what are lectins

Lectins are naturally occurring plant proteins that have been linked to both positive and negative effects.

When taken in small amounts, they are known to help in the immune function and cell growth.

High lectin intake can lead to inflammation and prevent nutrient absorption.

Beans, peanuts, lentils, tomatoes, potatoes, eggplants, fruits, and wheat are some of the foods that contain high amounts of lectins.

Let us learn more about lectins and ways to reduce their adverse effects on the foods that we eat.

What are lectins?

Lectins are naturally occurring carbohydrate-binding proteins found in most plants, especially seeds and tubers like cereals, potatoes, and beans.

These proteins resist being broken down in the gut and are stable in the acidic environment.

This property of lectins helps protect plants in nature (1). Lectins also contain nitrogen, which is needed by the plant for growth.

When eaten in their raw form, lectins can harm you. Raw or undercooked kidney beans contain phytohaemagglutinin, a lectin that causes red blood cells to cluster together.

It can also lead to stomach upset, diarrhea, vomiting, nausea, bloating, and gas.

Lectins are also known as antinutrients as they can block the absorption of certain nutrients.

Studies have found that lectins can interfere with the absorption of calcium, iron, phosphorus, and zinc.

Lectins bind to the cell lining of the digestive tract and disrupt the breakdown and absorption of nutrients, which affects the growth and action of the intestinal flora.

Some studies have also linked lectins to inflammatory conditions like rheumatoid arthritis and type 1 diabetes (2).

While lectins can cause several health issues, they also have some positive effects. Lectins can help in immune function and cell growth.

They also help the good bacteria in the digestive system. Research shows that lectins may also have a potential role in cancer therapy (3).

Scientists are even researching the role of lectins in treatment for illnesses caused by viruses, bacteria, and fungi.

Foods high in lectins

Interestingly most foods that are high in lectin are usually recommended as a part of a healthy well-balanced diet.

These foods are high in nutrients and provide a range of health benefits, that outweigh the harmful effects of lectins.

Also, lectins are most active in their raw state, and most foods that contain them are typically not eaten raw. Let us read about some of the foods that are high in lectins.

1. Red kidney beans

Red kidney beans contain high amounts of a lectin called phytohaemagglutinin, which can cause stomach upset, diarrhea, vomiting, nausea, bloating, and gas.

Raw red kidney beans contain 20,000 to 70,000 lectin units, while cooked red kidney beans contain between 200 to 400 units (4).

This shows that cooking kidney beans can reduce the leptin content to safe levels.

Kidney beans are rich in protein. They are rich in fiber and resistant starch, which helps in weight management (5).

Red kidney beans are also a rich source of many vitamins and minerals like folate, iron, copper, manganese, potassium, and vitamin K1.

2. Soybeans

Soybeans contain high amounts of lectins called soybean agglutinins (SBA). Soybean agglutinins bind to intestinal epithelial cells and cause inflammation and intestinal permeability.

According to a study from the National Key Laboratory of Animal Nutrition, China Agricultural University, consumption of SBA can lead to depletion of lipid and overgrowth in small intestine and pancreas in rats.

It can also cause weak growth of spleen and kidneys in rats (6).

Research has shown that cooking soybeans at 100 degrees for 10 minutes can eliminate lectins. Fermenting soybeans can also lower their lectin content (7).

Soybeans are considered one of the best sources of plant-based proteins. They contain vitamin K, riboflavin, folate, vitamin B6, vitamin C, thiamine, iron, magnesium, phosphorus, copper, potassium, magnesium, zinc, selenium, and calcium.

They also contain isoflavones that help improve bone mineral density (8).

3. Wheat

Wheat, especially wheat germ, contains a lectin called wheat germ agglutinin (WGA).

Animal studies have shown that WGA can cause hyperplastic and hypertrophic growth of the small intestine, hypertrophic growth of the pancreas and thymus atrophy (9).

Raw wheat contains around 300 mcg of wheat lectins per gram. Wheat flour has lower lectin content, and it contains approximately 30 mcg per gram (10).

These figures show that the lectin content of wheat is lowered when it is processed.

Cooking also lowers the lectin content of wheat (11).

Whole wheat contains complex carbohydrates and fiber, which are great for digestive health.

Whole wheat is also rich in plant lignans enterolactone, that is known to protect against heart disease.

Wheat germ is packed with folate, thiamine, vitamin B6, zinc, magnesium, and manganese.

4. Potatoes

The lectins in potato tubers are known as Solanum tuberosum agglutinin (12). This lectin is highly resistant to heat.

Almost 50 percent of the lectin content in potatoes remains intact even after cooking (13).

According to a 2007 study from India, potato lectins can have adverse effects on some people (14).

Potatoes are rich in vitamins, minerals, fiber, and phytochemicals, which can help prevent several diseases.

They are rich in iron, phosphorus, calcium, magnesium, and zinc, which help to keep bones healthy and active.

The high potassium, vitamin C, vitamin B6, and fiber content, along with a lack of cholesterol, also supports heart health.

5. Peanuts

Peanuts contain a lectin known as Peanut agglutinin (PNA), which is also referred to as Arachis hypogaea lectin.

Studies have shown that PNA, which accounts for .15 % of the weight of the peanut, is highly resistant to cooking and rapidly enters the human blood circulation after peanut ingestion.

This can accelerate the growth of cancer cells (15). However, this is a lab-based study where pure lectins were placed on cancer cells.

There have been no human-based studies on the effect of PNA on cancer cells.

Peanuts are also an excellent source of biotin, which is beneficial for the treatment of multiple sclerosis, diabetes, and brain health.

Peanuts also contain resveratrol, which is a powerful antioxidant that increases blood flow and lowers the risk of stroke.

6. Tomatoes

Tomatoes contain lectins, but there is not enough research to confirm if they harm health.

According to a  study, when rats were fed with tomato lectin-rich diet, the lectins bind to the intestinal wall and resist the digestive process (16).

Another study from Ireland found that tomato lectins can cross the gut wall and enter the bloodstream (17).

Some people are known to develop an allergic reaction to tomatoes, but that has no link to their lectin content.

Tomatoes are in fact, a rich source of lycopene that provides many health benefits including a reduced risk for cancer and heart disease.

Tomatoes are also rich in vitamin C, potassium, folate, and vitamin K.

Ways to neutralize lectins?

1. Sprouting

Sprouting beans, grains, and seeds is an excellent way to deactivate lectins. The lectins in most grains and seeds are in the coating.

As they germinate, the coat is metabolized, and thus lectins are eliminated.

2. Soaking

Soak beans and legumes overnight before you cook them. Change the water often and drain and rinse the beans before cooking.

This classic method of preparing beans helps to reduce lectins. Adding baking soda to the soaking water also helps in lowering lectin content.

3. Fermenting

Fermenting helps bacteria to digest and convert harmful substances like lectins. Several soy products like miso, tempeh, natto, and tamare are fermented.

Even some vegetables like cabbage have fewer antinutrients when it is fermented.

4. Cooking

Use a pressure cooker for cooking tomatoes, potatoes, bean, and quinoa to reduce the lectin content.

Is lectin free diet harmful?

Although a lectin free diet is not harmful, it can be very restrictive. Removing foods that contain lectin from your diet can also eliminate essential nutrients.

Fruits and vegetables have many health benefits. They can lower the risk of many health conditions, like heart disease and lung disease. They also help in preventing weight gain.

Vegetarians may find it challenging to follow a lectin-free diet like legumes, nuts, seeds, and whole grains provide plant-based proteins.

You can cook, soak, ferment, and sprout these foods to remove their lectin content.

If you decide that you must go lectin free, eat plenty of highly nutritious lectin-free vegetables like broccoli and avocado. You can also take supplements to improve your nutrient intake.

Final thoughts

Lectins are carbohydrate-binding proteins present in most plants, especially seeds and tubers like cereals, potatoes, and beans.

When eaten in their raw form, lectins can be harmful. Lectins are also known as antinutrients as they can block the absorption of certain nutrients like calcium, iron, phosphorus, and zinc.

Lectins can also have some positive effects. Lectins can help in immune function and cell growth. They also help the good bacteria in the digestive system.

Foods that are high in lectin,  like beans, soy, legumes, tomatoes, and whole grain, are usually recommended as a part of a healthy well-balanced diet.

These foods are high in nutrients and provide a range of health benefits, that outweigh the harmful effects of lectins.

You can neutralize the impact of lectins in these foods by cooking, soaking, fermenting, and sprouting them.