Chapter 9.8

9.9 - Legumes and seeds as folate sources for pregnant women

Nick Moroz, University of Guelph, Canada

Suggested citation for this chapter.

Moroz,N. (2022) Legumes and seeds as folate sources for pregnant women, The Encyclopedia for Small Scale Farmers. Editor, M.N. Raizada, University of Guelph, Canada. http://www.farmpedia.org

Introduction to Legumes and Pulses

Legumes, known for their podded fruits and unique flower structure, consist of many staple crops of the bean and pea family that are mainly grown for their grain seed, which is called a pulse (Graham & Vance, 2003). Legumes include chickpeas, beans, lentils, peanuts, and more podded plants (Messina, 1999). Legumes also play an important role in traditional diets in many regions of the world (Messina, 1999). Legumes play an essential role in global soil nitrogen levels as most legumes have symbiotic nitrogen-fixing bacteria that grow in root structures called nodules and ‘fix-nitrogen’ from the air (Herridge, Peoples, & Boddey, 2008). As such, legumes are important for crop rotation, soil health, and high in protein content.

Pulses simply refer to the dried grain seed of any particular legume and are separate from leguminous oil seeds by their lower fat content in comparison (WHO/FAO, 2007). Pulses are an important source of energy, dietary protein, fibre, minerals and vitamins required for healthy livelihoods (Boye, Zare, & Pletch, 2010). Pulses are a vital source of dietary protein for a large portion of the world’s population, especially in regions where consumption of animal protein is limited by scarcity or self-imposed by cultural and religious factors (Boye et al., 2010). Nutritionally, pulses contain high amounts of protein (18-32%) and essential amino acids that might not be readily available, gaining pulses recent attention for their potential to fight malnutrition and disease (Boye et al., 2010).

The diets of subsistence level farmers in Africa and South Asia usually contain an adequate supply of carbohydrates through readily accessible grain products (maize, rice, etc.) but are often low in protein content (Broughton et al., 2003). Good supply of dietary proteins are often found in animal products, but scarcity of these products can prevent adequate protein intake (Broughton et al., 2003). Legumes are a notable solution to a lack of protein access, as legumes can provide the protein necessary for a health diet when other sources are unavailable (Broughton et al., 2003). In fact, dietary proteins are mainly acquired from legumes/pulses in many parts of the world (Broughton et al., 2003). By complementing other foods that are a primary source of carbohydrates, legumes that provide dietary proteins fulfill many human nutritional needs (Broughton et al., 2003).

Often a mono-carbohydrate diet of a single cereal grain is indicative of a population that is malnourished because cereals lacks the protein, vitamins, and minerals required for a healthy diet (Boye et al., 2010). However, pulses are normally high in protein, vitamin, and mineral composition. Cereals provide adequate carbohydrates but lack in protein, whereas pulses often provide adequate protein but lack in carbohydrates (Boye et al., 2010). Complementing locally grown grains with pulses and blending the different nutritional advantages of these crops could potentially address protein malnutrition problems worldwide (Boye et al., 2010). Legumes and cereal combinations in cultural diets have been key to survival of many peoples, and these combinations in cultural foods can be around the globe (FAO, 2016). Often, a diverse diet that includes various legumes, cereals, fruits, and vegetables, each providing its unique nutrient supply, provides the best chance for adequate nutrition in all required nutrients for human health.

Of vital importance, pulses are an important source of dietary minerals, with the potential to provide all 15 essential minerals required in a human diet if consuming adequate and diverse amounts (Wang et al., 2003). It should be noted that the mineral concentrations of minerals key to human metabolism (Fe, Zn, Ca, etc.) are low compared to animal food products (Wang et al., 2003).

The Common Bean: A Case Study

The common bean (Phaseolus vulgaris L.) is the most widely directly consumed grain legume in humans (Broughton et al., 2003). Global production exceeds 23 million metric tonnes and is twice that of the chickpea, the second most important grain legume (Broughton et al., 2003). The common bean represents half the grain legumes consumed globally, despite having lower than standard yields and sub-optimal seed quality (Broughton et al., 2003). It is the primary source of protein for humans in Mexico and Brazil (Broughton et al., 2003). Countries in Africa, such as Rwanda and Burundi, have reported that average national consumption of beans is greater than 40 kg per person per year, providing the second most important source of protein and third most important source of calories within these nations (Broughton et al., 2003). The high protein and mineral content of beans, especially in Fe and Zn, is important in areas with a high prevalence of micronutrient deficiencies, and should be complemented with starchy grains such as maize or root crops (Broughton et al., 2003). Beans are a major staple crop of eastern and southern Africa, often grown by resource-poor farmers (Broughton et al., 2003).

Legumes are High in Protein Content

As pulses are a rich source of protein, they contain high amounts of essential amino acids, including lysine, aspartic acid, and arginine (Boye et al., 2010). Pulses provide a well-balanced amino acid intake when paired with cereals and other foods rich in tryptophan and amino acids containing sulfur, as these metabolites are less prevalent in pulses (Boye et al., 2010). Table 1.1 shows that pulses are very high in protein content and as contain significant amounts of caloric energy, while some pulses are also rich in fats. In addition to their nutritional properties, pulse proteins provide water holding and fat binding functional properties that are also beneficial (Boye et al., 2010). Finally, fava beans are notable, and included in table 1.1 due to their drought resistance.

Legumes Complement Cereals that are low in Protein and Essential Amino Acids

Proteins in legumes such as beans can be predominantly stored as the protein phaseolin, a key indicator of the quality of bean seeds (Broughton et al., 2003). Phaseolin and many proteins in the legume family are deficient in amino acids that contain sulfur, including methionine (Broughton et al., 2003). The proteins contained in the seeds of cereals often contain these sulfur-containing amino acids, but are themselves deficient in other essential amino acids that are highly concentrated in pulses (Broughton et al., 2003). This is why a combined consumption of cereals and legumes can prevent nutritional deficiencies (Broughton et al., 2003). A balanced diet that provides all the essential nutrients occurs when cereals and legumes are consumed in a portion ratio of 2-cereal portions for every 1-legume portion (Broughton et al., 2003). As legume yields are often low, increased legume production to fulfill this nutritional ratio would benefit millions of malnourished people worldwide (Broughton et al., 2003).

Table 1.2 shows that pulses are high in amino acids that are not as prevalent in cereals, notably lysine and arginine, in which lysine is an essential amino acid. This table also shows how methionine levels (a sulfur-containing amino acid) are lower in pulses and must be obtained from alternative foods such as cereals.

Minerals are Highly Concentrated in Legumes and the Seed Coat of Cereals

Cereals are often consumed as an energy source while legumes provide micronutrients for human nutrition (Broughton et al., 2003). Legumes are a much greater source of micronutrients when compared to cereals because of their higher natural abundance of minerals and because many cereals have their seed coat remove prior to eating (Broughton et al., 2003). Polishing of cereals and removing the seed coat, also known as the bran, reduces the mineral content as these coatings contain a significant amount of minerals, giving this coating its rigid structure (Broughton et al., 2003). Conversely, many pulses are consumed whole, without the removal of the their outer layers, conserving their mineral content (Broughton et al., 2003). For example, beans supply high levels of iron, phosphorus, magnesium, and moderate levels of zinc, calcium and other minerals (Broughton et al., 2003). Beans often provide 10-20% of the adult requirement for many nutrients for those with restricted dietary consumption, defined as 15-20 kg/year (Broughton et al., 2003). Therefore, legume consumption in combination with cereals should be considered in addressing micronutrient deficiencies worldwide (Broughton et al., 2003).

Increasing the seed mineral density of grain legumes (pulses) is of interest, as these foods can contain all 15 essential minerals require in human nutrition (Wang et al., 2003). However, some mineral deficiencies, notably Fe and Zn deficiency, can still be prevalence in regions where legumes provide a considerable portion of the human diet (Wang et al., 2003). One possible solution is smaller pulses, or legume-seeds. Smaller seeds have a higher seed coat surface area in comparison to the seed volume. As the seed coat is the part of the seed that has the highest concentration of minerals, consumption of smaller seeds would mean more mineral intake per volume of pulses consumed. Additionally, research to understand how minerals move into has grained increased interest in order to optimize mineral-uptake conditions (Wang et al., 2003).

Antinutrients, Diet Composition, and Nutrient Bioavailability/Digestibility

Pulses seeds contain some undesirable “antinutrients” that interfere with normal protein digestibility and uptake of micronutrients (Boye et al., 2010). For example, phytic acid and trypsin inhibitors are antinutrients in some pulses that reduce micronutrient uptake and protein digestibility, respectively (Campos-Vega, Loarca-Piña, & Oomah, 2010; Welch & Graham, 2004). There are numerous other antinutrients in plant-foods that can impair human nutrition, but there are also many nutrients that increase of vitamins and minerals uptake and stimulate nutrition (Welch & Graham, 2004). Additionally, antinutrients may have some beneficial properties for human health, complicating the literature (Campos-Vega et al., 2010; Welch & Graham, 2004). Most legumes are mainly composed of proteins that are highly digestible and have high protein content (Boye et al., 2010).

The composition of one’s diet is highly important in determining the bioavailability of nutrients found in plant foods (Welch & Graham, 2004). Plant food processing and preparation techniques can influence the amount of bioavailable micronutrients, sometime reducing the nutrient uptake (Welch & Graham, 2004). An example of this is combining foods rich in animal proteins (e.g. beef, poultry) with plant foods that have high antinutrient concentrations (e.g. phytic acid), which can lower the uptake of Fe and Zn from the meal (Welch & Graham, 2004).

Resources Moving Forward

FAO Kids – Health benefits of pulses, clearly outlined. Retrieved from: http://www.fao.org/documents/card/en/c/37152a05-f15f-4373-a3f3-e355ac6cc83e/

What are Pulses? – 2016 International Year of Pulses. Retrieved from: http://iyp2016.org/resources/what-are-pulses

Importance of Legumes in African Culture, N2Africa. Retrieved from: http://www.n2africa.org/rationale/ImportanceLegumes

References

1.Boye, J., Zare, F., & Pletch, A. (2010). Pulse proteins: processing, characterization, functional properties and applications in food and feed. Food Research International, 43(2), 414-431.

2.Broughton, W. J., Hernandez, G., Blair, M., Beebe, S., Gepts, P., & Vanderleyden, J. (2003). Beans (Phaseolus spp.)–model food legumes. Plant and soil, 252(1), 55-128.

3.Campos-Vega, R., Loarca-Piña, G., & Oomah, B. D. (2010). Minor components of pulses and their potential impact on human health. Food research international, 43(2), 461-482.

4.FAO. (2016). FAO Kids – Health benefits of pulses. Rome, Food and Agricultural Organization of the United Nations. Retrieved from: http://www.fao.org/documents/card/en/c/37152a05-f15f-4373-a3f3-e355ac6cc83e/

5.Graham, P. H., & Vance, C. P. (2003). Legumes: importance and constraints to greater use. Plant physiology, 131(3), 872-877.

6.Herridge, D. F., Peoples, M. B., & Boddey, R. M. (2008). Global inputs of biological nitrogen fixation in agricultural systems. Plant and Soil, 311(1-2), 1-18.

7.Messina, M. J. (1999). Legumes and soybeans: overview of their nutritional profiles and health effects. The American journal of clinical nutrition, 70(3), 439-450.

8.Wang, T. L., Domoney, C., Hedley, C. L., Casey, R., & Grusak, M. A. (2003). Can we improve the nutritional quality of legume seeds?. Plant Physiology, 131(3), 886-891.

9.Welch, R. M., & Graham, R. D. (2004). Breeding for micronutrients in staple food crops from a human nutrition perspective. Journal of experimental botany, 55(396), 353-364.

10.WHO/FAO, Joint Committee. (2007). Codex Alimentarius. Cereals, pulses, legumes and vegetable proteins. 1st Edition. FAO, Rome, Italy.