Don't you love it when you hear how good and healthy fruits/vegetables are for you? How you need fiber and all those good vitamins/minerals which are all lacking in animal foods (check part one to see the actual truth). Let's talk about something that is usually not mentioned, the anti-nutrients present in plants. - ANTINUTRIENTS IN PLANT-BASED FOODS2.1. Lectins
Lectins, particularly abundant in plants, are proteins or glycoproteins of non-immune origin. They have the ability to bind, without modifying, to either carbohydrates or glyco-conjugates (glycoproteins, glycolipids, polysaccharides). They can successfully recognize animal cell carbohydrates, which corresponds to the Latin derivation of the word legere meaning to select [
21]. Lectins have a variety of roles. They can bypass human defense system and travel all over the body causing diseases (
i.e. Crohn’s disease, Coeliac-Sprue, colitis,
etc.) by breaking down the surface of the small intestine [
22]. When large quantities of lectins are introduced in the body, the gut wall develops holes, and intestinal permeability, causing the leaky gut syndrome. Lectins can make cells act as if they have been stimulated by insulin or cause the insulin release by the pancreas. Lectins can also cause autoimmune diseases by presenting wrong immune system codes and stimulating the growth of some white blood cells [
23,
24]. This may possibly lead to cancer but lectins have not yet been recognized as cancer causing.
Not all variety of lectins are toxic or responsible for intestinal damage. Lectins can be found in plant species such as wheat, beans, quinoa, peas,
etc. [
25]. As grains are a common part of the birds’ diet, it has been found that birds themselves are resistant to grains lectins [
26]. Acne, inflammation, migraines or joint pains can be caused by the consumption of lectins [
27]. Lectins are usually found in the hull so choosing white rice can lower the lectin intake. Heating plant sources in the process of cooking can significantly lower the amount of lectins in them. White potatoes, for instance, have a higher lectin content compared to sweet potatoes [
28]. Almonds are also a richer lectin source than peanuts [
29].
2.2. Trypsin Inhibitors
Trypsin inhibitors occur in a wide range of foods like chickpeas, soybeans, red kidney beans, adzuki beans, mung beans and other representatives of the Leguminoseae, Solanaceae, and Gramineae families [
30]. Ten percent of the world’s dietary protein is derived from grain legumes [
31]. Trypsin inhibitors redound to the loss of trypsin and chymo-trypsin in the gut, thus preventing protein digestion. Excess trypsin synthesis and burden on sulfur-containing amino acids in requirement of the body are due to the release of chole-cystokinin triggered by trypsin inhibitors [
32].
2.3. Alpha-amylase Inhibitors
Inhibition of α-amylase is considered a strategy for the treatment of disorders in carbohydrate uptake, by reducing insulin levels, as well as, dental caries and periodontal diseases [
33]. Amylase inhibitors are substances that bind to alpha amylases making them inactive [
34]. Two roles of α-amylase inhibitors have been identified. The primary function of inhibitors is protecting the seed against microorganisms and pests, and the other function is the inhibition of the endogenous α-amylase [
35]. However, the instability of this inhibitor under the conditions of the gastrointestinal tract and being a very heat-liable constituent results in its failure to be used as starch blocker [
36]. It is used to control human diabetes type two [
37] and finds several applications in the food industry [
38,
39].
2.4. Protease Inhibitors
Proteases are key cell-process-regulation enzymes that are found in all cells and tissues. Protease inhibitors are commonly present in raw cereals and legumes, especially soybean. Protease inhibitors bind to their target proteins reversibly or irreversibly. Growth inhibition, pancreatic hypertrophy [
40], and poor food utilization [
41] are associated with protease inhibitors’ antinutrient activity. Exopeptidases remove amino acids from the C- or N-terminus, whereas endopeptidases are capable of cleaving peptides within the molecule [
42]. Grain eating birds have evolved digestive enzymes that are resistant to grain protease inhibitors [
26]. In human volunteers and in animal experiments, high levels of protease inhibitors lead to an increased secretion of digestive enzymes by the pancreas [
43].
2.5. Tannins
Plant tannins are a major group of antioxidant polyphenols found in food and beverages that attracts research interest with its multifunctional properties to human health. Tannins are oligomers of flavan-3-ols and flavan-3, 4-diols that are concentrated in the bran fraction of legumes [
44]. Grapes and green tea are rich in this water-soluble polyphenol [
45]. Tannins exhibit antinutritional properties by impairing the digestion of various nutrients and preventing the body from absorbing beneficial bioavailable substances [
46]. Tannins can also bind and shrink proteins. Tannin-protein complexes may cause digestive enzymes inactivation and protein digestibility reduction caused by protein substrate and ionisable iron interaction [
47].
2.6. Phytates
Phytates occur in several vegetable products. Seeds, grains, nuts and legumes store phosphorus as phytic acid in their husks in the form of phytin or phytate salt. Their presence may affect bioavailability of minerals, solubility, functionality and diges-tibility of proteins and carbohydrates [
41]. Phytic acid is most concentrated in the bran of grains [
48]. In legumes, phytic acid is found in the cotyledon layer and can be removed prior to consumption [
49]. The digestive enzyme phytase can unlocked the phosphorus stored as phytic acid. In the absence of phytase, phytic acid can impede the absorption of other minerals like iron, zinc, magnesium and calcium by binding to them [
50]. This results in highly insoluble salts that are poorly absorbed by the gastrointestinal tract leading to lower bioavailability of minerals. Phytates also inhibit digestive enzymes like pepsin, trypsin and amylase [
51].
2.7. Goitrogens
Hypothyroidism is increasing daily worldwide as the thyroid gland is highly sensitive to stress and environmental stimuli [
52]. Goitrogens interfere with iodine uptake and thus, affect thyroid function. Vegetables from the genus Brassica
i.e. broccoli, cabbage, cauliflower, Brussels sprouts and kale are some of the goitrogen rich foods [
53]. The consumption of cruciferous vegetables affects triiodothyronine (T3) and thy-roxine (T4) levels by causing hypothyroidism [
54]. Concomi-tant factors can be insufficient water consumption and protein malnutrition [
55].
2.8. Raffinose Oligosaccharides
Raffinose, stachyose and verbascose, all part of the Raffinose Family Oligosaccharides (RFOs), are synthesized from sucrose. Non-digestible oligosaccarides have a prebiotic effect in the lower intestine by promoting the growth of
Bifidobacterium and
Lactobacillus that inhibit pathogenic growth [
56]. The absence of appropriate enzyme activity to hydrolyse RFOs (α-galactosidase) leads to the inability of humans and to digest RFOs an allow them to pass through the intestinal wall intact [
51,
57]. A correlation between legumes consumption and the likelihood of intestinal discomfort has been drawn leading to symptoms like burping, abdominal pain, and bloating [
57]. The presence of RFO in the daily food intake can interfere with the digestion nutrients [58]. RFO can reduce metabolizable energy and protein utilization [
59]. Research has shown that RFO removal has improved the digestion of all amino acids increasing the overall nutritional value of the lupin diet [
60].
2.9. Saponins
Some saponins (steroid or triterpene glycoside compounds) can be used for food while others are toxic. Saponins with a bitter taste are toxic in high concentrations and can affect nutrient absorption by inhibiting enzymes (metabolic and digestive) as well as by binding with nutrients such as zinc. Saponins are naturally occurring substances with various biological effects. In the presence of cholesterol, saponins exhibit strong hypocholesterolemic effect [
61]. They can also lead to hypoglycemia [
62] or impair the protein digestion, uptake vitamins and minerals in the gut, as well as lead to the development of a leaky gut [
63].
2.10. Oxalates
Some organic acids can have antinutritional factors. Oxalic acid can form soluble (potassium and sodium) or insoluble (calcium, magnesium, iron) salts or esters called oxalates that are commonly found in plants
i.e. leafy vegetables or syn-thesized in the body [
64]. Insoluble salts cannot be processed out of the urinary tract once processed through the digestive system. Calcium oxalate can have a deleterious effect on human nutrition and health by accumulating kidney stones [
65]. Cruciferous vegetables (kale, radishes, cauliflower, broccoli), as well as chard, spinach, parsley, beets, rhubarb, black pepper, chocolate, nuts, berries (blueberries, black-berries) and beans are some of the foods with high amounts of oxalates [
66]. Most people can induct normal amounts of oxalate rich foods, while people with certain conditions, such as enteric and primary hyperoxaluria, need to lower their oxalate intake. In sensitive people, even small amounts of oxalates can result in burning in the eyes, ears, mouth, and throat; large amounts may cause abdominal pain, muscle weakness, nausea, and diarrhea [
67].
Table
1 is revealing some food sources with the typical antinutrients contained in them as well as the amounts variables.
2.11. Exorphins
The alcohol-soluble proteins (proalimins) of cereal grains and dairy products called gliadins can be further degraded to a collection of opioid-like polypeptides named exorphins in the gastrointestinal tract [
81]. Behavioral traits such as spon-taneous behavior, memory, and pain perception can be affected by the bioactivity of food-derived exorphins [
82]. Exorphins can also influence gastric emptying and intestinal transit by increasing its time [
83]. The digestion of milk produces alpha-casein-derived exorphins [
84]. Recent research suggests that epigenetic effects of milk-derived opiate peptides may contribute to gastrointestinal dysfunction and inflam-mation in sensitive individuals [
85].
Fig. (
1) pinpoints some of the widely speard antinutrients in plant-based foods.
2.12. Contextual Antinutrients
Some supplements or foods rich in certain nutrients can create reactions of an antinutrient nature. For instance, calcium-rich foods can impede iron absorption. There is also a mutual antagonism between zinc and copper during the absorption process, taking place in/on the intestinal epithelium [
86]. Research literature suggests that phytosterols [
87] and phospholipids [
88] may reduce cholesterol absorption when added to nonfat foods. Some foods can interfere with medication absorption [
89]. The most well publicized food-drug interaction is that of grapefruit and a variety of drugs. Bergamottin found in grapefruit juice inactivates drug-metabolizing enzymes. This is the reason why food interaction warnings are listed on some medical labels. Studies have found that resveratrol, found in red wine and peanuts, inhibits platelet aggregation, and high intakes could increase the risk of bleeding when consumed with anticoagulant drugs [
90]. Canadian researchers have documented that black tea was a more powerful enzyme inhibitor than single-ingredient herbal teas (St. John’s Wort, feverfew, cat’s claw,
etc.) [
91]. Another well-known food-drug interaction is that of foods containing tyramine (chocolate, beer, wine, avocados,
etc.) and mono-amine oxidase inhibitors (type of antidepressant) [
92]. The most medically consequential food-drug interaction is that of vitamin K-rich foods (
e.g. broccoli, spinach) and Coumadin, an anticoagulant prescribed to thin the blood and prevent clots [
93].
CONCLUSION
Antinutritional factors are widespread food compounds that are especially challenging for those choosing a predominantly plant-based diet
i.e. vegan, vegetarians,
etc. Antinutrients can exhibit beneficial health effects if present in small amounts or cause nutrient deficiencies. Uninformed consumers may deal with some misleading information when the latter is not sufficiently available. Antinutrients may induce their undesirable effects when consumed above their upper limit. Harmful effects can also be due to antinutritional breakdown products. Thus, the presence of lectins, tannins, alkaloids, and saponins, goitrogens, inhibitors,
etc. in foods may induce various reactions when the consumer is presented with little knowledge related to the environmental influence on the detoxification capacity of the human organism. Classic approaches and modern agricultural biotechnological programs can serve as antinutritional removal tools. However, health risk factors can be avoided when a daily sustainable diet lying on a sound scientific basis is introduced.
Sources There are tons of other sources I could use, you can also search for them yourself. Plenty of evidence on this.