This common nut can be healthy—or poisonous

By Alistair Gardiner
Published December 3, 2020

Key Takeaways

In many ways, cashews are the perfect snack. Cashew nuts—which are technically seeds—are packed with beneficial fatty acids, antioxidants, and proteins. Alongside a host of other nuts, cashews are considered an excellent source of nutrients, and their consumption has been linked to a number of health benefits, including lower cholesterol levels and a reduced risk of diabetes.

However, most people are unaware that raw, unprocessed cashews contain a number of harmful substances and toxins. So, what are these components? How dangerous are they? And how do you know when a cashew is safe to eat? This article will break down what makes up cashews and spotlight which elements benefit us, and which may do us harm. 

The nut that’s actually a seed

Cashews grow on a type of tropical evergreen tree called anacardium occidentale. What we think of as cashew nuts are actually seeds that grow inside a shell at the bottom of a cashew apple.

Cashew trees are part of the anacardiaceae family, which includes mango, poison ivy, sumac, pistachio, and Peruvian pepper. The mention of poison ivy among that list foreshadows one of the common characteristics of these plants—they all contain urushiol, an oil that is a potent skin irritant. 

Not only does the cashew nut shell oil contain urushiol, it includes a number of other harmful components, including anacardic acid, cardol, and cardanol. That’s why the cashews that we buy in the supermarket have been processed via several steps—to ensure they’re safe to eat. While there are variations on this process, it typically begins with several rounds of heating and cooling in order to extract the nut from the shell. Then the nuts are dried either in the sun or in a roaster to remove moisture. Following this, another roasting or steaming takes place to further ensure all nut shell liquids are removed. 

These substances are the reason that cashews are never sold in the shell and are most often roasted. That includes those labeled “raw” on a store shelf, which may be free of added flavoring or salt, but will always have been either steamed or roasted to get rid of urushiol. However, even cooked and treated cashews can still cause allergic reactions in some people—particularly those with sensitive immune systems. 

Bad reactions

While most store-bought cashews have been treated to ensure they’re safe, you may still have a bad reaction to cashews. Tree nut allergies are one of the eight most common food allergies, affecting up to 1% of the US population, according to the American Academy of Allergy, Asthma, and Immunology. One study, published in the journal Allergy, suggests that cashew nut allergies may be on the rise and that allergic reactions to cashews can be more severe than reactions to other tree nuts, and peanuts.  

If your skin came into contact with raw, unprocessed cashew nuts, or the nut shell oil, the urushiol would likely cause an irritable skin rash, similar to that inflicted by poison ivy. According to the American Academy of Dermatology, most people react in this way after exposure to urushiol. As such, workers responsible for shelling cashews try to avoid contact with the shell liquids.

Although cashew nut shell toxicity is getting more attention these days, the problem has been known for decades. The effect of urushiol exposure can be seen in a real-world case study from 1982. According to a report from the CDC, in April of that year, more than 7,500 bags of cashews that were contaminated by pieces of shell were sold in Pennsylvania and Maryland as part of a Little League fundraiser. The agency reported that 20% of those who purchased and ate the cashews experienced pruritic dermatitis, and concluded that high sensitivity to poison ivy appears to correlate with high sensitivity to cashew nut shell liquid.

Similarly, an animal study which sought to establish the effects of acute toxicity of cashew nut shell extract on rats found that it produced a variety of clinical symptoms and behavioral changes. These included scratching, twitching, tremors, writhing, and even death.

Overall, research suggests that your reaction to urushiol is highly dependent on the concentration to which you’re exposed and your allergic sensitivity to it. 

Cashews can boost health

All of that said, store-bought cashews are usually safe to eat, due to the process of heating and preparing them. In fact, as long as you’re not experiencing any allergic reactions, cashews can be a great addition to a balanced healthy diet. 

Studies have found evidence to support the idea that nut consumption is associated with a cardioprotective effect. One review found that the risk of coronary heart disease was 37% lower for those who eat nuts more than four times per week, compared with those who never or almost never consume nuts. 

Research also shows that incorporating cashews into your diet can have an impact on your cholesterol levels. One study found that the consumption of cashews was associated with a decrease in LDL cholesterol and total cholesterol, with the authors suggesting that substituting a high-carbohydrate snack of cashews could be an effective way to manage cholesterol.

Other research has shown that cashews can have a positive impact on those with type 2 diabetes. In a study published in the International Journal of Endocrinology and Metabolism, researchers started out with the assumption that the monounsaturated and polyunsaturated fatty acids present in cashews are the main reason the nut is associated with reduced risk of cardiovascular disease. The study sought to explore whether cashews had a similarly helpful impact on lipid profile and glycemic control. 

After monitoring a group of diabetic participants over the course of 8 weeks, the researchers found that the serum insulin and LDL-to-HDL cholesterol ratios had significantly decreased in the group consuming cashews. While further studies are required, the findings suggest that cashews could be beneficial for those suffering from diabetes. 

So, don’t be afraid of cashews—they can do a lot of good for your heart and general health. But there’s a chance that your body may not tolerate them, so pay attention to how you react after grabbing a handful for your next snack.

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