I grew up eating baked beans, whole grain bread, oatmeal, and barley. I love the glorious smoothness and flavour of a well-blended chickpea hummus – yum. Turns out humans have been eating pulses, a.k.a. legumes (chickpeas, lentils, dried peas and beans), seeds and grains for quite a long time. Archaeological evidence puts lentils in Egyptian pyramids and pulses in the Punjab area of Asia around 3300 BC; clearly our ancestors where on to something. However, if we’re to believe any of the internet chatter these days, something about these foods is bad – cue yet another dietary fad: lectin avoidance for everyone.
What are lectins?
Lectins are a group of proteins found in every living thing such as plants, bacteria, and foods (legumes/pulses, seeds and grains especially) – most are harmless. Even though they’re found in all foods, only about 30% of our diet contains lectins in meaningful amounts. In human physiology, lectins seem to play a beneficial role in immune function, cell growth, and regulating inflammation.
Lectins in the United States diet: a survey of lectins in commonly consumed foods and a review of the literature.
In plants, the role of lectins is not fully understood but they appear to be a deterrent to being eaten by microorganisms, insects and animals. By having compounds that can cause indigestion and intestinal damage, animals may think twice before coming back for seconds. When it comes to seeds, it’s thought that lectins help plants to be ‘fruitful and multiply’; foraging animals eat the seeds which pass through their digestive tracts unchanged, allowing them to be dispersed ‘around town’ via stool.
So what’s the hubbub about lectins?
Like any health fad, most have a seed of truth within them. Just as lectins can cause problems for animals, humans are potentially vulnerable to their toxicity too. They can cause problems for the digestive tract by binding to intestinal cells which may lead to cellular dysfunction and increased inflammation. Lectins are also resistant to human digestion and can enter the blood stream unchanged.
Because some lectins, such as phytohaemagglutinin, found mostly in uncooked (raw) or improperly prepared red and white kidney beans, can lead to kidney bean poisoning (abdominal pain, vomiting and diarrhea), lectins have gotten a bad rap.
Red kidney bean poisoning in the UK: an analysis of 50 suspected incidents between 1976 and 1989
On a side note, this is why you’ll never see sprouted [raw] red kidney beans as a food. Good to know.
Since plant foods have been part of the human diet for millennia, we’ve evolved some protection against them; the immune system products lectin antibodies and virtually everybody on the planet has these antibodies in their system. However, like anything, there’s a lot of variation between people and their ability to tolerate foods rich in lectin such as nightshades (tomato, potato, eggplant, bell peppers, etc), as well as, wheat and other grains, and pulses (chickpeas, lentils, dried peas and beans). Ask any nutritional professional who works with digestive issues.
Antibodies and Lectins in Glycan Analysis
Another reason many have a hate-on for lectins is because they are part of a group of plant compounds called anti-nutrients; these reduce the body’s ability to absorb essential nutrients, primarily minerals like zinc, iron, calcium etc. Examples include phytic acid/phytates, tannins, protease inhibitors, and oxalate. This is why we have standard advice to anyone who’s trying to increase their iron absorption to avoid drinking tea [tannins] with meals as tannins can reduce the iron in food from being absorbed. In fact, hating on anti-nutrients is a central paleo diet tenet as outline here. It’s true that anti-nutrient could be an issue with extreme diets, anyone old enough to remember the macrobiotic diet? But to be clear, for the vast majority of people, anti-nutrients aren’t a problem.
It’s because of these casual observations than many self-stylized ‘health gurus’ have made sweeping generalizations about lectins and why they should be avoided by everyone.
What does the research say?
Under certain conditions, dietary lectins can be problematic. High intakes of lectin-containing foods can irritate the digestive tract which may aggravate certain intestinal conditions like inflammatory bowel disease (Crohn’s and Colitis) or IBS.
Modulation of immune function by dietary lectins in rheumatoid arthritis
Because lectins have been shown to increase the permeability of the intestinal tract (the small intestines become more porous allowing lectins to enter the blood stream), lectins can stimulate the immune system and trigger it to produce antibodies against the lectins and the tissues that the lectins might be attached to. This is how dietary lectins may be a problem for those with autoimmune diseases such as Celiac disease, rheumatoid arthritis, and lupus for example. Some studies have found a benefit for this subgroup of people when they followed a lectin-reduced or lectin-free diet when their disease is more active.
Intestinal permeability, leaky gut and intestinal disorders
Of course we know that the vast majority of people can confidently enjoy lectin-containing pulses, grains and seeds including those with potential health conditions that might make them more sensitive to them when they’re well. This shouldn’t be a surprise or sound shocking; this is true for any food. Not all foods can be eaten, by all people, all of the time but that doesn’t mean lectins should be shunned carte blanche.
Do you need to avoid lectin-containing foods?
In a word; no. On their own, lectins are a challenge to the human digestive tract. This is why we smart humans have figured out ways to neutralize lectins so that we can reap the nutritional benefits from the foods they’re found in. Several preparation methods can reduce the lectin content of foods up to 90% or more making them suitable for consumption which is good news as I’m not prepared to give up my hummus. Soaking, cooking [boiling and heating] and fermentation degrades most of the lectins in foods.
Lectins can be a toxic and problematic when eaten in large amounts, and/or from raw foods; fortunately we don’t eat large amounts of them unless someone is being a bit extreme with a raw diet and and we use a variety of preparation methods when making food. For the vast majority of us, there’s no reason to avoid nutritious foods like whole grains, pulses, and seeds, however;
just as it’s a load of crap for anti-lectin fans to be telling everyone to avoid them, it’s equally overly simplistic to say lectins are nothing to worry about, ever…
People with autoimmune and digestive disease may do better on a lectin-reduced/lectin-free diet even if only temporarily during flares or increased disease activity. An integrative & functional nutritionist who’s knowledgeable in gut health issues, food intolerances and elimination diets can help plan a nutritionally balance diet in cases like this. The amount of lectins normally found in our diets is safe and of no consequence for the vast majority of people.