The world population is constantly growing, and the current global population of 8 billion (as of mid-November 2022) is expected to increase to 9.7 billion in 2050 [1]. Increased population pairs with a predicted higher demand for food. Total food demand, including that from protein sources, is expected to increase from 35% in 2010 to 56% in 2050 [2]. In the past decade, consumers’ interest in increasing protein intake from alternative sources, including plant-based types such as legume-derived ones, has increased. This request has been driven by factors including the relatively lower carbon footprint associated with leguminous crop cultivation, with its fewer deleterious effects on climate change compared to cattle breeding [3,4,5], health reasons [3,5], and the relatively high cost of meat compared to legume-derived proteins [6], especially in Southeast Asia and Sub-Saharan Africa. Moreover, the increased sustainability associated with the production of plant crops, including legume proteins, should be taken into account [7,8]. Globally, different legume types are widely distributed.

The Food and Agriculture Organization of the United Nations (FAO) recognizes ten main types of legumes: dry beans including soybean, dry broad beans, dry peas, chickpeas, cowpeas, pigeon peas, lentils, Bambara beans, vetches, and lupins [9]. Additionally, there are “minor” legumes that are less commonly used internationally [9]. The four most commonly used species for food purposes, marketed in both dry and hydrated forms, are beans, lentils, peas, and chickpeas. Leguminous crops are resilient towards climate changes and possess an inherent ability to fix atmospheric nitrogen in the soil leading to improvement in soil fertility [10]. In terms of nutritional composition, legumes contain a high concentration of protein (23.7–25.9 g/100 g dry beans and 8.23–9.01 g/100 g for cooked beans), a high content of soluble and insoluble fibers (4.1–4.3 g/100 g dry beans and 7.0–10.5 g/100 g for cooked beans), a low lipid content (except for soybeans), are free of saturated fats and cholesterol, and are good sources of B-group vitamins, iron, magnesium, copper, selenium, calcium, potassium, zinc, and manganese [11,12]. Legumes generally have a low caloric density and low glycemic index, due to their high fiber composition [12].

According to European and American nutritional guidelines, legumes are an important part of a healthy diet [13,14]. The European Food Safety Authority [15] states that legumes represent a valid source of protein and that they are essential for a healthy diet. It has been recommended that adults consume at least 20–25 g of protein from plant sources per day [13]. Due to the excellent nutritional profile and health-promoting effect associated with legume consumption, they represent an important component of several dietary guidelines. For example, increased consumption of legumes has been encouraged as part of the Mediterranean and the DASH dietary pattern guidelines. Several epidemiological studies demonstrated improved outcomes in cardiovascular disease, diabetes, cancer, Alzheimer’s disease, and Parkinson’s disease following strict adherence to the Mediterranean and DASH diet, both including legumes [16]. The DASH diet recommends an intake of about four-to-five servings of legumes per week for a 2000-calorie diet to effectively control blood pressure [17]. Additionally, the 2020–2025 Dietary Guidelines for Americans recommend legumes as part of a healthy dietary pattern, stating that “legumes provide protein, dietary fiber, and a variety of vitamins and minerals, including iron, potassium, and folate” [14]. Legumes are a healthy and versatile food option for people following specific diets, such as those for people with gluten intolerance [18] or vegetarianism [19]. This has been largely attributed to their gluten-free nature [20]. Furthermore, legumes combined with cereals provide all of the essential amino acids and represent a valuable one-dish meal for vegans or vegetarians. Legumes are thus used in complementary formulations in cereal-based products, due to their high amino acid lysine content which in cereals is deficient [21].

Hughes et al. [22] recently showed that there was a general global decline in beans and legume consumption, according to data derived from the Global Dietary Database (“GDD 2018”) in June 2022. The authors evaluated the national intake of legumes and beans considering the 50 g/day [23,24] target, which has been established according to several meta-analyses as the ideal intake required to reduce mortality and morbidity outcomes [23,24]. The general decline observed could be attributed to the lack of clear recommendations on the appropriate quantity and serving size of beans and other legume-based products despite the availability of national food-based dietary guidelines, as observed in Australia [25]. This is because most of the food-based dietary guidelines group together legumes with seeds, vegetables, and starchy staples [25]. In a recent cross-national survey conducted in Europe, consumers from Poland, Spain, and Germany reported that digestion challenges associated with legume consumption were an important barrier that restricts legume intake. In Danish and UK consumers, the lack of available easy-to-cook legume and legume-based products was the underpinning barrier to their consumption [26]. Consequently, there is a need to implement strategies that could promote legume intake in the population. This could lead to improved health outcomes and increased sustainable food supply, resulting in a lower carbon footprint and leading to better environmental sustainability. In 2015, Polak et al. [27] reviewed the health effects and some culinary approaches that could be adopted to promote legume consumption. However, barriers and strategies to improve digestibility and overcome digestive challenges associated with legume intake, leading to increased consumption, have not been addressed. The present article therefore highlights the effects of cooking on the nutritional profile of legumes, underlines health effects associated with legume consumption, and, finally, examines strategies to improve the digestibility and nutritional profile of legumes. Additionally, the use of state-of-the-art educational and culinary approaches that could be exploited to improve legume intake are extensively discussed.

The nutritional composition of legumes influences their health-promoting properties, which is an important factor that can influence consumers’ consumption of legumes. Legumes are rich in protein and fiber. For example, according to the USDA Food Data Central database, protein and fiber content ranging from 19.0 to 36.0 g/100 g and from 9.0 to 25.0 g/100 g, respectively, for legumes including common beans, lentils, chickpeas, peas, broad beans, and soybeans have been reported [28].

The high protein content of legumes is a promising trait that makes them ideal candidates for product reformulation with foods that are generally lower in protein. It is important to note that protein addition would influence aliment techno-functional and sensorial properties when used in food product development. Although plant-based proteins are deemed second-class proteins, efforts to improve their digestibility could enable them to compete with those derived from animal sources. The relatively high fiber content [28] makes them promising for lowering the glycemic impact of foods when incorporated into other staple foods and could induce satiety. The cooking of legumes is essential as it impacts its digestibility and nutritional composition [29]. Storz et al. [30], recently, using a nationally representative sample of 9078, investigated the current sex distribution of cooking responsibilities in the United States of America. The authors reported that cooking duties are still being mostly performed by women. Consequently, women could be targeted for educational training efforts to promote legume consumption. The effect of cooking methods on the nutritional composition of some commonly consumed legumes will be discussed.

Margier et al. [31] investigated the effect of household cooking and canning on the nutrient profile of common legumes including kidney beans, white beans, chickpeas, and brown and green lentils. For the household cooking employed, the authors adopted household cooking methods protocol established by the French National Federation of Dry Legumes. The legumes were soaked in low-ionized water overnight at room temperature using a water-to-legume ratio of 5:1, with the exception of lentils. The legumes were drained of the water and cooking proceeded afterwards using a water-to-legume ratio of 2:1. Cooking duration was 25 min, 1 h 30 min, and 2 h for the lentils, kidney beans/white beans, and chickpeas, respectively. In the canning process, the pre-treatment method, which involved an overnight legume soaking in water at a ratio of 1:3, was employed. Blanching legumes at 90 °C for 5 min was carried out prior to transfer into a can with hot brine at a ratio of 195/236 (w/w). Sterilization of the legumes was carried out at 127 °C for 16 min in the can. The final step involved the cooling of the sterilized products to a temperature of 30 °C for 10 min. The authors stabilized the sterilized legumes by draining the water, rinsing the legumes in water, and subsequently freezing the legumes. The samples were freeze-dried and kept at a temperature of −80 °C until analysis. The results showed a general increase in the protein and fiber content of all the legumes cooked using the household cooking method compared to the canning method. Specifically, the protein and fiber content of kidney beans, white beans, chickpeas, and lentils increased by 30.30 and 43.97%, 17.78 and 33%, 17.44 and 21.95%, and 38.87 and 55.29%, respectively, when the household cooking method was used, compared to the sterilization process [31]. The general decrease in protein concentration of the cooked legumes compared with the raw types could be attributed to the loss of proteins into the cooking water, which could be considered part of the cooking losses.

Legumes, aside their rich nutrient profile, contain bioactive compounds that provide favorable health effects [32]. Bioactive compounds are mainly secondary plant metabolites that are synthesized by the plants to enable them to defend themselves from predators [33]. In legumes, bioactive compounds and other compounds are present as minor components and include polyphenols, saponins, enzymes inhibitors, and phytates (Figure 1). The bioactive compounds that are present in legumes provide favorable effects on health [34]. Consequent to this, legumes can be considered as “functional foods”, due to the presence of nutrients and bioactive compounds. Examples of bioactive compounds present as minor components of legumes and their potential health-promoting properties have been highlighted (Figure 1).

Recently, several systematic reviews and meta-analyses of prospective studies have established an inverse association between increased legume intake and cardiovascular (CVD) risk and its disease outcomes [35,36]. For example, increased consumer intake of legumes (≥50 g/day) was associated with a lower risk of coronary heart disease [23] and strokes [36]. CVD, A 6% decrease in CVD risk was associated with increased legume consumption [35]. The plausible reason associated with the improved CVD and coronary artery disease (CAD) outcomes following increased legume consumption could be attributed to the modulation of total cholesterol and low-density lipoprotein cholesterol (LDL-C) blood levels [37], which represent well known risk factors for CVD and CAD. The mechanisms of protection can be explained since fibers, particularly the soluble type from legumes, prevent bile acid recycling as bile acid is removed from the body through feces [38]. This subsequently increases the rate of cholesterol conversion into bile acids and results overall in lower cholesterol concentrations in the body. The second mechanism could involve the role of saponins in the legumes on the modulation of cholesterol levels. Saponins are secondary plant metabolites produced by legumes to provide defense against predatory attacks. Due to their intrinsic presence in legumes, upon legume consumption saponins are hydrolyzed by intestinal bacteria to form an insoluble complex. Saponin complexes interact with cholesterol molecules, impairing the formation of micelles, inhibiting lipase enzyme, and chelating bile acids with subsequent reduction in circulating cholesterol concentration through increased cholesterol conversion into bile acids [39]. Another mechanism could involve the production of short-chain fatty acids, including propionic and butyric acid, as a result of the fermentation of resistant starches from legume fibers [40]. Short-chain fatty acids (SCFAs) have been shown to inhibit hepatic cholesterol synthesis in animal models [41]. A relatively lower production of trimethylamine N-oxide (TMAO) by the gut microbiota following legume consumption was observed, as earlier reported, in comparison to animal-based protein sources deriving from fish or red meat [42,43]. The presence of trimethylamine N-oxide (TMAO) levels in the blood and urine has been established as an objective biomarker associated with increased risk of heart disease. The presence of specific concentrations of micronutrients, including low sodium, high magnesium, and potassium in legumes, may contribute to the reduction of arterial hypertension risk [44]. Legumes are low glycemic index foods with potential insulin-sensitizing effects [45,46,47]. Insulin inhibits the release of free fatty acids from adipose tissue, and this makes legumes impact positively on VLDL and LDL levels [48,49].

Legumes, due to their high fiber and resistant starch content, are effective in controlling postprandial glucose levels and insulin response when compared to other carbohydrate-containing foods [50]. Fiber increases satiety and decreases the absorption efficiency of fats and carbohydrates [51]. Soluble fiber reduces peak blood glucose because it increases the viscosity of the intestinal contents and hinders the absorption of monosaccharides [52], while insoluble dietary fiber modulates the release of gastric hormones and causes delayed absorption of monosaccharides [53].

Dietary plans involving the use of legumes in the medium to long term are desirable in individuals with type 2 diabetes mellitus due to their efficacy in controlling glycemic markers; however, in non-diabetic individuals, individuals with type 1 diabetes, and individuals with prediabetes, the evidence is still limited or contradictory and requires further long-term randomized controlled trials [54,55]. It has been observed that regular consumption of legumes may play an important role in reducing the risks associated with type 2 diabetes mellitus. In a recent systematic review of randomized, controlled trials [56] of individuals with and without diabetes, statistically significant effects were observed in the groups of subjects consuming diets high in legumes with regard to reductions in fasting blood glucose, glycosylated hemoglobin, and blood glucose two hours after a meal. In subjects with type 1 diabetes, the only statistically significant effect found was the decrease in blood glucose two hours after the meal. Improvements in glycemic control were consistently observed on the legume diet in diabetic individuals in several studies identified by this review. Diets containing legumes have also been associated with lower postprandial insulin levels [57]. Several studies [58,59] have also evaluated the effects of legume consumption on the risk of gestational diabetes. Pregnant women may benefit from a legume-based diet to prevent gestational diabetes [58]. Women who adopted a plant-based diet during pregnancy had a significantly reduced risk of developing gestational diabetes compared to women who followed a standard diet [59].

Due to their particular nutritional characteristics (high fiber and protein content, low glycemic index, low fat content), legumes can be considered a useful food to treat and prevent obesity and being overweight [60]. There are several mechanisms that can explain the weight loss associated with legumes. Some of their satiating properties can be attributed to the presence of fiber, which increases chewing time, delays gastric emptying, inhibits food intake, and stimulates early satiety signals. In addition, soluble fiber in the gastrointestinal lumen forms viscous gels that slow the passage of food through the digestive tract, contributing to the feeling of fullness [61]. The high protein content stimulates the secretion of the hormones cholecystokinin and GLP-1, which contribute to increased satiety [62]. The low glycemic index regulates the secretion of insulin and the blood concentration of glucose, thereby controlling the desire to eat. In addition, legumes contribute to weight loss through the reduced bioavailability of nutrients. High-fiber diets contribute to reduction in fat and protein absorption by reducing the physical contact of nutrients with the intestinal villi [61], by limiting intestinal absorption of nutrients through the formation of viscous gels due to soluble fiber, and by increasing intestinal transit speed due to insoluble fiber [63]. Another characteristic that contributes to making legumes appropriate aliment in weight loss diets is the quality of the carbohydrates: these foods contain a high quantity of amylose-type starch which, after cooking, undergoes the process of retrogradation and becomes more resistant to digestion, compared to amylopectin-type starch [64]. All these mechanisms involving fiber and resistant starches act synergistically to increase satiety, manage body weight, reduce glycemic response, and improve insulin sensitivity [65]. Cell-wall polysaccharides, oligosaccharides (raffinose, stachyose, and verbascose), and resistant starch are the main non-digestible carbohydrates in legumes that are fermented by intestinal bacteria into SCFAs, which are able to influence lipid metabolism and promote fat oxidation and energy expenditure [66].

Some studies have linked the consumption of legumes with a protective effect on certain types of cancer, such as colon, prostate, and breast cancer [67]. According to the World Cancer Research Fund/American Institute for Cancer Research [68], the high amounts of vitamins and minerals in legumes have been suggested to reduce the risk of developing cancer. In vivo studies with rats, in which pre-neoplastic lesions were caused by azoxymethane, showed that eating beans was associated with a lower risk of colon cancer [69]. Similar studies have been conducted to evaluate the effect of bean consumption on induced breast carcinogenesis in rats [70,71]. In the groups that consumed beans, there were dose-dependent reductions in the incidences of breast cancer compared to the control group. In addition, a dose-dependent reduction in the blood concentration of glucose, IGF1 (insulin-like growth factor), C-reactive protein, IL6, and increased apoptosis in mammary adenocarcinoma cells were found in the treated group.

The non-digestible fraction (resistant starch, insoluble fiber, and oligosaccharides) of many types of common beans possesses anti-proliferative activity and is able to induce apoptosis in colon cancer cells [34]. There are several micronutrients that contribute to the possible anti-cancer effect of legumes: trace elements such as zinc, which is associated with a reduction in oxidative stress and improved immune system functioning, and selenium which, due to its ability to inhibit the development of tumor cells in mouse models of cancer, could play a role in the prevention of breast, esophageal, and stomach cancer [43]. Saponins, protease inhibitors, phytates, and tannins appear to have anticarcinogenic activity due to their antioxidant and regulatory action on cell proliferation [72,73]. Protease inhibitors slow down the rate at which cancer cells divide and stop proteases, which kill nearby cells, from being released. Specifically, black beans contain a trypsin inhibitor that possesses anti-proliferative activity in vitro [74].

The high amounts of non-digestible oligosaccharides (raffinose, stachyose, and verbascose), resistant starch, and other non-starch polysaccharides in legumes contribute to the formation of SCFAs in the large intestine. This confers to these foods “prebiotic potential” by changing the composition of the intestinal microbiota and increasing the growth of Bifidobacteria. Among the short-chain fatty acids, in particular propionate, has been shown to decrease cholesterol levels, reduce endogenous fatty acid synthesis, and promote satiety [66]. SCFAs can influence enterocyte growth because butyrate is their main source of energy and appears to protect against cancer with anti-inflammatory and anti-tumor effects on colon cancer cells, and also affects mineral availability because a lower pH in the colon allows calcium and magnesium to dissolve more easily [75]. To figure out if a diet high in legumes can change the gut bacteria in a good way, more research needs to be carried out to investigate their prebiotic potential.

Since oxidative stress and inflammation are recognized as playing crucial roles in the onset of age-related and chronic diseases, they may be fruitful dietary targets for preventing illness [76]. Legumes contain polyphenols in the form of phenolic acids and flavonoids, which have anti-inflammatory and antioxidant properties and protect tissues from oxidative stress. Flavonoids counteract free radicals, endothelial dysfunction, and platelet aggregation [77]. The intake of legumes four times a week in a nutritional plan against obesity with a moderately low-calorie diet resulted in a decrease in lipid-associated oxidative stress with a decrease in lipid peroxidation biomarkers, such as oxidized LDL and malonylaldehyde, and also in C-reactive protein, independent of weight loss [78].

3. Barriers towards the Consumption of Legumes

3.1. Phychosocial and Socio-Economic Reasons

3.1.1. Food Neophobia Tendencies

3.1.2. Food Taboos

3.1.3. Socio-Economic Factors

3.2. Digestibility and Health-Related Concerns