Aflatoxin in Nuts (and How to Reduce Your Exposure)

All nuts are susceptible to contamination by aflatoxins, harmful substances that are produced by certain naturally occuring fungi such as Aspergillus flavus and Aspergillus parasiticus. Not only are aflatoxins known to cause cancer, they have also been linked to impaired immune function, nutrient deficiencies, gastrointestinal problems, and stunted growth in children. Ingestion of nuts that contain high levels of aflatoxins may also lead to acute aflatoxin poisoning which may cause abdominal pain, vomiting, excess fluid in the lungs, fatty liver, and necrosis of the liver.

On the other hand, nuts also have many health benefits, and it makes no sense to avoid nuts just because they may contain aflatoxins. What's more, the risk of acute aflatoxin poisoning in developed countries is very low because government regulators in these countries have established food safety guidelines and regulations to control the amounts of aflatoxins in nuts and other foods.

The U.S. Food and Drug Administration, for example, has set the maximum acceptable level of aflatoxins at 20 parts per billion (ppb) for all foods, including nuts and nut butters (1). This limit applies for both organic and non-organic nuts and nut butters.

In the member states of the European Union, the maximum level of aflatoxin allowed to be present in nuts depends on the type of nut or nut product: For example, ready-to-eat pistachios, almonds and nut butters are allowed to contain up to 10 mcg/kg (10 ppb) of total aflatoxins and 8 mcg/kg (8 ppb) of aflatoxin B1. In Brazil nut and hazelnuts, the maximum level is 10 mcg/kg (10 ppb) for total aflatoxins and 5 mcg/kg (5 ppb) for aflatoxin B1. And, one kilogram of peanuts, cashew nuts, walnuts, macadamia nuts or pecans is allowed to contain only 4 mcg/kg (4 ppb) of total aflatoxins and 2 mcg/kg (2 ppb) of aflatoxin B1. The European Commission has set separate limits for aflatoxin B1 because this type of aflatoxin is considered to be particularly dangerous. (2)

Read on to learn more about aflatoxin levels in different nuts and to get tips on how you can reduce your exposure to these toxic compounds.

Peanuts

When it comes to foods that appear to be particularly prone to aflatoxin contamination, peanuts are right there on top of the list. In fact, despite the FDA's best efforts to keep the amount of aflatoxins in peanuts and peanut butter below dangerous levels, there have been several recalls resulting from peanut butter products containing aflatoxin above the allowable limits in the US (3). To reduce your exposure to aflatoxins from peanuts, only buy high-quality peanuts and peanut butter that look and taste good, and store your peanuts in a dry, cool place. What's more, if you like the flavor of freshly-ground peanut butter, you may want to get a food processor or blender suitable for making nut butters, and start making your own peanut butter. The grind-your-own peanut butter machines you see in health food stores can easily become contaminated with aflatoxins if the machines are not thoroughly cleaned and the peanuts are allowed to sit in them for a long period of time.

Pistachios

Among tree nuts, pistachios seem to be particularly susceptible to contamination by aflatoxins, particularly aflatoxin B1. A large Japanese study that looked at the aflatoxin levels in over 3,000 samples of foods or foodstuffs, including cereals, nuts, beans, spices, dairy products and dried fruits, found that pistachios had the highest levels of aflatoxin B1 among the tested products (4). In another study, Qatari researchers analyzed the aflatoxin levels in pistachios and a number of other nuts including peanuts, cashews, walnuts and hazelnuts. They analyzed 81 nut samples in total, but aflatoxins were only detected in pistachios and peanuts. They also found that pistachios without shell contained higher levels of aflatoxins than unshelled pistachios. (5)

Brazil Nuts

Brazil nuts have numerous health benefits, many of which have been linked to their exceptionally high levels of selenium. One of the most famous potential health benefits of selenium is its ability to reduce the risk of certain types of cancer (6). But, just like all other nuts, Brazil nuts may sometimes become contaminated with aflatoxins, which may negate some of the beneficial effects of selenium. To reduce your risk of ingesting aflatoxin-contaminated Brazil nuts, look for properly stored, undamaged Brazil nuts. It is also worth noting that in-shell Brazil nuts have been found to contain lower levels of aflatoxins than their shelled counterparts.

Cashews

Cashews do not seem to be as susceptible to aflatoxin contamination as many other nuts. The Canadian 2010-2011 Aflatoxin Survey, which analyzed 250 samples of nuts and nut butters, found aflatoxins in several types of nuts, including Brazil nuts, walnuts and peanuts, but no detectable levels in cashews (7). Also another large-scale study, conducted in Cyprus in the 1990s, found no aflatoxins in cashews (8). In yet another study, researchers collected 90 nut samples from a local market in Tripoli, Libya, and found that among the tested nuts, cashews had the lowest incidence of aflatoxin contamination: only 13 percent of the cashew samples contained detectable levels of aflatoxins. (9)

Sources:
1. Guidance for Industry: Action Levels for Poisonous or Deleterious Substances in Human Food and Animal Feed. U.S. Food and Drug Administration Last accessed: January 2018.
2. EU Commission Regulation (EC) No 1881/2006 of 19 December 2006 setting maximum levels for certain contaminants in foodstuffs, amended by Commission Regulation (EU) No 165/2010 published on February 27, 2010.
3. M. Palumbo et al (2017). Recalls of tree nuts and peanuts in the U.S., 2001 to present [Table and references]. UC Davis.
4. Tabata et al (1993). Aflatoxin contamination in foods and foodstuffs in Tokyo: 1986-1990. Journal of AOAC International, 76(1):32-5.
5. A. Abdulkadar et al (). Aflatoxin contamination in edible nuts imported in Qatar. Food Control, 11(2), 157-160.
6. M. Rayman (2005). Selenium in cancer prevention: a review of the evidence and mechanism of action. The Proceedings of the Nutrition Society, 64(4):527-42.
7. 2010-2011 Aflatoxins in Dried Fruits, Nuts and Nut Products, and Corn Products. Canadian Food Inspection Agency. Last accessed: January 2018.
8. E. Ioannou-Kakouri et al (1999). Surveillance and control of aflatoxins B1, B2, G1, G2, and M1 in foodstuffs in the Republic of Cyprus: 1992-1996. Journal of AOAC International, 82(4):883-92.
9. N. Essawet et al (2017). Natural Incidence of Aflatoxins and Ochratoxin A Nuts Collected from Local Market in Tripoli. International Journal of Current Microbiology and Applied Sciences, 6(3), 1479-1486.