Highlights
Protein and fiber rich legumes including peas, beans and lentils are known to have many health benefits including reduced risk of heart diseases, diabetes, cholesterol and constipation and improved blood pressure. Different population-based (cohort) studies also indicated that food/diet rich in legumes such as peas, beans and lentils may be associated with a reduced risk of specific cancer types such as breast, colorectal and prostate cancers. However, higher intake of legumes may not reduce the risk of endometrial cancer.
What are Legumes?
Leguminous plants belong to the pea family or Fabaceae family of plants. The root nodules of these plants host the rhizobium bacteria and these bacteria in turn fix nitrogen from the atmosphere into the soil, which are used by the plants for their growth, thereby forming a symbiotic relationship. Hence, leguminous plants are popular for their nutritional as well as environmental benefits.
Leguminous plants have pods with seeds inside them, which are also known as legumes. When used as dry grains, these seeds are called pulses.
Some of the edible legumes include peas; common beans; lentils; chickpeas; soybeans; peanuts; different types of dry beans including kidney, pinto, navy, azuki, mung, black gram, scarlet runner, ricebean, moth, and tepary beans; different types of dry broad beans including horse and field beans, dry peas, black-eyed peas, pigeon peas, bambara groundnut, vetch, lupins; and others such as winged, velvet and yam beans. The nutritional quality, appearance and taste may vary across different types of pulses.
Health Benefits of Legumes
Pulses are extremely nutritious. Legumes such as peas, beans and lentils are an excellent source of proteins and dietary fibers and are known to have different health benefits. Pea proteins are taken as food or supplements and are extracted in powder form from the yellow and green split peas.
Apart from proteins and dietary fibers, legumes are also packed with a variety of other nutrients including :
- Antioxidants
- Minerals such as iron, magnesium, zinc, calcium, potassium
- B vitamins such as folate, vitamin B6, thiamine
- Carbohydrates including resistant starch
- Dietary plant sterols such as β-sitosterol
- Phytoestrogens (plant compounds with estrogen like property) such as Coumestrol
Unlike foods such as red meat, pulses are not high in saturated fats. Due to these benefits, protein rich legumes including peas, beans and lentils are considered to be an excellent alternative healthy food to red meats and are also used as a staple food in many countries across the world. Additionally, these are also inexpensive and sustainable.
Eating pulses including peas as part of a healthy diet and lifestyle may be associated with a variety of health benefits which include:
- Preventing constipation
- Reducing the risk of heart disease
- Lowering cholesterol levels
- Improving blood pressure
- Preventing type 2 diabetes
- Promoting weight loss
However, along with these health benefits, there are some known drawbacks for these low-fat, high protein peas, beans and lentils as they contain certain compounds known as anti-nutrients. These may reduce our body’s ability to absorb certain nutrients.
Examples of these anti-nutrients which can reduce the absorption of one or more of the nutrients including iron, zinc, calcium and magnesium are phytic acid, lectins, tannins and saponins. Uncooked legumes contain lectins which can cause bloating, however, if cooked, these lectins present on the surface of the legumes can be removed.
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Legume Intake and Risk of Cancer
Being a nutritious food with varied health benefits, researchers across the world have been interested in understanding the association between intake of these protein and dietary fiber rich legumes including peas, beans and lentils and the risk of cancer. Different population based studies and meta-analyses have been carried out to evaluate this association. Various studies have also been carried out to investigate the association of specific nutrients present in high amounts in leguminous foods such as peas, beans and lentils with the risk of different cancer types.
Some of these studies and meta-analyses are collated in the blog.
Legume Intake and Breast Cancer Risk
Study on Iranian Women
In a very recent study published in June 2020, the researchers evaluated the association between legume and nuts intake and breast cancer risk in Iranian women. For the analysis, data based on a 168-item semi-quantitative food frequency questionnaire was obtained from a population-based case-control study which included 350 breast cancer patients and 700 controls whose age and socioeconomic status were matched with that of the breast cancer patients. Legumes considered for the study included protein rich lentils, peas, chickpeas, and different kinds of beans, including red beans and pinto beans. (Yaser Sharif et al, Nutr Cancer., 2020)
The analysis found that among postmenopausal women and normal-weight participants, groups with a high legume intake had a 46% lower risk of breast cancer compared with those with low legume intake.
The study concluded that an increased consumption of protein and dietary fiber rich legumes such as peas, chickpeas and different types of beans may benefits us in reducing the risk of breast cancer.
San Francisco Bay Area Breast Cancer Study
A study published in 2018 evaluated the association between legume/bean intake and breast cancer subtypes based on the status of estrogen receptor (ER) and progesterone receptor (PR). The food frequency data for the analysis was obtained from the population-based case-control study, named the San Francisco Bay Area Breast Cancer Study, which included 2135 breast cancer cases consisting of 1070 Hispanics, 493 African Americans, and 572 non-Hispanic Whites; and 2571 controls consisting of 1391 Hispanics, 557 African Americans, and 623 non-Hispanic Whites. (Meera Sangaramoorthy et al, Cancer Med., 2018)
Analysis of this study found that high intake of bean fiber, total beans (including protein and fiber rich garbanzo beans; other beans such as pinto kidney, black, red, lima, refried, peas; and black‐eyed peas), and total grains reduced the risk of breast cancer by 20%. The study also found that this reduction was more significant in estrogen receptor and progesterone receptor negative (ER-PR-) breast cancers, with the risk reductions ranging from 28 to 36%.
Coumestrol and Breast Cancer Risk – Swedish Study
Coumestrol is a phytoestrogen (plant compound with estrogenic properties) that are commonly found in chickpeas, split peas, lima beans, pinto beans and soybean sprouts. In a study published in 2008, the researchers evaluated the association between intake of dietary phytoestrogens including isoflavonoids, lignans and coumestrol and the risk of breast cancer subtypes based on the status of estrogen receptor (ER) and progesterone receptor (PR) in Swedish women. The assessment was done based on food questionnaire data obtained from the 1991/1992 prospective population-based cohort study, named the Scandinavian Women’s Lifestyle and Health Cohort Study, among 45,448 Swedish pre- and postmenopausal women. During a follow-up until December 2004, 1014 invasive breast cancers were reported. (Maria Hedelin et al, J Nutr., 2008)
The study found that compared to those who didn’t consume coumestrol, women who had an intermediate intake of coumestrol through taking protein rich peas, beans, lentils etc may be associated with a 50% reduced risk of estrogen receptor and progesterone receptor negative (ER-PR-) breast cancer. However, the study didn’t find any reduction in the risk of estrogen receptor and progesterone receptor positive breast cancers.
Legume Intake and Colorectal Cancer Risk
Meta-Analysis by Researchers from Wuhan, China
In a study published in 2015, researchers from Wuhan, China carried out a meta-analysis to evaluate the association between legume consumption and the risk of colorectal cancer. The data for the analysis was taken from 14 population based studies which were obtained based on literature search in Medline and Embase databases till December 2014. A total of 1,903,459 participants and 12,261 cases who contributed 11,628,960 person-years were included in these studies. (Beibei Zhu et al, Sci Rep. 2015)
The meta-analysis found that a higher consumption of legumes such as peas, beans and soybeans may be associated with a reduced risk of Colorectal Cancer, especially in Asians.
Meta-Analysis by Researchers from Shanghai, People’s Republic of China
In a study published in 2013, the researchers from Shanghai, China carried out a meta-analysis to evaluate the association between intake of legumes such as peas, beans and soybeans and the risk of colorectal cancer. The data was obtained from 3 population based/cohort and 11 case control studies with 8,380 cases and a total of 101,856 participants, through a systematic search of The Cochrane Library, MEDLINE and Embase bibliographic databases between January 1, 1966 and April 1, 2013. (Yunqian Wang et al, PLoS One., 2013)
The meta-analysis showed that a higher intake of legumes may be associated with a significant reduction in the risk of colorectal adenoma. However, the researchers suggested further studies to confirm this association.
The Adventist Health Study
In a study published in 2011, the researchers evaluated the association between intake of foods such as cooked green vegetables, dried fruits, legumes, and brown rice and the risk of colorectal polyps. For this, the data was obtained from dietary and lifestyle questionnaires from 2 cohort studies named the Adventist Health Study-1 (AHS-1) from 1976–1977 and the Adventist Health Study-2 (AHS-2) from 2002–2004. During the 26-yr follow-up since enrollment into the AHS-1, a total of 441 new cases of rectal/colon polyps were reported. (Yessenia M Tantamango et al, Nutr Cancer., 2011)
The analysis found that consumption of protein and fiber rich legumes at least 3 times per week may reduce the risk of colorectal polyps by 33%.
In short, these studies indicate that legume (such as peas, beans, lentils etc) intake may be associated with a reduced risk of colorectal cancer.
Legume Intake and Prostate Cancer Risk
Study by Wenzhou Medical University and Zhejiang University
In a study published in 2017, the researchers from Wenzhou Medical University and Zhejiang University, China carried out a meta-analysis to evaluate the association between legume intake and risk of prostate cancer. Data for this analysis was taken from 10 articles that included 8 population based/cohort studies with 281,034 individuals and 10,234 incident cases. These studies were obtained based on a systematic literature search in the PubMed and Web of Science databases till June 2016. (Jie Li et al, Oncotarget., 2017)
The meta-analysis found that for each 20 grams per day increment of legume intake, the risk of prostate cancer was reduced by 3.7%. The study concluded that a high intake of legumes may be associated with a reduced risk of prostate cancer.
Multiethnic Cohort Study in Hawaii and Los Angeles
In a study published in 2008, the researchers evaluated the association between legume, soy and isoflavone intake and the risk of prostate cancer. For the analysis, the data was obtained using a food frequency questionnaire in the Multiethnic Cohort Study in Hawaii and Los Angeles from 1993-1996, which included 82,483 men. During an average follow-up period of 8 years, 4404 prostate cancer cases including 1,278 nonlocalized or high-grade cases were reported. (Song-Yi Park et al, Int J Cancer., 2008)
The study found that compared to men with lowest intake of legumes, there was 11% reduction of total prostate cancer and 26% reduction of non-localized or high-grade cancer in those with the highest intake of legumes. The researchers concluded that legume intake may be associated with a moderate reduction in prostate cancer risk.
A previous study carried out by the same researchers had also suggested that consumption of legumes such as peas, beans, lentils, soybeans etc may be associated with a reduced risk of prostate cancer. (L N Kolonel et al, Cancer Epidemiol Biomarkers Prev., 2000)
Legume Intake and Endometrial Cancer Risk
In a study published in 2012, the researchers from the University of Hawaii Cancer Center, Los Angeles, evaluated the association between legume, soy, tofu and isoflavone intake and the risk of endometrial cancer in postmenopausal women. Diet data was obtained from 46027 post-menopausal women who were recruited in the Multiethnic Cohort (MEC) Study between August 1993 and August 1996. During a mean follow-up period of 13.6 years, a total of 489 endometrial cancer cases were identified. (Nicholas J Ollberding et al, J Natl Cancer Inst., 2012)
The study found that total isoflavone intake, daidzein intake and genistein intake may be associated with a reduced risk of endometrial cancer. However, the study found no significant association between increased intake of legumes and the risk of endometrial cancer.
Conclusion
Different population based studies indicate that consumption of protein and fiber rich foods such as legumes or pulses including peas, beans and lentils may be associated with a reduced risk of specific cancers such as breast, colorectal and prostate cancer. However, a population based study found that higher intake of leguminous foods such as peas, beans and lentils may not reduce the risk of endometrial cancer.
The American Institute of Cancer Research/World Cancer Research Fund Cancer also recommends including legume foods (peas, beans and lentils) along with whole grains, vegetables and fruits as a major part of our daily diet for cancer prevention. The health benefits of protein and fiber rich peas, beans and lentils also include reduction in heart diseases, diabetes, cholesterol and constipation, promoting weight loss, improving blood pressure, and so on. In short, including right quantities of low-fat, high protein legumes as part of a healthy diet may be beneficial.
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