Should We Worry About Mycotoxins in Oats?

There is a growing concern that oats, a staple food in many homes, contain mold-produced substances called mycotoxins. But are they actually a health concern and a reason to quit oats? Two doctors weigh in.

Molds are a type of fungi primarily found in the natural environment but they can also thrive indoors with high humidity. Airborne molds are often blamed for a range of health issues, including a widely debunked toxic mold syndrome.

However, most molds in the air aren't harmful to humans, except for some types that may trigger allergic reactions and asthma.

Mycotoxins, on the other hand, have been associated with more severe risks when ingested with foods like crops, nuts, and spices.

Some wellness influencers, often those who endorse low-carbohydrate diets, warn against eating oats and oatmeal, citing concerns over mycotoxins. But should you remove them from your diet?

Ochratoxin A in breakfast cereal

Multiple studies found mycotoxins in breakfast cereals sold worldwide, and the United States is no exception.

According to a 2014 study, 75 of the 144 breakfast cereal samples tested contained a mycotoxin called Ochratoxin A (OTA). However, only 10 products, all made of oats, exceeded the maximum OTA limits of 3 ng/g set by the European Commission.

A larger study that tested 489 samples of breakfast cereals from retail marketplaces in the U.S. found that 205 samples (42%) were contaminated with OTA. Similarly, only a small fraction – 16 samples of oat-based cereals – were above the European Commission standard.

In animals, exposure to Ochratoxin A via food has been associated with developmental anomalies and birth defects, as well as adverse effects on the immune system, liver damage, and kidney function.

The International Agency for Research on Cancer classifies OTA as a possible human carcinogen due to associations with mammary gland, kidney, and liver tumors in mice.

The findings in animal models are important for understanding the potential risks of mycotoxins, but does it mean Ochratoxin A is equally toxic to humans?

A comprehensive review of OTA's role in cancer development published in 2024 concluded that the results of Ochratoxin A studies conducted in animals may not be fully representative of humans due to significant differences between species. For example, the mycotoxin may affect different organs in humans and animals. The specific mechanism responsible for tumor development wasn't identified either.

The review echoed the 2017 risk assessment, suggesting that Ochratoxin A doesn't pose a significant risk of adverse effects in Americans who consume most foodstuffs containing OTA.

Aflatoxins and cancer

While mycotoxins like Ochratoxin A don't appear to pose a significant risk to humans, the most poisonous ones, Aflatoxins, are categorized as a Group 1 carcinogen, along with tobacco smoking, ultraviolet radiation, and alcohol.

The US has stringent Aflatoxin regulations and inspections in place to help prevent contamination of food products.

In some parts of the world – Africa, rural China, and Southeast Asia – Aflatoxins are a serious health issue as they cause about 23% of liver cancer cases.

According to the WHO, ingesting large amounts of Aflatoxins can lead to acute poisoning, which can be life-threatening, usually through damage to the liver. It has also been shown to damage DNA and cause cancer in animals.

Austin Shuxiao, MD, says Aflatoxin-producing molds typically do not grow well on oats, and studies found only trace levels of the mycotoxin in oats.

Liver cancer risk from exposure to Aflatoxins is higher if there is a co-infection with hepatitis B or C virus.

Luckily, in developed countries, especially ones with hepatitis B vaccinations like the US, the direct risk is low and typically negligible.

Austin Shuxiao, MD

Oats rarely exceed 2ng/g of aflatoxin B1 (AFB1), so a 50 g serving would produce 0.1 ug of AFB1.

Shuxiao says that consuming 50 g of oats daily – about four tablespoons of raw oats or about 150-200 g of cooked oats – would result in about 0.013 liver cancer cases per 100,000 people without hepatitis B virus (HBV) per year.

In HBV-positive people, the same consumption of oats would lead to around 0.42 liver cancer cases per 100,000 people per year.

Deoxynivalenol and GI effects

Another mycotoxin, Deoxynivalenol (DON), is nicknamed 'vomitoxin' due to its ability to induce vomiting, nausea, and diarrhea, Shuxiao explains. Exposure to DON comes from improperly stored oats, as well as wheat and maize.

Mycotoxins T2 and HT-2 are highly toxic and, when ingested with moldy grain, may cause alimentary toxic aleukia, which is a fatal hemorrhagic disease in people. According to the Food and Drug Administration (FDA), these toxins can also cause high fever and gastrointestinal symptoms.

However, Shuxiao says he has never encountered individuals who suffered from illnesses caused by these mycotoxins, likely because they are uncommon due to modern grain storage techniques and regulations.

Should I stop eating oats because of mycotoxins?

Shuxiao says he wouldn't stop eating oats for fear of mycotoxins.

Oats are rich in beta-glucan, a fiber that has been proven to lower LDL cholesterol, the so-called 'bad' cholesterol. Consuming 1.5 cups of oatmeal a day provides around 3 g of beta-glucan, which can reduce LDL levels by 5-10%.

That can significantly lower your cardiovascular risk profile. Oatmeal also has a low-moderate glycemic index and stabilized postprandial blood glucose and should be recommended for anyone with type 2 diabetes or metabolic syndrome.

Austin Shuxiao, MD

Oats are rich in vitamin B1, thiamin, and manganese while being low in calories.

A 2019 review of evidence concluded that phytonutrients in whole grains may have protective effects against contaminants, including mycotoxins.

Phytonutrients, also called antioxidants, are natural compounds found in plants that play a role in the prevention of many diseases, including diabetes, obesity, and cardiovascular diseases.

"The consumer is best protected by eating a healthy balanced diet, rich in nutrient-dense foods, including wholegrain options," the authors concluded.

According to Daniel Atkinson, MD, because oats are nutritionally dense foods packed with various vitamins and fiber, the benefits far outweigh the unlikely potential risks of mycotoxin poisoning.

Mycotoxin contamination is not exclusive to grains like oats. These substances can be also found in meat, dairy products, and even wine.

Do organic oats contain less mycotoxins?

If you're still worried about mycotoxins, can opting for organic oats be a way to reduce the potential exposure?

A 2016 review of evidence comparing the content of various mycotoxins in conventionally and organically produced grains found that most studies didn't find significant differences in DON content in cereals from the two farming systems. However, some studies showed lower DON levels in organic cereals.

Many authors suggested that weather conditions, years, locations, tillage practice, and crop rotation are more important for the development of DON than the type of farming.

According to the review, organically produced oats contained mainly lower levels of T-2 and HT-2 toxins than those conventionally produced.

Meanwhile, most studies on zearalenone (ZEA) reported no differences between farming systems or lower concentrations in organically produced grain.

The takeaway

Mycotoxins like Ochratoxin A can be found in oat cereals and other grain products sold in the US. However, their amounts are usually too small to cause health concerns. As for more dangerous mycotoxins like Aflatoxins, stringent regulations are effective at keeping them from the food chain.