no association between tofu consumption and prostate cancer risk (33).
Breast cancer: At least 15 epidemiological studies have assessed the relationship between soy food intake and the risk of breast cancer. Only one out of four prospective studies (three in Asian populations and one in a US population) found that higher intakes of a soy food were associated with a significant reduction in breast cancer risk. In that 9-year study of more than 21,000 Japanese women, higher intakes of miso soup, but not other soy foods, were inversely associated with breast cancer risk (34). Most case-control studies did not find that women with higher soy intakes were at lower risk of breast cancer, except for women who had higher soy intakes during adolescence (35,36). Two case-control studies, one of Chinese women (37) and one of Asian-American women (38) found that women with higher soy intakes during adolescence were significantly less likely to develop breast cancer later in life.
Substituting beans, peas and lentils for foods that are high in saturated fat or refined carbohydrates is likely to help lower the risk of type 2 DM and cardiovascular disease. Soybeans and foods made from soybeans (soy foods) are excellent sources of protein. In fact, soy protein is complete protein, meaning it provides all of the essential amino acids in adequate amounts for human health (2). Like beans, peas and lentils, soy foods are also excellent substitutes for protein sources that are high in saturated fat like red meat or cheese. Although a number of health-related organizations recommend daily consumption of 5-9 servings (2 ½-4 ½ cups) of fruits and vegetables daily (see Fruits and Vegetables), few make specific recommendations for legumes. In the 2005 Dietary Guidelines for Americans, an intake of 3 cups (6 servings) of legumes weekly is recommended for people who consume about 2000 kcal/d. A serving of legumes is equal to ½ cup of cooked beans, peas, lentils or tofu (39).
Macronutrients |
Vitamins |
Minerals |
Phytochemicals |
| Essential Fatty Acids | Folate | Magnesium | Fiber |
| Potassium | Flavonoids | ||
| Soy Isoflavones | |||
| Lignans | |||
| Phytosterols | |||
Written by:
Jane Higdon, Ph.D.
Linus Pauling Institute
Oregon State University
Reviewed by:
James W. Anderson, M.D.
Professor of Medicine and Clinical Nutrition
University of Kentucky School of Medicine
Last updated 12/19/05 Copyright 2004-2008 Linus Pauling Institute
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The Linus Pauling Institute Micronutrient Information Center provides scientific information on health aspects of micronutrients and phytochemicals for the general public. The information is made available with the understanding that the author and publisher are not providing medical, psychological, or nutritional counseling services on this site. The information should not be used in place of a consultation with a competent health care or nutrition professional.
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