Lectins: Why everyone is now afraid of tomatoes and whole grains

What are lectins?

Lectins are proteins or glycoproteins that are present in some plant-based foods and serve as defense substances for the plant. Lectins have been known in nutritional science for years, as well as their effects on humans. They can be toxic, bind to our intestinal cells, and make them more permeable to harmful toxins (leaky gut syndrome). People with weak immune systems are said to be particularly susceptible to this.

That's why lectins harm us.

Once they enter our body and reach the blood, they also bind to other cells, such as our red blood cells, which then clump together and hinder the transport of oxygen and nutrients. Therefore, lectins are also referred to as anti-nutrients because they themselves have no nutritional value, but can prevent the absorption of other important nutrients. Where they attach in the human body, they can fuel inflammatory reactions and are therefore also associated with autoimmune diseases such as Crohn's disease, multiple sclerosis, or irritable bowel syndrome.

These foods contain lectins.

Legumes are among the foods that contain particularly high levels of lectins. Even a few raw beans can harm the body and cause severe intestinal inflammation or even be fatal to humans. Lectins are also present in fresh green beans, and they should only be eaten cooked. Grains, cashews, peanuts, as well as nightshades such as tomatoes, bell peppers, eggplants, and potatoes also contain lectins, albeit in smaller amounts than legumes. The lectin in wheat is considered particularly heat-resistant. Lectins and gluten should not be confused, even though lectins are sometimes referred to as the "new gluten." Overall, whole grains contain slightly more lectins than refined flour, but even baguettes and white bread still contain lectins. The good news is that through proper preparation, we can mitigate the harmful effects of lectins.

Cooking destroys (most) lectins.

Cooking destroys lectins in legumes and vegetables. When legumes are soaked in water for a long time, a large part of the lectins is already dissolved. Enzymatic processes such as kneading dough or fermenting vegetables also help to neutralize the anti-nutrients. For grains, it is important to prepare the dough as long as possible - as per old artisan tradition - and let it rise for a long time, for example, several hours or overnight. This is often not the case with industrial bread made with artificial leavening agents. You can find more information and a recipe for "slowly" baked bread here.

And tomatoes or cashews that are not eaten heated?

In tomatoes, peanuts, and cashews, the content of lectins is much lower. These amounts do not harm healthy individuals, so we can eat them without worry. Research is currently being conducted on the positive effects of lectins. There is evidence suggesting that these proteins can help prevent colon cancer. As with many things in nutrition, the dose makes the poison. What is healthy and digestible for one person may still cause discomfort for others.

Who should better abstain?

If you have a sensitive gut or suffer from autoimmune diseases, you can try to see if your symptoms improve by avoiding foods containing lectins. It is also advisable to test if bell peppers and tomatoes are better tolerated when cooked, and to possibly roast peanuts and cashews in a pan for a few minutes.

Knowledge at a glance

• Lectins are proteins found in plants that can bind to carbohydrate structures in our intestines or in our blood, triggering inflammation.

• Legumes such as lentils and beans, fresh green beans, wheat, cashews, and peanuts, as well as nightshades like tomatoes and eggplants, contain lectins.

• Most lectins are destroyed by cooking. Exception: The lectin in wheat - agglutinin - is particularly heat-resistant.