You may never have heard of lectins before, but you’ve eaten foods containing them many times. Here’s what they are, and what they mean for your thyroid health.
by Dr. Vedrana Högqvist Tabor
What are lectins?
Lectins are natural proteins that can be found in many fruits and vegetables, especially potatoes, beans, nuts, and seeds (1). There are several different types of lectins, some of which can cause gut inflammation (2). Humans cannot digest lectins (2), but even undigested they don’t simply pass through the gut on the way out. They actually can end up in the bloodstream and cause ongoing inflammation in different parts of the body (3).
Lectins, autoimmune disease, and thyroid health
Lectins can specifically trigger thyroid cells to “talk to” immune cells, and attract them to the thyroid gland, a similar process to what happens in the pancreas of a person with diabetes (4). This is considered one of the early steps in the autoimmune destruction of the thyroid.
Lectins have been studied extensively in rheumatoid arthritis (RA), and lectin found in wheat is one of the most common food triggers for RA patients (5).
Lectins are indeed very toxic to the gut; they stick to and peel off the gut protective layer called mucosa, which then causes bad bacteria to grow uncontrollably and many other food particles to pass through the otherwise tight gut barrier (6). This is one form of leaky gut.
Lectin activity might be a good explanation of why Hashimoto’s occurs after people have long-term or recurrent infections: lectins block mucosa, which is the natural barrier and protector against bacteria and viruses not only in the intestine, but also in the throat (7). This creates a prolonged state of inflammation which can re-program the immune system and lead to autoimmune condition.
The Paleo diet aka the stone age diet
If you don’t suffer from food sensitivities or allergies, the paleo diet or a diet avoiding starch is a good option to remove lectins from the gut (8).
Some researchers classify lectins as anti-nutritional, as they cannot be digested. They bind to the gut cells and not only prevent digestion of other foods but also change the bacterial balance in the gut. In addition, they can alter the body’s hormonal balance. If eaten in large quantities they can cause damage that is not easily fixed (9).
Approximately 30% of food contains lectins, some of which can cause nutrient deficiencies. They cause gut damage, which is the first step in developing different types of autoimmunities.
Some people find reducing their consumption of food with lectins helps their autoimmune symptoms, but it does not work for everyone (10).
Foods high in lectins
1. Legumes (beans)
Lectins are found in many legumes, including Escumite beans, dark red kidney beans and french beans (11).
Legumes are otherwise rich in vitamins and minerals, as well as in fiber, and for that reason are a great addition to your food. However, their high lectin content might make them problematic in the long run.
Make sure you cook beans well before eating, as the cooking process destroys lectins.
2. Certain nuts
Nuts such as almonds, cashew nuts, and peanuts have high levels of lectins. They are also a great source of biotin, vitamin B1 (thiamine), and vitamin E. While cooking will destroy the lectins in beans, this is not the case for lectins from nuts.
It might still be good to eat nuts in smaller quantities, or replace them with other foods.
For all their health benefits, soybeans pose a few health risks, including being high in lectins.
If you boil soybeans for 10 minutes, it will reduce the lectin content.
Wheat is a great source of selenium and vitamin B9 (folate), but it also contains a high dose of lectins, which can be reduced by processing in high heat.
5. Nightshades: tomatoes, potatoes, eggplants, and bell peppers
The entire nightshade family is rich in vitamins, minerals, and antioxidants, and is very nutritious. They also have a high concentration of lectins, and even worse, these specific lectins seem to be heat resistant; at least half of the lectin content remains after heat processing.
What to do with lectins?
Lectins are important for plants, as they are a natural anti-insect protection for growing crops and plants (11).
Foods high in lectins, also have high nutritional value, and can greatly contribute to making you healthier and more resistant to some of viral and bacterial threats.
Before deciding to get rid of all the lectin-containing foods, experiment and observe which specific lectin you are sensitive to. There are many different lectins, and they react with the body in different ways.
Trying an elimination diet for 2 weeks and tracking your symptoms in BOOST Thyroid app can help you to understand how your symptoms change while testing a specific diet.
Freed DJ. Do dietary lectins cause disease? 1999
Van Damme EJM, et al. Handbook of plant lectins: properties and biomedical applications, 1988
Wang Q, et al. Identification of intact peanut lectinin peripheral venous blood, 1998
What triggers auto-immunity? 1985
Bond A, et al. Distinct oligosaccharide content of rheumatoid arthritis derived immune complexes, 1997
Banwell JG, et al. Bacterial overgrowth by indigenous microflora in the PHA-fed rat, 1988
Uchigata Y, et al. Pancreatic islet cell surface glycoproteins containing Gal β(1–4)GNAc-R identified by cytotoxic monoclonal antibodies, 1987
Freed DLJ, et al. Mucotractive effect of lectin, 1978
Vasconcelos IM, et al. Antinutritional properties of plant lectins, 2004
Vojdani A. Lectins, agglutinins, and their roles in autoimmune reactivities, 2015
Lam SK, et al. Lectins: production and practical applications, 2011