Lectins: Are These Food-Based Proteins Friend or Foe?

John Watson; Reviewed by Anya Romanowski, MS, RD


August 17, 2018

In This Article

The seemingly endless search for that one insidious element in our diets, which if eliminated, can restore our waistlines, health, and happiness has uncovered its latest culprit: lectins. If you have never heard of lectins, carbohydrate-binding glycoproteins found in many foods, prepare to get familiar with what some are deeming "the next gluten."[1]

And as with going gluten-free, there is a slew of information online and elsewhere about the lectin-free diet that experts say has at best a tangential relationship with the scientific evidence.

What follows is a primer on this emerging dietary trend to help you understand whether lectins are friend, foe, or something entirely more interesting.

An Unlikely Antagonist

Lectins are proteins that can be found in most living organisms, and were first discovered in the late 1880s. Certain lectins possess an inherent toxicity thought to have evolved as a natural deterrent to protect plants and animals from being eaten. It appears to be working, because several animal species have been shown to experience reduced intestinal absorption and resulting morbidity after ingesting lectins.[2] Essentially, lectin toxicity mirrors the effect of food poisoning, and serves as an evolutionary caution sign.

But this is in no way true of all lectins, whose range is considerable. Most lectins are inactive with no biological activity, whereas others are thought to have health benefits, and some, such as ricin, can be a deadly poison upon consumption.[3] Putting them all under one umbrella is basically meaningless.

The main case against lectins comes from their biological activity. Lectins strongly and specifically bind to sugars (carbohydrates). This affinity for sugars is captured in the word "lectin" itself, which is derived from the Latin word legere, or "to select."[4] Lectins have been compared to keys that can unlock specific carbohydrates, which, in turn, can disrupt the cells in which they are housed and cause inflammation.[5]

If you consume certain lectins and do not have the enzymes to properly digest them, they can pass through the digestive tract undisturbed, which has been linked to nutrient deficiencies, disrupted digestion, and severe intestinal damage.[6] There are also proposed risks if lectins enter the body's circulation. Review articles based mostly on animal findings have posited that ingested lectins could increase intestinal permeability; get past the gut wall; and deposit themselves in distant organs, causing inflammatory conditions, such as rheumatoid arthritis and diabetes.[7,8]

Lectins' new status as a public health hazard is an unlikely turn of events, because they are found in foods generally considered the staple of a healthy diet—whole grains, beans, peas, tomatoes, nuts, milk, and fruit, to name a few. Lectin-containing foods could double as the shopping list of a health fanatic (Figure). This makes the prospect of avoiding lectins somewhat dubious.

Figure. High- and low-lectin foods.


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