What are Lectins?
Lectins are (sticky) proteins that bind to carbohydrate components on cells. They are found in animals, plants and micro-organisms where they perform important cell recognition and host defence biological functions. For example in plants, lectins may be produced as a survival mechanism. If a predator eats a plant and has a negative reaction, it certainly won't go near that plant again, the lectin has done its job!
Which foods contain Lectins?
Lectins exist in almost all plants. Most fruits, vegetables and wholegrains contain some lectins at varying quantities. Therefore, lectins are a large part of our diet. It would almost be impossible to eat a totally lectin-free diet. Some foods containing higher lectins:
Whole Grains – wheat, quinoa, barley, corn, oats and grain-fed animal foods.
Legumes (raw) – beans (chickpeas, kidney beans, lentils, mung beans, soybeans), peanuts, cashew nuts and peas.
Nuts and seeds – tree nuts (eg-almonds, hazelnuts) and most flowering seeds (eg-sunflower, sesame).
Nightshade plants ( Solanaceae family of flowering plants) – white potatoes, tomatoes, aubergine, red spices, goji berries and peppers.
Why are Lectins a problem?
Lectins can be resistant to digestion and humans need sufficient enzymes to digest them. When consumed in excess by individuals with dysfunctional enzymes, they may become a problem. You may have experienced bloating, wind or indigestion after eating a bowl of chickpeas for example, these symptoms may be a sign of poor digestion.
Lectins bind easily to human tissues. When undigested lectins bind to the cells of the gut barrier (or gut bacteria), they can cause intestinal damage and malabsorption. This is called intestinal permeability and consequently lectins, as well as other food antigens and endotoxins, can cross the gut barrier and enter the blood.
Once lectins are in the blood they upregulate the immune response causing systemic inflammation and production of lectin-specific antibodies. The lectin-IgG or IgA antibodies are now able to bind to various human tissues through a process called molecular mimicry. This sets the stage for Autoimmunity. For example, lectins can bind to the islet cells of the pancreas, resulting in autoimmunity against the islet cells, and causing Type1 Diabetes.
In a recent study, antibodies to lectins were found in the blood of healthy subjects, proving that intact lectins can surpass the gut barrier and enter the blood after the host consumed lectin containing foods.
What are the benefits of Lectins?
Before we demonise lectins too much, many studies demonstrate the beneficial effects of lectin foods on health as part of a balanced diet:
Lectin rich foods are nutrient dense and contain important antioxidants. High in vitamins & minerals such as; potassium, zinc, iron, magnesium and B vitamins. They are a great source of fibre and protein, especially in vegan diets.
Lectin foods are prominent in the traditional diets of 'Blue Zone' areas, which are places around the world where life expectancies are the highest. For example, the Mediterranean and Okinawa diets.
Studies indicate that lectin foods are associated with lower rates of heart disease and type 2 diabetes.
Lectins have immunomodulatory properties, supporting the innate immune system as a first line of defence against pathogens.
Lectins may improve blood sugar regulation by slowing down the digestion and absorption of carbohydrates.
Lectins are anti-microbial and anti-fungal, binding easily to the surface of microbes.
Several studies in mice have indicated an anticancer effect of specific plant lectins.
How should we eat Lectins?
Lectins must not be eaten raw or uncooked as this is when they are in their most potent and reactive state. For example, severe reactions have been seen in people eating even small amounts of raw or undercooked kidney beans. They contain phytohemagglutinin, one of the most reactive lectins.
Lectins from foods may be deactivated or reduced by a variety of methods, some which have been practiced by various cultures for centuries:
Soaking in water - Lectins are water soluble, so exposure to water through soaking may reduce some lectin content.
Cooking - Wet, high-heat methods like boiling or stewing and preferably using a pressure cooker can be sufficient to denature lectin proteins. For example, boiling kidney beans at 100°C for 10 minutes completely destroys the phytohemagglutinin.
Soaking followed by cooking is highly effective. In a study, this method completely destroyed the lectin phytohemagglutinin in different varieties of white beans.
Fermentation can reduce lectins. Fermentation of beans, in one study resulted in a 95% reduction of lectins. Sourdough bread and fermented soy products have become popular, where the fermentation process allows for easier digestion.
Sprouting destroys some lectins. In a study, sprouting reduced the lectin content of white kidney beans by 85%.
Digestive enzymes supplementation - Appropriate cooking may denature lectins so that they become more digestible with the help of enzyme supplements.
Dehulling - Removing the outer hull of grains or beans where lectin content is high. This is done for white rice which is a staple wholegrain eaten all over the world.
Deskinning and deseeding - The highest lectin content is found in skins and seeds, so peeling and deseeding can significantly reduce lectin content eg in tomatoes.
Note - temperatures achieved by slow cookers, especially on low settings, may be inadequate to inactivate lectins. Also, lectins in wheat germ or peanut are heat stable and thus may not be completely inactivated by regular cooking methods.
Should Lectins be avoided in Autoimmunity?
Without a doubt, the evidence suggests foods such as whole grains, legumes, nuts and seeds play a beneficial role in a well-balanced healthy diet, if cooked and prepared properly and eaten in moderation.
However, some individuals, especially those with Autoimmune conditions, may have a failure of oral tolerance to lectins. Quite often in Autoimmunity, intestinal permeability is present making it easier for lectins to cross the barrier, enter the blood and upregulate the immune system. Individuals that report sensitivity to specific lectin foods through obvious symptoms such as bloating and pain, may see improvements once the specific foods are removed from their diet.
Elimination
Lectin food sensitivities can be investigated by elimination (for 1-3 months) and reintroduction of the specific offending foods. Elimination may reduce the stimulus, thereby reducing or even eliminating disease symptoms in some patients. The Autoimmune Paleo (AIP) Elimination diet maybe a useful tool to help with this.
Food sensitivity lab testing
Lab testing for detection of IgA or IgG antibodies against specific lectins may help to quickly identify the offending foods so that they can be removed from an individual's diet. This approach may provide very helpful guidance for those who don't want to spend months doing eliminations. However, they can be costly and not always 100% accurate.
Note - wheat germ, soybeans, red kidney beans, jack beans and peanuts have been studied to contain some of the most reactive lectins in the pathogenesis of Autoimmunity and may be worth avoiding.
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