Updated: Jul 31, 2020
Lectins are an "anti-nutrient" that have received a lot of media attention recently. Fad diet books cite this food component as one of the central causes of obesity, chronic inflammation, and autoimmune conditions.
I actually find this slightly ironic, because when we look at where lectins come from, they're all from plant-based foods. But if we actually look at the statistics of how much Australian's eat plant-based foods, 95% of adults aren't actually meeting the fruit and vegetable recommendations.
So the claims that lectins are the cause of all of these diseases already isn't making sense (1).
So what are lectins?
Lectins are a protein found in plant foods that bind to carbohydrates. They resist being broken down in the gut and are stable in acidic environments (such as our stomach). This is actually a feature that helps to protect lectic-containing plants in nature (2).
Where are they found?
Lectins are found in varying amounts in most plants. This includes beans, pulses, grains, fruits and vegetables, nuts, coffee, chocolate some herbs and spices. Pulses (think chickpeas, lentils, kidney beans) and grains (like rice and quinoa) contain the highest amount compared with other foods.
Why are they a problem?
When consumed, lectins can cause negative side effects. One of the most commonly reported reaction is found when eating raw or uncooked kidney beans. Kidney beans contain a type of lectic called phytohaemagglutinin. Ingestion of this can cause red blood cells to clump together as well as nausea, vomiting, stomach upset and diarrhea (3).
Lectins have also been shown to interfere with the absorption of minerals including iron, calcium, phosphorus, and zinc.
Some research has also indicated that they may bind to the cells lining the digestive tract. Over time, this may effect the intestinal flora and is theorized to play a role in inflammatory conditions such as type 1 diabetes and rheumatoid arthritis (3,4).
That sounds pretty bad, should I be worried?
Unsurprisingly, these theories have fuelled the profits of books and enzyme supplements from the anti-lectin movement. There is very limited research in humans about the number of active lectins consumed in the diet and their long term health effects.
Lectins in foods are most often studied in developing countries where there is high levels of malnutrition, limited cooking facilities and lack of dietary variety (5,6).
There are different forms of lectins found in different foods. The reactions people have to them vary significantly.
Some people with digestive conditions such as Irritable Bowel Syndrome may be more likely to experience some negative symptoms from lectins and other anti-nutrients. However, a reasonable suggestion is simply to eat less of the food causing the digestive problem (ps. see a dietitian to help you with this).
Do they have any benefits?
Lectins can also act as a powerful antioxidant. Antioxidants help to protect cells from damaging unpaired electrons known as free radicals. This antinutrient can also help slow down the digestion and absorption of carbohydrates. This helps to stabilise blood sugar levels and keeps you fuller for longer.
Emerging research has also looked into the beneficial effect low amounts of lectins on stimulating gut cell growth in patients who are unable to eat for long periods (3,7)
Researchers are also investigating the effects that lectins may have in the treatment of cancer and even could be used in antitumor drugs in the future (8).
In addition to this, research time and time again continues to show the benefits of eating whole grains and legumes. People who consume more whole grains have improved cardiovascular health outcomes. Eating legumes such as chickpeas, lentils and kidney beans are linked with supporting healthy body weight and reducing CRP inflammatory markers.
Preparing food to minimise lectins
It is quite rare to eat foods with a high amount of lectins. This is due to them being most potent in the raw state of foods and these foods not typically consumed raw.
When foods are cooked, especially at high heat using a liquid such as cooking, stewing, boiling or soaking, this inactivates most lectins. They are also water-soluble and found on the outer surface of the food. This means, when these foods are cooked, the exposure to water removes the lectins.
The body also has a fantastic ability to produce enzymes during digestion that helps to break them down.
When cooking beans in a crock pot, use canned beans or boil them for at least 30 minutes before putting in the crockpot.
The bottom line
Just don't eat grains are legumes raw.
Lectins are certainly harmful when consumed. However, given that they are denatured during cooking and the evidence against limiting these foods from our diet is very weak, it is definitely not something to be concerned about. Just make sure to cook your food!
There is strong evidence supporting the health benefits of pulses, grains, nuts, fruits and vegetables (i.e even in foods where lectins are found). If removed in a "lectin-free" diet, this could potentially lead to nutritional deficiencies.
If you're following a plant-based or vegan diet and experiencing digestive upset, take control and apply to work with one of our expert plant-based dietitians. .
1. 4364.0.55.001 - National Health Survey: First Results, 2014-15. (2020). Retrieved 3 February 2020, from https://www.abs.gov.au/ausstats/abs@.nsf/Lookup/by%20Subject/4364.0.55.001~2014-15~Main%20Features~Daily%20intake%20of%20fruit%20and%20vegetables~28
2. Peumans, W., & Van Damme, E. (1995). Lectins as Plant Defense Proteins. Plant Physiology, 109(2), 347-352. doi: 10.1104/pp.109.2.347
3.Vasconcelos, I., & Oliveira, J. (2004). Antinutritional properties of plant lectins. Toxicon, 44(4), 385-403. doi: 10.1016/j.toxicon.2004.05.005
4. Freed, D. (1999). Do dietary lectins cause disease?. BMJ, 318(7190), 1023-1024. doi: 10.1136/bmj.318.7190.1023
5. Gibson, R., Bailey, K., Gibbs, M., & Ferguson, E. (2010). A Review of Phytate, Iron, Zinc, and Calcium Concentrations in Plant-Based Complementary Foods Used in Low-Income Countries and Implications for Bioavailability. Food And Nutrition Bulletin, 31(2_suppl2), S134-S146. doi: 10.1177/15648265100312s206
6. Roos, N., Sørensen, J., Sørensen, H., Rasmussen, S., Briend, A., Yang, Z., & Huffman, S. (2012). Screening for anti-nutritional compounds in complementary foods and food aid products for infants and young children. Maternal & Child Nutrition, 9, 47-71. doi: 10.1111/j.1740-8709.2012.00449.x
7. Liu, Z., Luo, Y., Zhou, T., & Zhang, W. (2013). Could plant lectins become promising anti-tumour drugs for causing autophagic cell death?. Cell Proliferation, n/a-n/a. doi: 10.1111/cpr.12054
8.Sarup Singh, R., Preet Kaur, H., & Rakesh Kanwar, J. (2016). Mushroom Lectins as Promising Anticancer Substances. Current Protein & Peptide Science, 17(8), 797-807. doi: 10.2174/1389203717666160226144741