April 2024 Issue

CPE Monthly: Antinutrients in Foods
By Mary Franz, MS, RDN, LDN
Today’s Dietitian
Vol. 26 No. 4 P. 28

Learn about their impact on human health and strategies to reduce consumption.

Take this course and earn 2 CEUs on our Continuing Education Learning Library

Antinutrients are naturally occurring biological substances that provide plants with protection against harmful viruses, bacteria, and insects. These biological substances are termed “antinutrients” because they exert potentially detrimental effects on the bioavailability of essential nutrients.1 Although plant-based diets are rich in valuable micronutrients and antioxidants, they also contain high levels of antinutrients, which may interfere with digestion, absorption, and metabolic processes. Conversely, some antinutrients in plant foods also may be beneficial and provide anticarcinogenic, antioxidant, detoxifying, and cardioprotective effects.2

This continuing education course explores the diverse effects antinutrients in plant foods may have on health. Evidence demonstrating the favorable and undesirable effects of individual antinutrients is presented. Strategies for minimizing potentially detrimental levels of antinutrients in foods also is discussed.

Types of Antinutrients
Antinutrients have been identified in grains, legumes, nuts, seeds, fruits, and vegetables. The most important of these include lectins, phytate, oxalates, tannins, saponins, glucosinolates, and enzyme inhibitors. The amounts of antinutrients in plant foods may vary greatly with the species of plant and type of cultivar, growing conditions, type of processing, and cooking method.1 Moreover, plant foods are complex matrixes of many interacting nutrients that may influence the activity and effects of antinutrients.1

Lectins are glycoproteins found primarily in legumes and, to a lesser degree, in quinoa, peppers, potatoes, and tomatoes. Lectins are classified as hemagglutinins because they bind to receptors on red blood cells, causing them to clump. Plant lectins have been shown to cause in-vitro agglutination of human red blood cells.1,3,4 The hemagglutination capacity of a substance is expressed in terms of hemagglutinin units (HAUs). One HAU is defined as the “minimum amount of a substance that will cause complete agglutination of red blood cells.”5

Because lectins are resistant to digestive enzymes, they linger in the small intestine, where they bind to epithelial membrane glycoproteins.3 The resulting increase in intestinal permeability can trigger inflammation and has been associated with increased risk of gastrointestinal diseases such as Crohn’s disease, celiac disease, and leaky gut syndrome.6 Although most ingested lectins bind to the gut mucosa, some lectins may be carried across the intestinal mucosa into the bloodstream. Once they’ve entered the circulation, lectins bind to receptor cells in the liver, pancreas, and bladder, triggering immune responses that may precipitate the onset of chronic diseases, notably rheumatoid arthritis.7

Lectin levels are highest in raw legumes, with some of the greatest concentrations found in raw lima beans (26,526 HAU/g), raw black beans (26,429 HAU/g), raw kidney beans (13,214 HAU/g), raw soybeans (3,328 HAU/g), and raw peas (414 HAU/g).3

Consumption of raw legumes can cause acute food poisoning with nausea, diarrhea, and vomiting.3 These gastrointestinal symptoms appear to be related to intestinal inflammation and microvillar damage resulting from exposure to lectins rather than the accumulation of lectins in the bloodstream.8 Between 2004 and 2013, around 7,000 people in China were sickened by eating raw or undercooked kidney beans.1 Other cases of lectin poisoning resulting from the consumption of raw legumes have been reported in the United Kingdom, Japan, and Denmark.3 Although a standard for a safe level of consumption of lectins hasn’t been established, a range of 400 to 3,200 HUA has been proposed to be potentially toxic.3

Guidelines for preparing legumes to reduce the risk of illness resulting from ingestion of lectins have been established by the World Health Organization, which recommends that dried legumes be soaked for 12 hours and then boiled for a minimum of 10 minutes. The FDA recommends five hours of soaking followed by 30 minutes of cooking. Adherence to these recommendations was reported to result in complete destruction of lectins in legumes.3

In addition to their toxicity, some plant lectins may provide beneficial effects in combating disease. Lectins derived from wheat germ and tepary beans have been found to inactivate leukemia and colon cancer cells and may show promise as adjuvant chemotherapeutic regimens.9 Complete remission of colon cancer was observed in a patient who received injections of a lectin extracted from the mistletoe plant; in addition, 50 patients with stage IV nonsmall cell lung cancer experienced longer survival rates when they received mistletoe lectin in conjunction with standard chemotherapy.10,11

Phytate, known also as IP6 or phytic acid, is a storage form of phosphorus found primarily in cereal grains, legumes, nuts, and seeds. Phytate consists of the sugar inositol bound to six phosphate groups, which act as mineral chelators.1

Levels of phytate are highest in unprocessed grains in which the bran layers are intact. Rich food sources of phytate include wheat bran (1,000 to 2,200 mg/100 g), legumes (386 to 714 mg/100 g), nuts (150 to 9,400 mg/100 g), grains (50 to 74 mg/g), and pseudo-grains, such as quinoa, amaranth, and buckwheat (0.5 to 7.3 g/100 g).6,12

Because dietary phytate can’t be digested by humans, it can bind to zinc, iron, and calcium in the gut and decrease their bioavailability.1 High intakes of phytate have been associated with iron and zinc deficiencies.13 Phytate exhibits a dose-dependent inhibitory response on zinc and iron bioavailability.13

Daily phytate intakes have been estimated to be 2,000 to 2,600 mg among vegetarians and individuals in rural, developing countries, whereas mixed Western-type diets may provide as little as 650 mg of phytate per day.1

The phytate to zinc molar ratio often is calculated to assess the effect of the phytate amount in a food on the absorption of zinc from the food using the following equation14:

Phytate (mg/660) / Zinc (mg/65.4)

Molar phytate to zinc ratios of 5 or more have been associated with substantial decreases in zinc absorption.14 Higher phytate to zinc ratios are observed in populations consuming unrefined and unprocessed grains.13 Gibson and colleagues reported findings from a meta-analysis of 30 multinational clinical trials that investigated the effect of phytate intake on zinc absorption among adults aged 18 to 79. Test diets with phytate to zinc molar ratios greater than 15 were associated with a 45% lower zinc absorption compared with control diets with phytate to zinc ratios less than 15.13

In addition, a review of nutrition surveys conducted in 25 low- and middle-income countries among adult men and women aged 15 to 60 and male and female children aged 6 months to 14 years demonstrated that zinc deficiency, as assessed by plasma/zinc serum concentrations, was significantly associated with molar phytate to zinc ratios.15

Similarly, a molar phytate to iron ratio may be calculated to determine the effect of increasing phytate consumption on iron absorption using the following equation16:

[Intake of phytate (mg/day)/660] / [Intake of iron (mg/day)/56]

Phytate appears to have a more detrimental effect on iron bioavailability, compared with zinc. Accordingly, a phytate to iron ratio greater than 1:1 has been shown to decrease iron bioavailability, whereas a ratio of 0.4:1 or less may best promote iron absorption, particularly for diets rich in grains and legumes.13

Although high levels of phytate are known to inhibit iron absorption, associations between phytate to iron molar ratios and iron status are less clear. A study of women aged 15 to 49 and children aged 6 to 14 from a national survey conducted in Bangladesh demonstrated that molar phytate-to-iron ratios of 5.47 to 6.12 weren’t associated with iron-deficiency anemia, as evidenced by hemoglobin concentrations of 12.5 to 12.6 g/dL. The authors note that other factors, such as the iron content of drinking water, may modify the effects of high phytate intakes on iron absorption.16

The effect of phytate on calcium absorption isn’t well understood. Because the threshold at which phytate interferes with calcium bioavailability hasn’t been identified, molar phytate to calcium ratios are seldom used to assess calcium absorption. In addition, calcium deficiency appears to be more strongly related to low dietary calcium rather than the inhibitory effects of phytate.13

Vitamin C and probiotics have been shown to offset the inhibitory effect of phytate on mineral absorption in the gut.1 Banerjee and colleagues cite studies that reported a lessening of the phytic acid load of meals in response to vitamin C supplementation of 50 to 80 mg.17 The lactic acid bacteria found in many probiotics produce phytases, which degrade phytate, thereby increasing the bioavailability of iron, calcium, and zinc.18

Phytate also may provide some beneficial effects. Phytate can bind excess iron that acts as a catalyst in oxidation reactions in which free radicals are formed. A randomized clinical trial conducted among 33 adult subjects with type 2 diabetes found that daily supplementation with 1 g of phytate reduced the production of advanced glycation end-products, biomarkers associated with oxidative stress and inflammation.19 Phytate also may reduce the absorption of iron in patients with hemochromatosis, a genetic disease that causes the body to absorb too much iron from food, often leading to dangerously high levels of iron to accumulate in the body.20 In addition, preliminary research shows that phytate may lower the risk of osteoporosis. The phosphorus content of phytate may protect against bone loss by reducing the activity of osteoclasts and preventing the dissolution of hydroxyapatite, a form of calcium found in the body that contributes to bone strength.1,21

Oxalate is a salt consisting of oxalic acid bound to a mineral. Oxalate exists in plants in either soluble or insoluble form. Soluble oxalate is formed when oxalic acid binds to sodium or potassium, while insoluble oxalate is composed of oxalic acid joined to calcium, iron, or magnesium.22 Oxalates obtained from the diet can promote hyperoxaluria, a risk factor for the formation of kidney stones. Although most insoluble oxalates are excreted intact in the feces, crystals of calcium oxalate can accumulate in the renal glomeruli and can lead to the formation of kidney stones.23,24 Oxalate also may be produced endogenously.1 Urinary oxalate consists of about 50% dietary oxalate and 50% endogenous oxalate.25

Foods with high levels of oxalate include spinach, beets, Swiss chard, sweet potatoes, amaranth, legumes, cocoa, grains, and nuts. Because soluble oxalate may play a role in kidney stone formation, both the total and soluble oxalate content of a food are of interest. On average, fresh spinach contains 978 to 1,145 mg/100 g of total oxalate and 543 to 803 mg/100 g of soluble oxalate. The mean total oxalate contents of cocoa, sweet potatoes, and kidney beans were found to be 619, 496, and 75 mg/100 g, respectively, whereas the mean soluble oxalate content of these foods was determined to be 571, 77, and 5 mg/100 g, respectively.26

Despite long-standing acceptance of the causal role of oxalate in kidney stone formation,23 recent studies demonstrate an inconsistent relationship between dietary oxalate and kidney stone occurrence. The Nurses’ Health Study found that the highest intakes of oxalate were only marginally associated with the risk of developing kidney stones, whereas individuals with the lowest intakes of calcium carried a higher relative risk of kidney stone formation (1.46) compared with the highest intakes of oxalate (RR = 1.21).1 Similarly, Mitchell and colleagues found that among 39 male and female adults aged 22 to 43, low intakes of calcium (400 mg/day) increased urinary excretion of oxalate by as much as 50%, raising the risk of kidney stone formation.25

Moreover, despite the DASH diet’s relatively high content of foods rich in oxalates as well as phytate, it appears to be associated with a 40% to 50% lower risk of kidney stones, compared with typical Western-style diets. This effect may be due to the interactive effect of phytochemicals, vitamins, and minerals present in foods consumed on a DASH-style diet.1

Tannins are high molecular weight polyphenols found in a wide variety of plant foods. Tannins are responsible for the familiar astringent taste of tea, fruits, and vegetables. Two groups of tannins have been identified in foods: condensed tannins and hydrolysable tannins. Condensed tannins include catechins, which are the most common types of tannins found in foods. Major food sources of catechins include black grapes (204 mg/kg), berries (11 to 188 mg/kg), apples (71 to 115 mg/kg), red wine (27 to 96 mg/L), green tea (100 to 800 mg/L), and black tea (60 to 500 mg/L).1,9 Hydrolysable tannins include ellagitannins, found in berries, pomegranates, and walnuts, and gallotannins, found in mangoes and almonds.9,27

Tannins in tea have been shown to bind iron in the small intestine and have been associated with reduced serum hemoglobin levels. A study of 400 pregnant women in Pakistan found that women who drank three or more cups of black tea per day had a significantly increased risk of iron deficiency anemia (defined as hemoglobin < 11 mg/dL), compared with women who didn’t drink tea. In addition, serum iron and ferritin levels were significantly higher in non-tea-drinking women.28 Tannins in green tea also may inhibit iron absorption and have been linked to poor iron status in adults.1,29

The effect of tea on iron absorption appears to be strongest for nonheme iron and also may be affected by the interval between food and tea consumption. When tea was consumed with iron-fortified porridge, as revealed by a small cohort (n=12) of nonanemic adult female subjects, nonheme iron absorption decreased by 37%; however, no effect on iron absorption was observed when the subjects consumed tea one hour after the meal.1

The effects of tannins in tea on iron absorption also may vary with sex and iron status. A study investigating the effects of drinking one liter of black tea daily for four weeks among 34 subjects found reduced serum ferritin levels in females, but not males. Both green and black tea consumption lowered ferritin levels in females with low baseline ferritin.1

Tannins also may affect gut health. Because iron is an essential nutrient for many gut bacteria, the ability of tannins to bind iron can therefore lead to disturbances in gut flora and result in detrimental changes in the microbiome.1,30 Tannins also have a strong affinity for binding to proteins and may inactivate digestive enzymes, leading to decreased protein absorption in the digestive tract.9,31

Conversely, tannins also may exert favorable effects on the bacterial composition of the microbiome. Tannins in pomegranate extract stimulated the growth of favorable gut bacteria, specifically Enterococcus, Bifidobacterium spp., and Lactobacillus, in an in vitro study.32,33 The diverse effects of tannins on the microbiome are attributed to fluctuations in bacterial activity within the gut, the interaction of other nutrients present in foods, and the variation in gut bacterial composition among individuals.1,30

Saponins derive their name from the Latin word “sapo” (soap) due to their capacity to form soaplike foams when mixed with water. Saponins are large metabolites of steroid or triterpenoid aglycone molecules that are attached to one or more sugar chains. Food sources of steroid saponins include eggplant (58 g/kg), peanuts (16 g/kg), soybeans (6.5 g/kg), kidney beans (3.5 g/kg), chickpeas (2.3 g/kg), and oats (1.3 g/kg), whereas triterpenoid saponins are found in legumes and quinoa.9,34 The triterpenoid saponin content of kidney beans and green beans has been estimated to be 16 g/kg and 13 g/kg of dry weight, respectively.35 Raw quinoa is a major source of triterpenoid saponins (1.5% to 2% by weight); however, milling and processing of the hulls remove as much as 85% of the saponin content.35

Saponins are toxic compounds that can destroy red blood cells. In vitro studies have demonstrated that some saponins with complex sugar chains may cause hemolytic damage to animal cells. However, evidence supporting the toxicity of saponins to human red blood cells is lacking.36 Moreover, because of their large size, dietary saponins are poorly absorbed by the body and are readily degraded by gut bacteria.34,37

In contrast to the potential toxicity of saponins, some saponins show promise as pharmacological agents. Saponin extracts from the herb Dioscorea nipponica Makino have been shown to reduce LDL cholesterol levels and increase HDL cholesterol concentrations in laboratory rats.38 Ginseng, which contains several types of triterpenoid saponins that comprise 2% of the total weight of the plant, has been shown to provide anti-inflammatory, cardioprotective, antidiabetic, and anticarcinogenic effects in animal and in vitro studies.34,39 Like saponins in foods, the saponins in ginseng aren’t readily absorbed by the body. Instead, they’re metabolized by gut bacteria to form glycosides, which are responsible for ginseng’s therapeutic effects.39

Glucosinolates are sulfur-containing organic compounds that are formed by the metabolism of glucose and amino acids. About 137 glucosinolates have been identified in plants, most of them in the botanical family Brassicaceae. Vegetables in the Brassicaceae family (formerly termed cruciferous vegetables) such as cabbage, broccoli, kale, mustard and turnip greens, cauliflower, Brussels sprouts, and radishes are major dietary sources of glucosinolates.40

Glucosinolates commonly found in Brassicaceae vegetables include glucoraphanin, sinigrin, gluconapin, glucobrassicin, gluconapin, glucoerucin, and glucoiberin.40 Glucosinolates in foods are degraded by gut microflora to form nitriles, isothiocyanates, and sulforaphane, which are then metabolized to goitrin and thiocyanate. Both goitrin and thiocyanate interfere with the uptake of iodine by the thyroid gland and block the action of the enzyme thyroid peroxidase, which regulates the synthesis of the thyroid hormones T3 (thyroxine) and T4 (triiodothyronine). Reduced production of these hormones is associated with increased risk of thyroid diseases, such as goiter and hypothyroidism. Thiocyanate can cross the placenta and cause neonatal hypothyroidism.1,41

The glucosinolate content of Brassicaceae vegetables is highly variable, ranging from 11 to 296 µmol/100 g. Consumption of an average serving size of Brassicaceae vegetables (100 to 200 g) doesn’t appear to adversely affect thyroid function among adults with adequate iodine intake (150 mcg/day).41,42 However, severe iodine deficiency (intake of less than 10 to 20 mcg/day) or overconsumption of Brassicaceae vegetables (more than 1 kg/day) can lead to hypothyroidism.41

Glucosinolates also may exhibit beneficial biological effects. In 2021, Marino and colleagues published a review of 87 clinical trials investigating the effects of glucosinolates on health status among approximately 550 male and female participants aged 18 to 68 in nine countries. Approximately one-half of the subjects were healthy, while 50% experienced poor health status, such as obesity, hypertension, or type 2 diabetes. Twenty-seven of the trials examined the effects of glucosinolate-rich foods, primarily broccoli, broccoli sprouts, Brussels sprouts, kale, and mustard greens, whereas 60 of the studies evaluated glucosinolate extracts derived from Brassicaceae vegetables. The food most often studied was fresh or dried broccoli, consumed in doses of 30 to 400 g daily or several times per week for up to 10 weeks. Findings from this review were mixed. Decreased levels of the inflammatory markers interleukin-6 and C-reactive protein were noted among smokers and overweight subjects after daily consumption of 30 g of broccoli sprouts for 10 weeks. In addition, supplementation with 200 µmols of broccoli sprout extract for four weeks was associated with a decrease in oncogenic biomarkers in the prostate tissue of male subjects. However, beneficial effects of glucosinolate intake on cancer risk, cardiovascular risk factors, cognitive function, and the gut microbiome weren’t consistently observed, suggesting that further investigation of the effects of glucosinolates on health indices is needed.43

Enzyme Inhibitors
Enzyme inhibitors are proteins that inactivate digestive enzymes in the gastrointestinal tract, primarily the proteases, lipases, and amylases. The most nutritionally significant of these are the protease inhibitors, which bind the enzymes trypsin, chymotrypsin, and pepsin in the gut and interfere with protein digestion and metabolism. Protease inhibitors are found in a wide variety of plant foods, including wheat, barley, rice, soybeans, chickpeas, peas, and lentils, and may have the capacity to bind one or more digestive enzymes. A common protease inhibitor found in foods is the Bowman-Birk inhibitor.9,44

Protease inhibitors have been linked with decreased protein absorption and impaired growth and development in children.9 In addition, inactivation of proteases by protease inhibitors in foods has been associated with increased risk of gastrointestinal hypersensitivity, inflammatory bowel disease, and inflammatory bowel syndrome.45 Protease inhibitors in foods also have been linked to pancreatic hypertrophy.6,46

Some protease inhibitors appear to demonstrate favorable effects in the prevention or management of disease. A supplement containing Bowman-Birk inhibitor extracted from soybeans was found to lessen gastrointestinal symptoms in a small clinical trial of adult patients with ulcerative colitis.46

Unlike protease inhibitors, alpha-amylase and lipase inhibitors appear to have few detrimental effects on human health and may have the potential to dampen the effects of risk factors associated with chronic diseases. Alpha-amylase inhibitors are found in a variety of grains (wheat, barley, rice, corn, and rye) and pseudocereals such as quinoa and buckwheat. Extracts of alpha-amylase inhibitors isolated from cereal grains have been shown to block carbohydrate digestion in the gut and prevent hyperglycemia.47 Lipase inhibitors derived from tea, chickpeas, ginger, apples, and peppers may decrease the activity of lipase in the gut.48 Supplementation with lipase inhibitors extracted from foods led to significant improvements in obesity as well as plasma and triglyceride levels in animal studies and human clinical trials.48

Effects of Processing and Cooking on Antinutrients
Industrial food processors use a variety of techniques to reduce levels of antinutrients in foods. Dehulling involves removing the seed coat and husk from seeds and beans and results in lower levels of tannins, phytate, and enzyme inhibitors in legumes and grains.49,50 High temperature heat processing methods such as autoclaving, extrusion, and canning markedly decrease amounts of tannins, phytate, saponins, HAU, and trypsin inhibitors in legumes, grains, and tomatoes.49-51 Endogenous enzymes released during industrial germination of legumes and grains hydrolyze and inactivate lectins, phytate, oxalate, enzyme inhibitors, and phytate.49,52,53 Cereal processors use bacterial fermentation to reduce levels of antinutrients and improve bioavailability of vitamins and minerals in grains.18

Home processing and cooking methods also can significantly reduce levels of antinutrients in foods. Peeling fruits and vegetables can lower their tannin content.1 Legumes often are soaked in water to soften them before cooking. Soaking also leaches phytate, tannins, lectins, oxalates, and saponins from legumes, although the effectiveness of soaking varies with the type of food and antinutrient, as well as the soaking method used.54 Shi and colleagues found that soaking peas, chickpeas, lentils, fava beans, and common beans in distilled water for four hours reduced lectin levels, total oxalate, soluble oxalate, and enzyme inhibitors by 0.11% to 5.2%, 17.4% to 52%, 27% to 56.%, and 4% to 10%, respectively. No effect was noted for phytate.55,56 However, a 20% decrease in phytate was noted in pigeon peas soaked for 18 hours in a mixture of distilled water and salt.57 Soaking for 12 hours was found to reduce saponins in kidney beans by 11%.58 In general, longer soaking times and the addition of salt to soaking water are associated with greater leaching of antinutrients from foods.54,58

Soaking followed by cooking appears to be a more effective means of reducing antinutrients in foods than soaking alone. Lectins were reduced to nondetectable levels when lentils, chickpeas, kidney beans, black beans, and lima beans were soaked for 12 hours in water and then boiled for 30 to 45 minutes. Longer cooking times were associated with a more complete inactivation of lectins in these foods. Similarly, soaking for 12 hours followed by boiling for a minimum of 30 minutes can result in reductions of 50% to 100% in tannins, phytate, saponins, and oxalates in kidney beans and soybeans.1,10,58,59

Boiling is one of the most effective methods for reducing or removing antinutrients from foods. Glucosinolates in broccoli were reduced by 51% by boiling for five minutes, and a 30% to 90% loss of soluble oxalates was observed in vegetables boiled for 12 minutes.10 Boiling legumes for one hour resulted in an 11% to 80% reduction in their phytate content.10 Popova and Mihaylova reported that cooking vegetables for a minimum of 15 minutes at a temperature of 90˚ C could reduce levels of tannins, total and soluble oxalate, and phytate by as much as 50%.6 Finally, levels of chymotrypsin, trypsin, and alpha-amylase inhibitors in peas, lentils, chickpeas, and soybeans were reduced by as much as 90% or completely inactivated by boiling for one hour.56

Steaming is another effective method. Steaming at 98˚ C for 15 minutes reduced levels of oxalates, tannins, and phytate in cabbage by 10% to 90% and decreased oxalates in spinach and Swiss chard by 42% to 46%.1,60 Levels of glucosinolates were reduced by 50% in broccoli steamed for five minutes.1 In addition, steaming for 15 minutes following soaking and dehulling reduced levels of tannins and phytate in common beans by 30% to 40%.61

Microwave cooking also is an effective means of reducing concentrations of some antinutrients in vegetables. Kale, spinach, carrots, tomatoes, beans, and cabbage microwaved for one to five minutes showed reductions of 50% to 100% in levels of tannins, oxalates, phytate, and saponins.60,62 Lectins, however, aren’t inactivated by microwave cooking.1

Studies examining the effects of stir-frying on antinutrients in vegetables have produced inconsistent results. Managa and colleagues found that stir-frying at 125˚ to 140˚ C for one to two minutes reduced levels of oxalates, tannins, and phytate in cabbage by 30% to 90%.60 However, Lo and colleagues reported that stir-frying didn’t significantly reduce levels of phytate in spinach or glucosinolates in Brassica vegetables, noting that temperatures reached during stir-frying may not be high enough to inactivate these antinutrients.62

Dry cooking methods that don’t use water, such as baking, roasting, and grilling, appear to have a lesser effect on inactivating or decreasing levels of antinutrients in foods.63,64 In addition, higher levels of some antinutrients, such as lectins and oxalates, have been reported in roasted and baked foods.1

Putting It Into Practice
Antinutrients in foods influence nutrient absorption, digestion, and metabolism, and can have both positive and negative effects on health and nutrition status. Nutrition concerns such as iron deficiency anemia, protein deficiency in children, thyroid function, and the risk of kidney stone formation may be exacerbated by excessive consumption of dietary antinutrients. Vulnerable individuals should be informed of these possible detrimental effects as well as the potential role of antinutrients on iron and zinc absorption, protein status, and chronic disease risk. Conversely, moderate consumption of some antinutrients, particularly phytate, tannins, saponins, and glucosinolates, may provide anticarcinogenic and cardioprotective benefits.

Nutrition professionals should assess the patients’ diets for types and amounts of antinutrients and educate on the potential risks and benefits of dietary antinutrients in foods frequently consumed. Strategies for mitigating the negative effects of antinutrients, such as adequate vitamin C consumption and use of probiotics, could be considered. Dietary education also should focus on cooking methods that will reduce antinutrient toxicity, promote absorption of vital nutrients, and enhance overall health.

— Mary Franz, MS, RDN, LDN, is a freelance health and science writer based in Norwood, Massachusetts.


Learning Objectives
After completing this continuing education course, nutrition professionals should be better able to:
1. Describe the ways in which antinutrients affect the nutritional quality of plant foods.
2. Evaluate the favorable and unfavorable effects of antinutrients on health.
3. Provide dietary guidance about antinutrients to clients based on individual needs.


1. Phytate has the most detrimental effect on absorption of which of the following nutrients?
a. Calcium
b. Zinc
c. Iron
d. Phosphorus

2. Kidney stone formation may be most strongly influenced by which of the following?
a. Low intakes of calcium
b. High intakes of foods rich in oxalates
c. Adherence to the DASH diet
d. A low phytate to zinc ratio

3. Thiocyanate may cross the placenta and cause neonatal hypothyroidism. Which antinutrient is metabolized to form thiocyanate?
a. Lectin
b. Catechin
c. Tannin
d. Glucosinolate

4. The anti-inflammatory effects of the ginseng plant may be due to which of the following compounds?
a. Amylase inhibitor
b. Saponin
c. Gallotannin
d. Glucoraphanin

5. What level of hemagglutinin units in foods may be potentially toxic?
a. 20 to 50
b. 100 to 200
c. 250 to 350
d. 400 to 3,200

6. What is a possible beneficial effect of protease inhibitors?
a. Decreased insulin resistance
b. Lowered incidence of hypertension
c. Improvements in gastrointestinal symptoms in patients with ulcerative colitis
d. Increased calcium absorption

7. Soaking kidney beans overnight in water may result in which of the following?
a. Complete removal of triterpenoids
b. Increased levels of soluble oxalate
c. Reduced levels of phytate
d. Increased bioavailability of magnesium

8. What is the FDA cooking recommendation for reducing levels of lectins in legumes?
a. Five hours of soaking followed by 30 minutes of cooking
b. Twelve hours of soaking followed by 10 minutes of boiling
c. No soaking and two hours of boiling
d. Three hours of soaking followed by 15 minutes of microwaving

9. Which type of antinutrient has been used as a complementary chemotherapeutic agent in the treatment of stage IV nonsmall cell lung cancer?
a. Glucosinolate
b. Tannin
c. Saponin
d. Lectin

10. A randomized clinical trial found that daily supplementation with 1 g of phytate had which of the following effects?
a. Decreased levels of C-reactive protein
b. Decreased production of advanced glycation end-products
c. Decreased activity of alpha-amylase inhibitor
d. Decreased synthesis of thyroxine


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