Gary from Carmel, California, writes, "You have helped me out in the past so I thought I'd get your opinion on this. On a recent show, a doctor was talking about which foods to eat and which to avoid. He said that you should be eating nuts, but don't eat cashews, as they are not a nut but rather a seed and contain high levels of lectin. I always thought that cashews were a tree nut just like walnuts, etc. Can you shed some light on this for me?"
In this case, I'm afraid my opinion would not be worth much. I needed the expertise of horticulturist Pat Regan, who humbly describes himself as "a friend who spends a lot of time pondering plant parts and identification."
Pat explains that the names we commonly use often distort the scientific terms for plant parts. "Fruit" and "vegetable" are typically considered the worst-abused, but "nut" probably comes in first place, he says.
"All true nuts are seeds, but not all seeds are nuts," Pat says.
Kind of like all trees are plants but not all plants are trees?
So ... a nut is a type of seed. Got it.
"Botanically," he continues, "a nut is a dry fruit with one seed and a thick hard shell. Think of acorns, hazelnuts, chestnuts or hickory nuts. On the other hand, cashews come from a fleshy fruit, not a hard shell. They are more like plums, apricots, cherries and olives."
Cashews, says the Integrative Medicine Department at the University of California-Davis, are technically not a nut. Although they grow on trees, they are really seeds that grow from a strange-looking fruit called a cashew apple.
"Incidentally," Pat continues, "peanuts (a legume), walnuts, almonds and pecans are not true (botanical) nuts, either. Nor are pine nuts, pistachio nuts and brazil nuts, and yet most would call me a nut for saying so."
As for lectins, these are proteins that occur naturally in most raw plants, including cashews. The good news is that cooking destroys the activity of these proteins — one reason why cashews are always sold roasted or steamed.
The other reason is that raw cashews are enclosed in a shell that contains a resin called urushiol, the same rash-causing substance found in poison ivy. Heat inactivates urushiol — another reason cashews are always sold shelled and roasted or steamed.
One last word about nuts in general, including the "not true nuts." They are a good source of protein, micronutrients, healthful fats and disease-fighting antioxidants. And according to the Micronutrient Information Center at Oregon State University, consuming a variety of nuts on a regular basis is associated with a lower risk for heart disease and Type 2 diabetes.
To which Pat adds, "It does not sound like eating cashew seeds is such a bad idea." Thank you, friend.
Barbara Quinn is a registered dietitian. Email her at firstname.lastname@example.org.
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