A seemingly harmless habit—eating peanut butter on toast every morning—led to a shocking diagnosis for a woman. Despite being in good health, not drinking alcohol, and having no history of hepatitis B or C, she was diagnosed with liver cancer, with a large tumor already metastasized to her lungs.

Dr. Liu Boren, a functional medicine and nutrition specialist from Taiwan, shared the case of this patient. She had been experiencing digestive discomfort and sought medical evaluation, only to be stunned by the diagnosis. Upon further investigation, it was discovered that she had eaten peanut butter on toast every morning for 20 years. Dr. Liu suspected that the prolonged consumption of peanut butter contaminated with aflatoxin could be the cause of her liver cancer.

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Understanding the Risk: Aflatoxin in Peanut Products

Peanut butter’s main ingredient is peanuts, often referred to as “longevity nuts” due to their beneficial unsaturated fats, which can reduce the risk of heart disease. However, peanuts, corn, and other crops are highly susceptible to contamination by aflatoxin—a potent carcinogen classified as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC) under the World Health Organization (WHO). Aflatoxin exposure is strongly associated with liver cancer and may also contribute to kidney and stomach cancers.

Aflatoxin is produced when peanuts or other starchy foods are exposed to high humidity or heat and become moldy, allowing Aspergillus species to thrive. Many people assume that simply removing moldy parts or washing the peanuts or corn is enough, but aflatoxin is a chemical compound that cannot be eliminated through ordinary cooking or boiling at 100°C. Scientific studies show that aflatoxin is only partially destroyed at extremely high temperatures, typically above 150–200°C, such as during industrial roasting.

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How to Safely Consume Peanut Products

To minimize risk, it is important to purchase peanut butter and related products from trusted sources with clear labeling and quality assurance. Avoid peanut butter that has hardened, smells sour, or shows discoloration, as these are signs of spoilage and potential aflatoxin contamination.

While some commercial processing methods can reduce aflatoxin levels by up to 89%, prolonged consumption of contaminated products—even in small amounts—can accumulate over time and pose a serious health risk.

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Other Foods Prone to Aflatoxin Contamination

Aflatoxin is not limited to peanuts. Other common foods that can be contaminated include:

• Bitter or moldy seeds: Sunflower seeds and other nuts that taste unusually bitter may contain aflatoxin. If you eat them, spit them out immediately and rinse your mouth thoroughly.

• Improperly stored wood ear mushrooms: Known as black fungus, these mushrooms are rich in protein and cellulose. If soaked or stored incorrectly for a long time, they can develop mold, turning yellow, black, or grayish, producing aflatoxin. Soaking water may appear foamy, cloudy, and have a strange odor.

• Moldy rice or fruits: Rice is a staple food rich in starch, making it susceptible to mold during harvest and storage. Moldy rice, if not removed, can introduce aflatoxin into meals. Cooking at regular boiling temperatures does not completely destroy this toxin. Similarly, moldy fruits can pose a similar risk.

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Key Takeaways

• Avoid consuming visibly moldy or spoiled foods, including peanuts, corn, rice, and dried mushrooms.

• Purchase peanut butter and other nut products from reputable brands.

• Regularly check storage conditions for nuts and grains to reduce moisture and prevent mold growth.

• Be aware that aflatoxin is heat-resistant and can remain even after normal cooking, so prevention is critical.

Even foods commonly considered healthy, such as peanuts, can pose hidden dangers if contaminated with aflatoxin over long periods. Awareness and careful food selection are essential to prevent potential health risks, including liver cancer.