Are Lectins Bad for Your Gut Health?

Are Lectins Bad for Your Gut Health?
Nutrition
Gut Health
Written By:
Sarah Bullard, MS, RD

Lectins are not bad for gut health if handled appropriately. Research has shown apparent benefits and some drawbacks for plant foods that contain ‘anti-nutrients’ like lectins, oxalates, phytates, and tannins.1 

Anti-nutrients from plants can be harder for the body to digest and may reduce the bioavailability of key nutrients. Consumption of large amounts of anti-nutrients can multiply this effect.1 Some diets discourage the eating of lectins in any amount. 

We will discuss the healthfulness of lectins, specifically in relation to gut health and function. 

What are Dietary Lectins?

Dietary lectins, or plant hemagglutinins (PHA), are proteins that bind to carbohydrates and are found in all plants. This protein-carbohydrate bond protects the plant in the wild but can cause more difficulty with digestion in humans. 

When eaten uncooked and raw, the lectins pass through the gastrointestinal tract unchanged. As lectins reach the small intestine, they can bind to receptors on the intestinal cell lining and cause damage.1

Larger amounts of lectins are found in certain plant foods like legumes, wheat, seeds, nuts, and some fruits and vegetables. Different cooking and preparation methods reduce the lectin content of these foods. 

Additionally, depending on the cultivation area, bean maturity, and plant variety, significant variations in lectin levels were found within the same bean (kidney bean).1 This makes it hard to predict the exact lectin content of plant foods accurately. 

Are Lectins in Food Good or Bad for You?

First, the bad, then the good. Lectins are harmful to you when eaten raw or undercooked. There are well-documented cases of food poisoning worldwide. PHA toxicity can occur after eating as few as 3 or 4 raw kidney beans. Symptoms include nausea and vomiting shortly after eating and then diarrhea. People typically recover within 3 to 4 hours. The PHA can cause red blood cells to clump together when eaten raw.1 No PHA toxin is present if the beans have been boiled for a minimum of 10 minutes. 

Animal studies have shown that after consuming raw beans or raw bean flours, intestinal alterations were seen, including reduced enzyme activity, microvilli changes, and intestinal damage from PHA toxicity.1 

However, these effects are not seen when the lectin-rich plant foods are cooked in specific ways! In human studies using cooked whole beans, there are no indications of intestinal changes, as seen with the raw lectin consumption in animal studies. 

Research shows actual benefits from the consumption of foods high in lectins. Animal studies using cooked legume lectins have demonstrated the anti-proliferative activity against various cancers.2 Additionally, diets high in legumes and whole grains are associated with reduced inflammation markers in animals and humans.1 

Beans and other lectin plant foods contain beneficial protein, carbohydrates, prebiotic fiber, vitamins, and minerals and are labeled as antioxidants.3 Consuming this nutrient mix helps to reduce insulin and blood glucose levels. Extensive human studies highlight the benefits of lectin-rich foods like whole grains, nuts, and legumes in managing type 2 diabetes, heart health, blood pressure, and inflammation.4 

Are Lectins Bad for Your Gut?

When eaten raw, lectins are harmful to your gut. These active lectins can cause intestinal damage. They may also interfere with the absorption of crucial minerals like zinc, calcium, phosphorus, and iron. Poor gut health and intestinal damage are often a precursor for autoimmune diseases.5 

In reality, the chance of a large active (raw) intake of lectin-rich foods is low. Lectins are heat sensitive and water-soluble. Food naturally high in lectin tastes terrible uncooked, which is a wonderful protective feature. 

Traditional cooking methods for dry beans call for several hours of soaking, followed by several hours of boiling. This process removes active lectins to negligible levels. Canned beans have already undergone this process and are low in lectins. Lectins are not harmful to most people when consumed properly. 

Food High in Lectins

About one-third of our food contains lectins. These include legumes, wheat, seeds, nuts, and some fruits and vegetables. Many foods contain higher lectin levels in their raw, uncooked form. These lower to safe levels after cooking.

Red kidney beans contain the highest amount of lectins in their raw state at 20,000 to 70,000 hau (hemagglutinating unit). Once cooked, they have a safe level of 200-400 hau.6 

Research on 32 different lectin-containing plant foods showed no detectable levels of lectin after cooking, except for nigella seeds (26 hau), broad green beans (26 hau), and tomatoes (104 hau).7 These are within the safe level. 

This list entailed bell peppers, eggplant, green beans, peas, potatoes, sugar peas, sugar snaps, tomatoes, barley, 20 different beans/legumes/lentils, four varieties of quinoa, various seeds, and wheat. Each lentil or legume was soaked for 10 to 12 hours, followed by 30 to 60 minutes of boiling. Different cooking times are listed within the study for the other plant foods.7 

Of note, 18 food items were within the safe level before cooking. Those containing high lectins before cooking included beans, lentils, and potatoes. These plant foods are within safe lectin levels once cooked. 

Lectins and Leaky Gut

Our gut (or intestinal cells) are made to absorb water and nutrients from our food and transfer these vital components to the bloodstream and body systems.  A leaky (or more permeable) gut allows more water, nutrients, and possibly toxins to pass through.8 

Combining a genetic predisposition with a leaky gut may allow for the trigger of the start and development of autoimmune diseases like type 1 diabetes, rheumatoid arthritis, and lupus.8 

Research indicates adequate vitamin D protects the intestinal wall, while stress can induce leaky guts. Some types of stress listed are burns, chronic alcohol consumption, and infections. This can all lead to increased intestinal permeability and the transfer of bacteria inside the cell wall. This transfer can trigger an abnormal immune response, leading to inflammation, tissue damage, and the activation or progression of autoimmune disorders.8

Research on lectins and their role in a leaky gut is not conclusive and limited. Some research indicates that the undigested lectins from plant-based foods can travel into some individuals' blood, trigger an immune response, and cause problems like autoimmune disorders.9 

Per the study results, lectins may be problematic for 8 to 15% of the population but are usually in conjunction with noted intolerance to eating foods with lectin.9 Therefore, it is recommended that if you show signs of intolerance (bloating, gas, physical discomfort), to consider eliminating or reducing lectin-rich foods. You may be part of the population whose immune system responds to lectin negatively.

Takeaways

  • The consumption of raw or undercooked lectins (most commonly found in legumes) is dangerous for all people leading to food poisoning and intestinal cell damage. 
  • Cooking lectin-rich foods reduces the lectin to a low or non-existent level, making them safe for most of the population. 
  • Consuming foods containing lectins has been associated with preventing cancer progression2 and managing type 2 diabetes, heart health, blood pressure, and inflammation.4 
  • Lectins are present in foods that provide many proven health benefits and are a good source of nutrients. The benefits of foods containing lectins currently outweigh the risks.
  • If you show signs of intolerance after eating foods high in lectins, consider eliminating or reducing your intake with the help of a registered dietitian. You may need to eliminate certain types instead of all food containing lectins.

Nourish is here to help

Navigating nutrition can be challenging, and diet can play a key role in quality of life, but it differs from person to person. That’s why it’s important to work with a nutritionist who can tailor a nutrition plan that’s as unique as you are. 

At Nourish, we help people achieve health and wellness through virtual, personalized nutrition counseling. Our services are covered by insurance and 100% remote. Click here to get in touch and book an appointment today!

References:

  1. NIH Anti-Nutrients
  2. NIH Structure Function Lectins
  3. NIH Bioactive Compounds
  4. NIH Nutritional Quality of Legumes
  5. NIH Lectins and Autoimmune reactions
  6. FDA
  7. Lectin Activity in Plant Based Foods
  8. NIH Gut Microbiota
  9. NIH Lectin Specific Antibody