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Lectins, present especially in common beans (Phaseolus vulgaris) and peas (Pisum sativum; Table 1), have a negative role in nutrient absorption (by binding intestinal epithelial cells), and in the integrity of the mucosa, causing intestinal hyperplasia and high permeability (Figure 1; Petroski and Minich, 2020; Samtiya et al., 2020), which allow bacteria contact with the bloodstream (Samtiya et al., 2020). Despite lectins are resistant to enzymes in the gastrointestinal tract, they can be reduced/removed by boiling, soaking, autoclaving, fermenting, germinating, and milling (Figure 1; Petroski and Minich, 2020). For example, boiling white and red kidney beans can eliminate lectin content (Nciri et al., 2015). However, lectins may have clinical benefits, for example, some studies show that they can recognize different glycan production of cancer cells and therefore can be potentially used in cancer treatments (Figure 1; Panda et al., 2014; Gautam et al., 2018, 2020; Bhutia et al., 2019; Mullins and Arjmandi, 2021). Besides, they positively activate the immune system, modifying the expression of interleukins and some protein kinases, and have been demonstrated as possible antiviral and antimicrobial agents (Figure 1; Lagarda-Diaz et al., 2017; Mullins and Arjmandi, 2021). For instance, in the treatment of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), responsible for the currently COVID-19 pandemic, lectins can bind complex-type-N-glycans on viral glycoproteins, like coronaviruses spike and prevent the production of viral proteins and the cytopathic effect in host cells (Liu et al., 2020).

Protein and Alpha-amylase inhibitors may present higher activity units in common beans and chickpeas (Cicer arietinum; Table 1) and are natural plant inhibitors that interfere with mineral bioavailability, nutrient absorption, and protein and starch digestibility (Figure 1; Sánchez-Chino et al., 2015; Samtiya et al., 2020). Although studies are limited and not recent and this subject remains controversial, it has been broadly reviewed that some of the inhibitors, like Bowman-Birk, may present anticarcinogenic effects (Figure 1; Muzquiz et al., 2012; Sánchez-Chino et al., 2015; Srikanth and Chen, 2016; Kårlund et al., 2021).


Oxalates are often labeled as deleterious non-nutrients and are frequently present in soybean, fava bean, and peas (Figure 1), but also in non-legumes (Mitchell et al., 2019; Petroski and Minich, 2020). They are usually associated with a reduction in mineral bioavailability and absorption (through chelating minerals) and with favoring kidney stones formation (Shi et al., 2018; Petroski and Minich, 2020). Oxalates are usually excreted in urine (Shi et al., 2018), and its excretion can be promoted via proper hydration, Ca consumption (Ca binds to oxalates during digestion), and vitamin C balance (which may influence the oxalate endogenous production; Mitchell et al., 2019). Boiling, soaking, steaming, and combining with high Ca-rich foods help to reduce oxalate content (Figure 1; Petroski and Minich, 2020). For example, soaking seeds of different legumes species reduced the oxalate content by 17–52% and the reduction even increased after cooking, 31–66% (Shi et al., 2018). Nevertheless, it is necessary to have into account that legumes are not the only oxalate source; cooked and raw spinach is considered the major supplier since ingestion of 50–100 g of spinach (normal portion) provides around 500–1,000 mg of oxalate (Mitchell et al., 2019); also in cocoa powder, oxalates content was found to be 619 mg/100 g; in sweet potatoes 496 mg/100 g and in okra 317 mg/100 g (Siener et al., 2020).


Phytate or phytic acid, a non-proteinaceous non-nutrient (Raes et al., 2014), frequently present in soybeans, fava beans, and common beans (Table 1), can chelate Fe, Zn, and Cu, and can negatively affect their absorption in the gastrointestinal tract (Figure 1; Samtiya et al., 2020). People that consume a large amount of legume grains as a part of their diet can have lower levels of Fe. In extreme cases, this can cause anemia (Shi et al., 2018), if the recommended daily doses are exceeded or it is not maintained a balanced diet. The adequate provision of vitamin C in the diet is a good option to counteract these negative effects since it keeps Fe available for absorption (Bohn et al., 2008; Petroski and Minich, 2020). Nevertheless, phytates have important health benefits, such as anticarcinogenic properties and antioxidant activity (Figure 1), chelating toxic metals, palladium and cadmium, or excess Fe, thus preventing harmful Fenton reactions (Shi et al., 2018; Petroski and Minich, 2020).


Phenolic compounds, present in Canavalia spp. and cowpea (Vigna unguiculata; Table 1), can have anti-inflammatory and antioxidant properties, improve gut health (Filosa et al., 2018), lead to the inhibition of glucose regulation enzymes a-amylase and amyloglucosidase (Sánchez-Chino et al., 2015), and reduce the risk of CVD, type 2 diabetes, metabolic syndrome, ischemic stroke, and atherosclerotic vascular disease (Petroski and Minich, 2020). Nevertheless, not all polyphenolic compounds have health benefits, for example, tannins. Found mostly in the outer layers of grains and seed coats and, in higher concentration, in fava beans (Table 1), but also in cocoa beans, tea, wine, and fruits, they have the capacity of interfering with Fe absorption and storage, contributing to Fe deficiency anemia


Phytoestrogens, present especially in soy products (tofu, tempeh, and soymilk), have a similar structure to the female primary sex hormone, 17-ß-estradiol, and also have some health concerns; they may be involved in endocrine disruption and increase the risk of estrogen-sensitive cancers (Figure 1; Petroski and Minich, 2020). However, there are some references to anticarcinogenic effects (Figure 1; Sánchez-Chino et al., 2015; Petroski and Minich, 2020). These compounds can be reduced through boiling, fermenting, and steaming (Figure 1; Petroski and Minich, 2020).


Saponins in plant foods can interact with erythrocytes increasing the risk of hemolysis, inhibit digestive enzyme activities causing indigestibility disorders, and reduce vitamin absorption (Figure 1; Samtiya et al., 2020). However, saponins can also reduce the risk of CVD, cancer, blood cholesterol, and blood glucose; increase bile acids excretion, cell proliferation regulation, and have anti-inflammatory and immune-stimulatory activities (Figure 1; Sánchez-Chino et al., 2015; Singh et al., 2017).


Since the consumption of non-nutrients has contrasting health effects, the possibility of reducing or increasing their content in different legumes has been considered (Gutierrez et al., 2008; Cominelli et al., 2018; Khazaei et al., 2019). The vast majority can be reduced or even eliminated by traditional food preparation procedures (Figure 1), and proper processing methods can reduce their amount and increase the protein digestibility and biological value of legumes (Samtiya et al., 2020).