Antinutrients in Food – What to Watch Out for in Your Diet

What Are Antinutrients?

Antinutrients are naturally occurring chemical compounds found in food that can interfere with the absorption or utilization of nutrients by the body.

They are found mainly in plant-based products, where they serve as a natural defense mechanism against pests and pathogens. They function by binding to nutrients such as minerals, proteins, or digestive enzymes, rendering them unavailable to the body. This can lead to reduced absorption of essential macro- and micronutrients.

How Antinutrients Work

Antinutrients can interact with dietary components like iron, copper, calcium, iodine, zinc, and magnesium, thus negatively affecting their absorption. This effect can be reduced through:

• Proper food preparation techniques (soaking, sprouting, rinsing)

• Thermal processing (cooking, baking)

• Appropriate combining or avoiding certain ingredient pairings

Long-term consumption of large quantities of antinutrients can lead to nutrient deficiencies and weakened health. In moderate amounts, however, antinutrients are not harmful. In some cases, they may even offer health benefits, such as antioxidant effects or blood sugar regulation. Their impact depends on the amount consumed, processing methods, and the overall quality of the diet.

Most Common Antinutrients in Food

Below is an overview of the most prevalent antinutrients found in food:

Phytic Acid

Found in: legumes, flours made from legumes, grains, nuts, and seeds. Whole grain products contain significantly more phytic acid than their refined counterparts.

How it works: Phytic acid binds to minerals (iron, zinc, calcium, phosphorus, magnesium, and manganese), forming insoluble complexes that are excreted without being absorbed.

Excessive intake of foods high in phytic acid can lead to mineral deficiencies, especially of zinc and non-heme iron.

How to reduce phytic acid:

• Soaking and sprouting seeds and grains to activate phytase enzymes

• Fermentation, such as sourdough bread preparation

• Milling grains to remove outer layers rich in phytic acid

• Acidifying the environment, e.g., adding vitamin C or apple cider vinegar – 50 mg of vitamin C can counteract phytic acid’s negative effect on iron bioavailability

Oxalates

Rich sources: spinach, rhubarb, sorrel, strawberries, beet greens, cocoa, coffee, tea. Most abundant in stems and lower leaves of plants.

In a typical diet, coffee and tea are the main oxalate sources. Loose-leaf teas contain more oxalates than tea bags. Longer brewing and leaving leaves in the cup increases oxalate content.

The impact of oxalates is strongly influenced by the dietary calcium to oxalate ratio. Moderate oxalate intake (up to 40–50 mg/day) is generally safe.

High oxalate intake, especially with low calcium and vitamin D intake, reduces calcium absorption by forming insoluble calcium oxalate, potentially disrupting calcium-phosphate balance and increasing the risk of kidney stones.

How to reduce oxalate effects:

• Soaking and sprouting

• Thermal processing (boiling, baking), which can reduce oxalate content by up to 50%

• Avoid combining high-oxalate foods with calcium-rich foods

Polyphenols

Found in: vegetables, berries (strawberries, blueberries, raspberries), legumes, whole grains, nuts, and drinks like tea, coffee, and cocoa.

Benefits: Strong antioxidants that neutralize free radicals, reducing the risk of cardiovascular disease and cancer.

Risks: Excessive intake may impair iron absorption. Vegetarians, who rely on non-heme iron, should avoid drinking tea or coffee with meals.

Saponins

Found mainly in: legumes, but also in beets, sweet potatoes, asparagus, oats, potatoes, spinach, and herbs.

Low doses may lower blood cholesterol and glucose levels and have anti-cancer properties.

High intake may cause:

• Hemolysis (destruction of red blood cells)

• Impaired protein digestion and absorption of vitamins and minerals

Saponins are thermostable – they remain in food even after cooking.

Lectins

Found in: legumes (primary source), but also in fruits (bananas, melons, plums, strawberries, apples, grapefruits) and vegetables (onions, leeks, garlic, tomatoes, potatoes).

Effects: Can damage gastrointestinal cells and disturb gut microbiota. Some may stimulate the immune system.

Most lectins are deactivated by cooking, but some are highly heat-resistant. Boiling legumes is the most effective method of reducing lectins.

Protease Inhibitors

These compounds inhibit trypsin and/or chymotrypsin, reducing the digestion of peptides and proteins in the small intestine.

Found in: legumes (soybeans, lentils, beans, broad beans, peas), seeds (sunflower, poppy), and cereals (wheat, rye, buckwheat, barley, oats).

Thermal processing is the most effective way to inactivate them, though the effectiveness depends on factors such as moisture, cooking time, method, and temperature.

Glucosinolates

About 100 different glucosinolates exist in cruciferous vegetables (e.g., cabbage, broccoli, kohlrabi, Brussels sprouts, cauliflower, arugula, radishes). Their concentration depends on plant species, variety, climate, soil, and storage conditions.

Inactive by themselves, they break down into bioactive compounds upon contact with the enzyme myrosinase, released when vegetables are chopped or chewed.

Benefits: Anticancer and antiviral properties.
Risks: May disrupt thyroid, adrenal, pancreatic, liver, and kidney function due to goitrogenic effects (especially with low iodine intake), possibly leading to thyroid enlargement (goiter).

People with normal thyroid function need not worry. However, those consuming large amounts of raw cruciferous vegetables (>500 g/day) should include iodine-rich foods.

Cooking cruciferous vegetables uncovered helps reduce glucosinolate levels as they evaporate with steam.

Tannins

Tannins are plant polyphenols with antioxidant properties, found in:

• Coffee and tea (major sources)

• Berries, grapes, cocoa, apples, legumes

Downside: They form strong complexes with minerals and vitamins A and B12, hindering their absorption.

Tip: Avoid consuming tea or coffee during meals to reduce tannin interference.

Summary Table: Common Antinutrients