Abstract

Pulses eaten worldwide include dry beans, lentils, and peas. They are leguminous crops that are grouped together as they are high protein and low fat. They have a high profile as a food because in addition to providing needed micronutrients and protein, they are environmentally friendly. Pulses have many benefits, such as improving soil fertility through nitrogen fixation, reducing greenhouse gas emissions, and contributing to sustainable agricultural practices. However, pulses contain “anti-nutrients”: those that cause harm to the intestinal tract such as lectins and fermentable oligosaccharides, monosaccharides and polyols; (FODMAPs), and those that inhibit absorption of important microminerals such as iron and zinc, such as phytate and polyphenols. Thus, in the Global South, risk of micromineral deficiency dampens interest in pulses as a protein source. In the Global North, pulses are lauded as a plant-based protein yet caution is expressed over health risks such as inflammatory bowel syndrome (IBS). Solutions to these concerns are described and discussed.

Keywords:Pulses; Legumes; Plant-based protein; Micronutrients; Anti-nutrients; Food guides; Phytate

Abbreviations:IBS: Inflammatory bowel syndrome; FODMAP: fermentable oligosaccharides, disaccharides, monosaccharides and polyols; RCT: randomized controlled trial; T2DM: type 2 diabetes mellitus

Introduction

Pulses are considered a subgroup of legumes due to their unique nutritional composition. As shown in Table 1, common edible pulses are high in protein, low in fat, and are a good source of dietary fiber as well as many important vitamins (e.g., folate) and minerals (e.g., iron, zinc, calcium) [1]. As plant-based foods they are low in sodium and high in potassium. These nutrient characteristics are the basis for many of the health benefits that have been described for pulses [2, 3]. The Food and Agriculture Organization (FAO) of the United Nations designated 2016 as the International Year of Pulses to raise awareness about the importance of pulses in global food security, nutrition, and sustainable agriculture. The Year of Pulses aimed to promote the consumption and production of pulses worldwide and raise awareness of their nutritional value, health benefits, and contributions to sustainable food systems. Messaging was done in every country yet it must be recognized that there would be differences between how the Global North promoted pulses in contrast to the Global South. The Global North generally refers to the more economically developed and industrialized countries located primarily in North America, Europe, and parts of Asia. These countries are often characterized by higher levels of wealth, education, and healthcare. The Global South refers to the less economically developed countries, primarily located in Africa, Asia, Latin America, and the Caribbean. These countries often face significant challenges in terms of poverty, limited access to education and healthcare. Thus, differences in priority areas would be expected to exist. Using Canada (Global North) and Ethiopia (Global South) as examples, this paper discusses the similarities and differences in how pulses are promoted between the Global North and Global South.

Discussion

Canada-example of a global north country

Canadian farmers grow a lot of pulses but its citizens eat very little. Table 2 shows the mean intake of servings of cooked pulses by Canadians of all ages, which was only 0.3 servings in 2004 and 0.4 servings in 2015 on a per capita basis [4]. In Table 2, pulses are part of the food grouping called legumes, nuts and seeds. Despite increased interest in pulses as plant-based protein foods, intake in low and is mainly due to immigrant groups such as Chinese- Canadians and Indo-Canadians. Canada’s Food Guide was revised in 2019 to have only three food groups: Vegetables and fruit, Whole grains, and Protein [5]. The Protein food group consists of animal source foods such as meat, fish, poultry, eggs, shellfish and dairy products. It was previously called Meat and Alternatives, and the change reflected a move towards having more plantbased foods in the Canadian diet. In this new guide, pulses are in the newly named protein group which is a mix of animal-based and plant-based protein foods. In contrast, pulses are in both the Protein group and the Vegetable group in the United States [6].

Ethiopia-example of a global south country

Ethiopia is a significant pulse producer [7]. One of Ethiopia’s signature national dishes is shiro stew, which is a chickpea food eaten with the national teff-based bread injera. Yet Ethiopians do not eat a lot of pulses, as shown in the 2013 survey of food consumption as presented in Table 3 [8]. As a percentage of total weight of foods eaten, consumption of legumes and nuts can be negligible in some regions of Ethiopia, and overall intake can be one-tenth that of cereals. In part, as a result of this low intake of legumes, in 2022 the Federal Government of Ethiopia issued foodbased dietary guidelines to encourage intake of pulses. It states as key messages to 1. Eat a variety of foods every day including fruits, vegetables, legumes and animal foods, and 2. Eat legumes such as beans, chickpeas, peas and lentils every day [9]. The rationale for emphasizing legumes (most of which are pulses) is for their health benefits.

Health benefits of pulses

Much research has been conducted on the health benefits of pulses. Table 4 provides a summary of the three most commonly cited health benefits that are major concerns in countries in both the Global North and Global South as initially outlined by Mudryj and Aukema [2]. First, pulses are a good to excellent source of many nutrients of concern. Evidence for this benefit is found from national survey data in which pulse consumers are shown to have better nutrient densities that non-pulse consumers [10]. In Global South countries, such as Ethiopia, national surveys show low intakes of foods containing adequate amounts of protein, iron, zinc and many vitamins [8]. A reduction in the risk of chronic disease is the second health benefit. Those diseases include cardiovascular disease, and here the fact that pulses are low in fat and high in dietary fiber may be the major reasons for this, as well as having a good content of bioactive molecules such as isoflavones and flavonols. Hypertension causing stroke may be mitigated by pulse intake through the favourable sodium-potassium ratio. Risk of colon cancer is lessened with pulse intake and again, the high fiber content may be the major contributing factor. Finally, a reduction in risk of type 2 diabetes mellitus (T2DM) is seen when foods having low glycemic index such as pulses are consumed. And in terms of treatment, recently a pulse-rich diet improved glycemic parameters in patients having T2DM [11].

Evidence for these effects are mainly seen by studies that are randomized controlled trials (RTCs), as well as longitudinal studies (cohorts). A third health benefit is that of reducing the risk of being overweight or obese. Studies demonstrating this effect are often cross-sectional in design, which can be problematic as people in the normal range of BMI may choose pulse-based diets thus causing bias in the results. However, recent studies are focussing on satiety as a factor in causing weight gain. A small study of bread formulated to contain 80% white flour and 20% pea flour showed significant reductions in indices of satiety such as fullness after ingestion, compared to 100% white flour in controlled experiments [12]. While more research is needed on using pulse foods or foods formulated to contain pulse isolates, this is a promising area for further study.

Health risks of pulse overconsumption

There are naturally occurring compounds found in raw plants that are referred to as “anti-nutrients” because they can cause health concerns such as gastrointestinal health and/or interfere with normal metabolism by blocking absorption of other nutrients. They are present in small quantities and usually do not pose significant health risks, however, excessive consumption or improper preparation of certain foods can lead to potential adverse effects. Further, a recent review suggests anti-nutrients are not a problem as many if not all of these compounds have been shown to have health effects, often as prebiotics or anti-cancer agents [13]. The four major anti-nutrients in pulses are shown in Table 5: fermentable oligosaccharides (FODMAPs), lectins (e.g. phytohemagglutinin), phytate, and polyphenols including tannins.

The FODMAPs are low molecular weight non-digestible carbohydrates that are associated with contributing to irritable bowel syndrome (IBS). On the other hand, these non-digestible carbohydrates are prebiotics (soluble fibres) which encourage the growth and maintenance of a healthy microbiome. With proper processing such as soaking, cooking in high heat, fermentation or germination, FODMAP content is reduced. Canned pulses have very low contents of FODMAPs [14]. For persons who have identified pulses as a source of their IBS, adhering to FODMAP guidance is imperative. While consumers in Global North countries can purchase processed pulses, commonly as canned, those in Global South countries can apply home-based processing primarily through soaking and germination [15]. Lectins are proteins that bind to carbohydrates, found primarily in raw pulses and in some whole grains. They can interfere with nutrient absorption and may cause digestive issues in some individuals. The concern is mainly for lectin-sensitive individuals who may lack enzymes capable of breaking down lectins. Raw or inadequately heat-treated pulses retain their lectin activity, which can lead to deleterious gastrointestinal and systematic effects with consumption [14]. Proper cooking and soaking can help reduce lectin content.

Phytate is found in pulses as well as seeds, nuts, and grains. Due to its phosphate content phytate can bind to positively charged cationic minerals in the intestine such as iron and zinc thus reducing their bioavailability. The harmful effect on nutritional status, however, is dependent upon dietary adequacy. A study by Hunt et al. [16] showed that zinc absorption was only reduced in subjects on a high phytate diet if their intake of zinc was below the RDA; those on a high phytate diet but with adequate zinc intake showed no decrease in zinc absorption. Thus, phytate would be more deleterious in the Global South such as Ethiopia where zinc intakes are low due to lack of foods such as meat and legumes [8]. Another factor in phytate-reduced micromineral absorption is processing, by which soaking or germination can reduce phytate levels [15]. Dietary phytate is not of a concern in the Global North as few are inadequate in iron or zinc excepting those eating exclusively plant-based diets low in legumes [17]. Polyphenols in plants are large molecules having diverse functions that are concentrated throughout the plant, where they function in defending plants against pathogens and pests [13]. Polyphenols are found in pulses, particularly in seed hulls. Tannins are a group of polyphenols that are capable of binding divalent cations such as iron, rendering them less bioavailable [15]. In the Global South, if pulses are consumed without dehulling, the decrease in mineral absorption is more severe than in Global North countries where other, more bioavailable sources of iron and zinc may be ingested, for example meat. Similar to phytate, soaking or germination can reduce polyphenol effects on mineral absorption [15].

Conclusion

Pulses are foods with health benefits for both the Global North and Global South. However, current intakes need improvement. For the Global South, more pulses in the diets will improve protein intake as well and micronutrient intake in a cereal-based diet. Governments such as Ethiopia [9] are making pulse foods central to food-based guidelines to provide plant-based proteins that are complementary to cereal proteins. In the Global North, a move to more plant-based proteins replacing animal protein sources is advocated [18]. Further, the low fat and high fiber content of pulses contribute to reduction of risk of many chronic diseases. Pulses provide many key minerals including iron and zinc which are often needed in Global South countries having primarily cereal-based diets, in order to provide for adequate growth and development of children and adolescents, and for women’s health. In general, anti-nutrients found in pulses are not issues when pulses are adequately processed using soaking, germination, and fermentation, or are purchased as canned. Overall, continued encouragement of pulse food consumption in both Global North and Global South is highly recommended.

Acknowledgement

The author is grateful to Dr Dilrukshi (Dil) Thavarajah, Professor, Pulse Quality and Nutritional Breeding/Clemson University, USA for encouraging the author to pursue this topic.

Conflict of Interest

The author has no economical conflict or conflict of interest.

References

1. Health Canada. Canadian Nutrient File.
2. Mudryj AN, Yu N, Aukema HM (2014) Nutritional and health benefits of pulses. Appl Physiol Nutr Metab 39(11): 1197-1204.
3. Agarwal S, Fulgoni VL (2023) Effect of adding pulses to replace protein foods and refined grains in healthy dietary patterns. Nutrients 15(20): 1-12.
4. Tugault Lafleur CN, Black JL (2019) Differences in the quantity and types of foods and beverages consumed by Canadians between 2004 and 2015. Nutrients 11(3): 1-24.
5. Health Canada Food Guide (2019).
6. Ford K, Bobroff L, Whiting SJ (2019) Where do pulses fit in dietary guidance? In Dahl WJ (ed) Health Benefits of Pulses Springer Pp: 35-42.
7. Teferra TF (2021) Advanced and feasible pulses processing technologies for Ethiopia to achieve better economic and nutritional goals: A review. Heliyon 7(7): 1-9.
8. Ethiopian Public Health Institute (2013) Ethiopian National Food Consumption Survey, published by Ethiopian Public Health Institute, Addis Ababa, Ethiopia.
9. Federal Government of Ethiopia, Ministry of Health, Ethiopian Public Health Institute (2022). Ethiopia: Food-Based Dietary Guidelines-2022. Addis Ababa, Ethiopia.
10. Mitchell DC, Marinangeli CPF, Pigat S, Bompola F, Campbell J, et al. (2021) Pulse intake improves nutrient density among US adult consumers. Nutrients 13(8): 1-9
11. Hosseinpour Niazi S, Mirmiran P, Hadaegh F, Mahdavi M, Khalili D, et al. (2022) Improvement of glycemic indices by a hypocaloric legume-based DASH diet in adults with type 2 diabetes: a randomized controlled trial. Eur J Nutr 61(6): 3037-3049.
12. Fahmi R, Blewett H, Stebbing JA, Olson N, Rylan D, et al. (2022) Acute effects of split pea-enriched white pan bread on postprandial glycemic and satiety responses in healthy volunteers a randomized crossover trial. Foods (Basel, Switzerland) 11(7): 1-22.
13. Petroski W, Minich DM (2020) Is there such a thing as "anti-nutrients"? A narrative review of perceived problematic plant compounds. Nutrients 12(10): 1-32.
14. Dahl WJ, Alvarez MM (2019) Whole pulses and pulse fiber: role in modulating gastrointestinal function and the microbiome. In Health Benefits of Pulses Dahl WJ (Ed) Springer Pp: 91-108.
15. Whiting SJ, Berhanu G, Haileslassie HA, Henry CJ (2019) Pulses and Mineral Bioavailability in Low Income Countries. In Dahl WJ (ed) Health Benefits of Pulses Springer Pp: 43-53.
16. Hunt JR, Beiseigel JM, Johnson LK (2008) Adaptation in human zinc absorption as influenced by dietary zinc and bioavailability. Am J Clin Nutr 87(5): 1336-1345.
17. Neufingerl N, Eilander A (2023) Nutrient intake and status in children and adolescents consuming plant-based diets compared to meat-eaters: a systematic review. Nutrients 15(20): 1-26.
18. Willett W, Rockstrom J, Loken B, Springmann M, Lang T, et al. (2019) Food in the Anthropocene: the EAT-Lancet Commission on healthy diets from sustainable food systems. Lancet 393(10170): 447-492.