Lectins are a type of protein found in all forms of life, including the food you eat.

In small amounts, they may provide several health benefits. However, larger amounts can reduce your body's ability to absorb nutrients.

This article reviews 6 foods that are particularly high in lectins and explains how you can make sure they don't reduce your nutrient absorption.

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What are lectins?

Lectins are a type of protein that can bind to sugar.

They're sometimes referred to as antinutrients. Animal studies suggest that certain lectins can reduce the body's ability to absorb nutrients. Lectins are thought to have evolved as a natural defense in plants, essentially as a toxin that deters animals from eating them (1).

Lectins are found in many plant- and animal-based foods, yet only about 30% of the foods you eat contain significant amounts (2).

Humans are unable to digest lectins, so they travel through your gut unchanged.

How they work remains a mystery, though animal research shows certain types of lectins bind to cells on the gut wall. This allows them to communicate with the cells, triggering a response.

Animal lectins play important roles in several bodily processes, including immune function and cell growth.

Research suggests that plant lectins could even have a role in cancer therapy (3).

However, eating large amounts of certain types of lectins can damage the gut wall. This causes irritation that can result in symptoms like diarrhea and vomiting. It can also prevent the gut from absorbing nutrients properly.

The highest concentrations of lectins are found in healthy foods like legumes, grains, and nightshade vegetables. Luckily, there are several ways to reduce the lectin content of these healthy foods to make them safe to eat.

Research shows that by cooking, sprouting, or fermenting foods that are high in lectins, you can easily reduce their lectin content to negligible amounts (4, 5, 6).

Below are 6 healthy foods that are high in lectins.

1. Red kidney beans

Red kidney beans are among the richest sources of plant-based protein.

They are also a great source of carbs that are low on the glycemic index (GI).

This means that they release their sugars more slowly into your blood, causing a gradual rise in blood sugar rather than a sharp spike (7).

What’s more, they’re also high in resistant starch and insoluble fiber, which can aid weight loss and improve general gut health (8, 9, 10).

Red kidney beans contain many vital vitamins and minerals, such as iron, potassium, folate, and vitamin K1.

However, raw kidney beans also contain high levels of a lectin called phytohaemagglutinin.

If you eat them raw or undercooked, they can cause extreme nausea, vomiting, and diarrhea. As few as five beans can cause a response.

A hemagglutinating unit (hau) is a measure of lectin content. In their raw form, red kidney beans contain 20,000–70,000 hau. Once they're thoroughly cooked, they contain only 200–400 hau, which is considered a safe level (4).

When properly cooked, red kidney beans are a valuable and nutritious food that shouldn't be avoided.

Summary Red kidney beans are high in protein and fiber. When cooked properly, they're a healthy and valuable addition to the diet.

2. Soybeans

Soybeans are a fantastic source of protein. They contain one of the highest quality plant-based proteins, which makes them particularly important for vegetarians (11).

They are a good source of vitamins and minerals, particularly molybdenum, copper, manganese, magnesium, and riboflavin.

They also contain plant compounds called isoflavones, which have been linked to cancer prevention and a decreased risk of osteoporosis (12, 13).

Research shows soybeans can also help lower cholesterol and reduce the risk of obesity and type 2 diabetes (14, 15, 16).

That said, soybeans are another food that contains high levels of lectins.

As with red kidney beans, cooking soybeans nearly eliminates their lectin content. Yet, make sure you cook them for long enough at a high enough temperature.

Research shows that soybean lectins are almost completely deactivated when they're boiled at 212°F (100°C) for at least 10 minutes.

In contrast, dry or moist heating of soybeans at 158°F (70°C) for several hours had little or no effect on their lectin content (17).

On the other hand, fermentation and sprouting are both proven methods of reducing lectins.

One study found that fermenting soybeans reduced the lectin content by 95%. Another study found that sprouting decreased the lectin content by 59% (5, 6).

Fermented soybean products include soy sauce, miso, and tempeh. Soybean sprouts are also widely available and can be added to salads or used in stir-fries.

Summary Soybeans are a fantastic source of high-quality protein, vitamins, minerals, and isoflavones. You can drastically reduce their lectin content by cooking, fermenting, and sprouting them.

3. Wheat

Wheat is the staple food for 35% of the world's population (18).

Refined wheat products have a high glycemic index (GI), meaning they can cause your blood sugar levels to spike. They've also been stripped of virtually all nutrients.

Whole wheat has a similar GI, but it's higher in fiber, which can benefit your gut health (19).

Some people are intolerant to gluten, a collective term referring to many types of protein found in wheat. However, if you tolerate it, whole wheat can be a good source of many vitamins and minerals, such as selenium, copper, and folate.

Whole wheat also contains antioxidants like ferulic acid, which has been linked to a lower incidence of heart disease (20).

Raw wheat, especially wheat germ, is high in lectins, with around 300 mcg of wheat lectins per gram. However, it appears that the lectins are almost eliminated by cooking and processing (21).

Compared to raw wheat germ, whole-wheat flour has a much lower lectin content at about 30 mcg per gram (21).

When you cook whole-wheat pasta, it appears to completely inactivate the lectins, even at temperatures as low as 149°F (65°C). In cooked pasta, lectins are undetectable (21, 22).

Moreover, research shows that store-bought, whole-wheat pasta doesn't contain any lectins at all, as it's usually exposed to heat treatments during production (22).

Since most whole-wheat products you eat are cooked, it’s not likely that lectins pose a significant problem.

Summary Wheat is a staple in many people's diets. Whole-wheat products can provide many health benefits. Their lectin content is nearly eliminated during cooking and processing.]

4. Peanuts

Peanuts are a type of legume that’s related to beans and lentils.

They are high in mono- and polyunsaturated fats, making them a great source of energy.

They are also high in protein and a wide range of vitamins and minerals, such as biotin, vitamin E, and thiamine.

Peanuts are also rich in antioxidants and have been linked to health benefits like a reduced risk of heart disease and gallstones (23, 24, 25).

Unlike some of the other foods on this list, the lectins in peanuts don't appear to be reduced by heating.

A study found that after participants ate 7 ounces (200 grams) of either raw or roasted peanuts, lectins were detected in their blood, indicating that they had crossed through from the gut (26).

One test-tube study found that peanut lectins increased growth in cancer cells (27).

This, alongside the evidence that peanut lectins can enter the bloodstream, has led some people to believe that lectins could encourage cancer to spread in the body.

However, the test-tube study above was carried out using high doses of pure lectins placed directly onto cancer cells. No studies have investigated their exact effects in humans.

Thus far, the evidence demonstrating peanuts' health benefits and role in cancer prevention is far stronger than any evidence of potential harm.

Summary Peanuts are a great source of protein, unsaturated fats, and many vitamins and minerals. Although peanuts contain lectins, evidence of their health benefits is far stronger than that of any risks.

5. Tomatoes

Tomatoes are part of the nightshade family, along with potatoes, eggplants, and bell peppers.

Tomatoes are high in fiber and rich in vitamin C, with one tomato providing approximately 20% of the daily value. (28).

They are also a decent source of potassium, folate, and vitamin K1.

One of the most studied compounds in tomatoes is the antioxidant lycopene. It has been found to reduce inflammation and heart disease, and studies have shown it may protect against cancer (29, 30, 31).

Tomatoes also contain lectins, though there is currently no evidence that they have any negative effects in humans. The available studies have been conducted on animals or in test tubes.

In one study in rats, tomato lectins were found to bind to the gut wall, but they didn't appear to cause any damage (32).

Another study in mice suggests that tomato lectins do manage to cross the gut and enter the bloodstream once they've been eaten (33).

Indeed, some people appear to react to tomatoes, but this is more likely due to something called pollen food allergy syndrome or oral allergy syndrome (34).

Some people have linked tomatoes and other nightshade vegetables to inflammation, such as that found in arthritis. So far, no formal research has supported this link.

Lectins have been linked to rheumatoid arthritis, but only in those who carry genes that put them at a high risk of the disease. The research found no link between rheumatoid arthritis and nightshade vegetables, specifically (35).

Summary Tomatoes are full of vitamins, minerals, and antioxidants, such as lycopene. There is no evidence that their lectin content has any significant adverse effects in humans.

6. Potatoes

Potatoes are another member of the nightshade family. They are a very popular food and eaten in many forms.

Eaten with the skin, potatoes are also a good source of some vitamins and minerals.

They contain high levels of potassium, which has been shown to decrease the risk of heart disease. They are also a good source of vitamin C and folate.

The skins, in particular, are high in antioxidants, such as chlorogenic acid. This compound has been associated with a reduced risk of heart disease and type 2 diabetes (36).

Potatoes have also been shown to be more satiating than many other common foods, which can aid weight loss. That said, it’s important to consider how they are cooked (37).

As with tomatoes, some people report experiencing adverse effects when they eat potatoes. Animal and test-tube studies have shown that this could be linked to lectins. However, more studies in humans are needed (38).

In most people, potatoes do not cause any adverse effects. In fact, one study found that some varieties of potatoes were linked to a reduction in inflammation (39).

Summary Potatoes are nutritious and versatile. Although they contain high levels of lectins, there is currently no evidence of any significant adverse effects in humans.]

The bottom line

Only about a third of the foods you eat likely contain a significant amount of lectins.

These lectins are often eliminated by preparation processes like cooking, sprouting, and fermentation. These processes make the foods safe, so they will not cause adverse effects in most people.

Nevertheless, nightshade vegetables may cause problems for some people. If you're one of them, you may benefit from limiting your intake.

All the foods discussed in this article have important and proven health benefits.

They're also important sources of vitamins, minerals, and antioxidants. Currently, knowledge about their lectin content indicates there is no need to avoid them.