What is cashew?

Cashew is the seed of Anacardium occidentale, an evergreen tree of the tropics. It is sold as a snack nut, a butter, a milk and a sauce thickener. In Haiti it is nwa kajou; the swollen fruit stalk is pomme cajou.

That stalk is a soft, juicy false fruit called the cashew apple. Dominicans call the tree marañón, and in Cuba it is cajuil. The apple is pressed for juice or boiled into jam.

One hazard comes before anything else. The shell around the raw seed holds a caustic oil. It blisters skin and mouth much like poison ivy, a close plant relative.

Every cashew sold as food has been steamed or roasted to drive that oil off. Shelling cashews is a job for gloves and training, not a home kitchen. Cashew is also one of the most common causes of severe nut allergy.

Caribbean households have long used more than the kernel. Leaf teas, bark decoctions and the apple juice all have a place in home practice. Long use is not proof that a remedy works, and it is not proof that it is safe.

Here is the short verdict. Eating cashew nuts has small, measured effects on blood fats and blood pressure. The leaf and bark remedies rest on lab and animal work, with almost no human testing.

How does cashew work?

Cashew nuts are mostly fat, and most of that fat is unsaturated. Diets higher in these fats are linked to small drops in triglycerides, a type of blood fat. That link has been measured in people, not only in cells.

The nuts also carry magnesium, fibre, protein and plant sterols. Each of these is thought to play some part in the blood pressure and blood fat findings. How much each one adds is not settled.

Leaf and bark teas are a different story. In test tubes and in animals, the extracts slow some bacteria. They also slow gut enzymes that release sugar from starch.

Whether any of that happens in a person who drinks the tea has not been shown. The tannins in the leaf are astringent, meaning they tighten tissue and taste drying. That is the likely reason the tea was used for loose stools and sore gums.

Cashew apple juice is high in vitamin C. Vitamin C prevents and treats scurvy, and that effect is proven. It does not make the juice a treatment for anything else.

The shell oil works by irritation. It is chemically close to urushiol, the compound in poison ivy. Rubbing it on a wart or corn burns healthy skin as well, which is why that old practice is unsafe.

What forms does cashew come in?

Most people meet cashew as a food, and that is the form with the best evidence behind it.

Common food forms: roasted kernels, salted or unsalted; cashew butter; cashew milk; cashew-based cheese and cream; cashew flour.

Cashews labelled raw are not truly raw. They have been steamed or roasted to remove the shell oil. Truly raw in-shell cashews are not sold as food.

Caribbean home forms: cashew apple juice, jam and wine; leaf tea; bark decoction used as a mouth rinse or drink.

Supplement forms: cashew leaf extract capsules exist online. They are not standardised, and there is no human trial behind them.

Industrial form: cashew nut shell liquid, used in brake linings, resins and paints. It is not a consumer product and has no place in home remedies.

Where it comes from:

Cashew is not originally Caribbean. The tree comes from north-east Brazil, where Indigenous Tupi people used the apple and the nut long before contact. Portuguese and Spanish ships carried it through the islands and on to Africa and India in the 1500s.

Once settled in the Caribbean, it entered household practice fast. Leaf and bark teas were taken for loose stools, sore gums and toothache. Bark decoctions were also drunk for what people called sugar sickness.

The apple was used differently. Its juice was given for colds, sore throat and as a refreshing tonic in heat. Healers in Haiti, Cuba and the Dominican Republic all recorded versions of these uses.

The shell oil had its own grim reputation. It was dabbed on warts, corns and ringworm, and it was known to burn. That practice caused real injuries and should not be copied.

These records tell you what people did and valued. They are not a measure of whether the remedies worked.

What does cashew help with?

• Blood fats, including triglycerides: This is the strongest claim, and it is still a modest one. Short feeding trials show cashew nuts lower triglycerides a little. LDL cholesterol barely moves. The trials were small and ran only weeks. Cashews are a reasonable swap for crisps or sweets. They are not a treatment for high cholesterol.
• Mild blood pressure support as part of diet: Several trials report a small drop in the top blood pressure number. The size is a few points, not a dramatic fall. Salted cashews may cancel that out, since salt raises blood pressure. Keep taking any medicine your doctor has prescribed.
• Diet quality in type 2 diabetes: A 12-week trial in India gave adults with type 2 diabetes a daily portion of cashews. Blood sugar and weight did not get worse, and blood pressure fell slightly. That is a useful finding, but it is not a sugar-lowering effect. Cashews fit a diabetes diet; they do not treat it.
• Loose stools (traditional use): Caribbean practice used leaf and bark tea for diarrhoea. The tannins in the leaf are astringent, which may explain the appeal. No human trial has tested it. Diarrhoea with blood, fever or signs of dehydration needs medical care, not tea.
• Sore gums and mouth ulcers (traditional use): Bark and leaf washes were used as mouth rinses for sore gums and toothache. In lab tests, extracts slow some mouth bacteria. Whether this helps a real mouth is not established. Toothache usually has a cause that only a dentist can fix.
• Colds and low vitamin C (cashew apple juice): The apple juice is genuinely rich in vitamin C. Vitamin C prevents and treats scurvy, a proven effect. It does not prevent or shorten colds in any clear way. Drink it because it is pleasant and nourishing, not as a cold cure.
• Warts and corns (traditional, unsafe): Shell oil was once dabbed on warts, corns and ringworm. It does destroy tissue, because it is caustic. It destroys healthy skin too, and causes blisters, scarring and infection. Do not use it. Safe wart treatments are sold in any pharmacy.

Which foods are rich in cashew?

1. Roasted cashew nuts
2. Cashew butter
3. Cashew milk and cashew cream
4. Cashew-based vegan cheese
5. Cashew apple juice and jam (cajuil, marañón)
6. Indian and Thai curry sauces thickened with cashew
7. Trail mixes and nut bars

Practical Tips:

Cashew hides in a lot of prepared food. Vegan cheeses, creamy curry sauces, pesto and nut bars often contain it.

If you are allergic, read labels every time. In the US, UK, EU, Canada and Australia, packaged foods must declare cashew.

Restaurant food is the harder problem. Ask directly about sauces and desserts before you order.

What are the side effects of cashew?

• Allergic reaction, from itchy mouth to life-threatening anaphylaxis
• Hives, swelling of the lips, tongue or throat
• Blistering skin rash after contact with shells or poorly roasted nuts
• Bloating, wind or loose stools from the fat and fibre
• Weight gain if large amounts are eaten on top of a usual diet
• Too much salt from heavily salted packs
• Added risk of calcium oxalate kidney stones in people prone to them
• Choking, in children under about four years

Good to know:

For most people, roasted cashews are a well-tolerated everyday food. Upset stomach and wind are the usual minor complaints.

The serious risk is allergy. Cashew allergy is common, often severe, and can begin in childhood or in adulthood. Reactions can involve breathing and blood pressure, not just the skin.

The other serious risk is contact with the shell. Shell oil causes chemical burns and blistering rashes. Poorly processed nuts have caused the same reaction.

Leaf and bark teas have no safety record in people. Unknown is not the same as safe.

How much cashew should you take?

• Recommended daily: Nothing here is personal advice. Ask your own doctor or dietitian about amounts. Food labels treat one serving of cashews as about 28 g. That is roughly a small handful, or 15 to 18 kernels. Human trials have generally used about 28 to 60 g a day. No sound amount can be given for cashew leaf or bark tea. Strength varies hugely between batches. No human study has set an amount that is known to be safe or useful. Cashew nut shell oil has no safe home amount at all. It is caustic. Keep it off skin and out of food and drink.
• Best time of day: Time of day does not appear to matter. No study has compared morning and evening intake. Many people use cashews as an afternoon snack or in cooking. Pick whatever fits your routine.
• With or without food: Cashews are a food, so this question matters less than usual. Eat them on their own or in a meal. One timing point is worth knowing. Minerals in nuts can bind some tablets in the gut. If you take thyroid medicine or certain antibiotics, leave a few hours between the pill and a large nut snack.
• Time to effect: Expect slow and small, if anything at all. Trials measured changes in blood fats and blood pressure only after 8 to 12 weeks. Most people will feel nothing. These are numbers on a test, not sensations. Vitamin C from cashew apple juice is the exception. In true vitamin C deficiency, symptoms start to improve within days.
• How long to take it: As a food, cashews can be part of a normal diet for life. There is no reason to cycle them on and off. The trials that measured blood fats and blood pressure ran 8 to 12 weeks. Longer effects have not been well studied. For leaf or bark tea, no safe length of use can be named. Nobody has tested daily use over weeks or months in people.