Ron from Corvallis, Oregon, writes this in response to a recent column on lectins: “I am a biochemist (and) used to work with immunologists at Sloan Kettering. The main reason I'm writing is to ask you to explore the toxicity of nuts' lectins and the best way to prepare nuts without getting sick. My wife loves pecans; I am fondest of cashews and pistachios.
I'm interested in the chemistry and physiology of the lectins, but I doubt most readers would be.”
Well, Ron, it may be easier to talk about the chemistry of lectins than your main question. That’s because there is very little research about the lectin content of nuts — or if they are even a problem.
A recent review article in the journal Nutrients states that lectins are widely distributed throughout the plant kingdom (more than 500 different types have been identified). In their active state, lectins can interfere with the absorption of nutrients and — according to some animal research — may even play a role in triggering digestive and other diseases.
On the other hand, certain lectins are now being studied for their therapeutic benefits, most specifically to diagnose and treat cancer. And so the paradox.
According to research via Blue Zones, lectins are found in all plants, a protein that helps them thrive and survive.
"The same characteristics that protect them in nature can lead to digestive discomfort if consumed by humans — but there’s a catch," the research continues. "Lectins are in all plants. Plants that we’ve been eating for thousands of years, like rice, wheat, potatoes, tomatoes, seeds, nuts, but the highest amounts are found in raw legumes (beans, lentils, soybeans, peas, and peanuts included) and whole grains...
Avoiding lectins altogether would mean avoiding almost all plant foods, which would mean avoiding a majority of the foods that the longest-lived people in the world consumed every day of their lives as well as the foods shown to reduce risk of chronic diseases like heart disease and diabetes.”
So Ron, although I couldn’t find data about the exact content of lectins in nuts, here’s the good news about your favorites. They are all heated, cooked or dried after harvest, which experts say can reduce or eliminate the activity of lectins.
Pecans are heated in a 180 F water bath as part of processing. Although pistachios can be eaten raw, most commercial pistachios are heat dried before being packaged. And cashews are never sold raw. They have to be cooked, roasted or steamed to remove a toxic oil in the shell that can irritate the skin like poison ivy.
At this point, I’d say the evidence for the health effects of nuts far outweigh the threat of lectins, especially if we eat roasted or otherwise cooked products. Thanks for stretching my brain this week.
Barbara Quinn is a registered dietitian. Email her at email@example.com.