Can Peanuts Cause Cancer?

So today’s short post is about whether the staple of many a health (or unhealthy) individual’s snack box, the peanut, is cancer causing. This question peaked my interest when I read about aflatoxin, a natural toxin produced by certain strains of mold. Aflatoxin it turns out, can be rife in peanuts. As I am a tad partial to a spoonful of peanut butter here and there, this left me feeling a tad bit worried. Time for a little further investigation..

So our offending culprit Aflatoxin, is also known as Aspergillus flavus and A. parasiticus. Aflatoxin is reported to be a no less than a ‘potent’ carcinogen and is known to cause liver damage (!). If an animal is exposed to aflatoxin in great amounts or over a long period of time, it can cause liver failure and liver cancer. Aflatoxin consumption has also been shown to stunt growth in children.

People can be exposed to aflatoxins by eating contaminated plant products (such as peanuts) or by consuming meat or dairy products from animals that ate contaminated feed.

Peanuts grow underground which can be the perfect breeding ground for these molds. As part of their life cycle, molds produce and excrete various substances, and these strains excrete aflatoxin.

Similarly, when stored in warm humid silos for periods of time, peanuts can also become contaminated. Peanuts aren’t the only affected crops either. Aflatoxins have been found in pecans, pistachios and walnuts, as well as milk, grains, soybeans and spices.

If the infected peanuts are made into a product such as raw peanut butter, the aflatoxin also becomes part of the product.

Are we protected?

Roasting kills about 50 percent of the aflatoxins present in nuts. Additional to this, hand sorting after roasting to remove discoloured/rancid looking nuts further reduces the number of contaminated nuts that make it to market, according to the International Food Safety Network.

There are limits on the level of aflatoxins that can be in foods imported into the UK and the rest of the European Union (EU) and some products might need to be tested. It seems a little unclear from what I’ve read however as to how this checking takes place.

A few years ago, Consumers Union , an organisation in the United States, looked into aflatoxins in peanut butter. They found that the amounts detectable varied from brand to brand. The lowest amounts were actually found in the big supermarket brands and the highest levels were found in peanut butter ground fresh in health food stores.

This is probably as processing peanuts through heating, roasting, boiling, or pasteurising the peanut product can reduce the molds, which are killed by high heat, and thus reduce potential aflatoxin exposure.

Staying safe

So although it’s (somewhat) reassuring that there is government and industry recognition of this issue, like most things, your own preventive measures can be put in place to better reduce the risk.

Firstly, I’d say that home made nut butters are generally a far healthier option anyway, as you can be sure they don’t include hidden nasties such as sugars and vegetable oils. When making nut butters though, ensure you roast your nuts, (sorry), first. Also look through fresh peanuts, removing any wrinkled and shrivelled ones.

Also remember to always refrigerate your peanut butter to prevent aflatoxin from growing in potentially warm humid conditions in your kitchen. Lastly, and a bit randomly, eat ellagic acid, that can be found in strawberries, grapes and raspberries. This is as ellagic acid has been found to protect against aflatoxin in the body.


Anyone eating peanuts, peanut butter, and peanut products, whether raw or cooked, may take in a little aflatoxin. The point is not to be scared of eating raw peanuts or peanuts in general but to avoid long-term or high levels of exposure. Eating a handful of raw peanuts a few times a week probably won’t expose your body to enough aflatoxin to cause ill effects; eating raw peanut butter three times a day for years may. Till next time.

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