Potential Risks of Fermented Foods: What to Watch Out For

Fermented foods – from yogurt and kimchi to sauerkraut and miso – are widely celebrated for their gut-friendly benefits and rich flavours. But fermentation is not without its downsides. The same microbial activity that creates beneficial compounds can also produce substances that are potentially harmful to human health. Understanding these risks is essential for anyone involved in food science, food processing, or even home fermentation. This post breaks down the key harmful effects associated with fermented foods, focusing on biogenic amines, D(-) lactic acid, and other safety concerns you should know about.

What are biogenic amines and why do they matter? 🔗

Biogenic amines (BAs) are low-molecular-weight nitrogen-containing compounds that form when bacteria break down amino acids during fermentation. The main biogenic amines found in fermented foods include histamine, tyramine, phenylethylamine, putrescine, cadaverine, spermidine, and spermine. These compounds are produced through the action of microbial amino acid decarboxylase enzymes, which are commonly present in spoilage organisms as well as in lactic acid bacteria used in fermentation.

In small amounts, biogenic amines are not a problem. The human body has enzymes – specifically monoamine oxidase (MAO) and diamine oxidase (DAO) – that break down and detoxify these compounds in the intestine. However, when fermented foods contain unusually high concentrations of BAs, or when a person’s detoxification capacity is compromised, these amines can trigger a range of adverse health effects.

Health effects of specific biogenic amines 🔗

Histamine toxicity 🔗

Histamine is the most well-studied biogenic amine in the context of food safety. When consumed in excess, it can cause symptoms that closely resemble an allergic reaction – nausea, headache, skin flushing, respiratory distress, heart palpitations, diarrhoea, and changes in blood pressure. This condition is often called histamine poisoning or, in the case of fish products, “scombroid poisoning.” The European Food Safety Authority (EFSA) has stated that approximately 50 mg of histamine per meal is considered safe for a healthy individual. However, people with histamine intolerance – a condition where DAO enzyme activity is reduced – may react to much lower amounts.

Fermented fish, aged cheeses, sauerkraut, and fermented soy products are among the foods most likely to contain elevated histamine levels. Notably, some species of lactic acid bacteria (LAB) used in food fermentation can themselves produce biogenic amines, even though LAB are generally considered safe organisms.

Tyramine and hypertensive crisis 🔗

Tyramine is another biogenic amine commonly found in fermented and aged foods such as cheese, cured meats, and fermented soybean products. In healthy individuals, tyramine is efficiently metabolised by MAO enzymes. But for people taking monoamine oxidase inhibitor (MAOI) medications – a class of antidepressants – tyramine can accumulate in the bloodstream and cause a sudden, dangerous spike in blood pressure known as a hypertensive crisis. This reaction is sometimes referred to as the “cheese reaction” because aged cheese is a primary dietary source of tyramine.

Symptoms of tyramine toxicity include severe headache, rapid heartbeat, nausea, vomiting, and in serious cases, stroke.

Putrescine, cadaverine, and their role 🔗

Putrescine and cadaverine are biogenic amines that, while less directly toxic on their own, play a significant role in amplifying the effects of histamine and tyramine. These compounds can inhibit the enzymes responsible for breaking down histamine and tyramine in the human body. This means that even moderate amounts of histamine or tyramine become more dangerous when putrescine and cadaverine are also present in the same food.

Additionally, spermidine and spermine – two other biogenic amines – are known precursors of nitrosamines, which are compounds with potential carcinogenic properties. This adds another layer of concern to the long-term safety of foods with consistently high biogenic amine content.

Who is most vulnerable to biogenic amine reactions? 🔗

Not everyone reacts to biogenic amines in the same way. Several factors determine an individual’s susceptibility:

Individual enzyme activity: People with low levels of DAO or MAO – whether due to genetics, gut conditions, or medication – are at higher risk. Alcohol consumption: Alcohol inhibits the activity of amine-degrading enzymes, which is why consuming fermented or aged foods along with alcoholic beverages significantly increases the risk of biogenic amine toxicity. Medications: Beyond MAOIs, several other drugs used in hospital and clinical settings can suppress diamine oxidase function. Gastrointestinal conditions: People with inflammatory bowel disease, leaky gut, or other intestinal disorders may have impaired amine detoxification capacity.

Research suggests that biogenic amine toxicity can occur at levels a hundred times lower than the regulatory thresholds in sensitive individuals – a fact that makes personal health context extremely important.

D(-) lactic acid: a lesser-known risk 🔗

While biogenic amines get most of the attention, the production of D(-) lactic acid during fermentation is another important health concern. To understand this, you need to know that lactic acid exists in two mirror-image forms: L(+) lactic acid and D(-) lactic acid. The human body naturally produces and efficiently metabolises L(+) lactic acid. D(-) lactic acid, on the other hand, is metabolised much more slowly because the primary enzyme responsible – D-2-hydroxy acid dehydrogenase (D-2-HDH) – has limited activity in humans and is further inhibited under acidic conditions.

Certain lactic acid bacteria used in fermentation – including strains of Lactobacillus acidophilus, L. delbrueckii, L. fermentum, and L. plantarum – can produce D(-) lactic acid as a fermentation byproduct. Fermented foods like yogurt, pickles, sauerkraut, and sour milk products may contain this form of lactic acid.

D-lactic acidosis 🔗

When D(-) lactic acid accumulates in the blood faster than the body can clear it, it leads to a condition called D-lactic acidosis. This is most commonly reported in patients with short bowel syndrome (SBS), where unabsorbed carbohydrates reach the colon and serve as a substrate for bacterial production of D-lactic acid. The acidic environment created by D-lactate production then promotes the growth of more acid-resistant bacteria, creating a vicious cycle of escalating D-lactate production.

Symptoms of D-lactic acidosis include confusion, slurred speech, impaired coordination (ataxia), and in severe cases, coma. While this condition is rare in the general population, it is a well-documented complication in individuals with compromised gut anatomy or function.

Impact on calcium and magnesium levels 🔗

Excessive D(-) lactic acid in the body can have downstream effects on mineral balance. When lactic acid levels rise, the body’s buffering systems are activated, and this process can lead to the loss of calcium and magnesium through urine. Calcium is essential for bone health, muscle contraction, and nerve signalling, while magnesium plays a critical role in enzyme function, energy metabolism, and maintaining a normal heartbeat. Studies on critically ill patients have shown that low magnesium levels are independently associated with increased risk of lactic acidosis, suggesting a two-way relationship between mineral depletion and acid accumulation.

Prolonged or repeated episodes of mild D-lactic acid excess – even below the clinical threshold for acidosis – could gradually contribute to mineral depletion, particularly in individuals who already have marginal calcium or magnesium intake.

Other harmful effects of fermented foods 🔗

Mycotoxin contamination 🔗

Fermented foods, especially those involving fungal cultures (such as tempeh, miso, and certain cheeses), carry a risk of mycotoxin contamination. Mycotoxins are toxic secondary metabolites produced by moulds belonging to genera like Aspergillus, Fusarium, and Penicillium. Aflatoxins, ochratoxin A, and patulin are among the most concerning mycotoxins found in fermented products. Chronic exposure to aflatoxins is strongly linked to liver cancer. The risk is higher when contaminated raw materials are used or when fermentation conditions are poorly controlled.

Ethyl carbamate (urethane) 🔗

Ethyl carbamate is a process contaminant that can form during fermentation and storage of foods containing nitrogen-rich compounds like urea and citrulline. According to the U.S. FDA, low levels of ethyl carbamate are found in breads, soy sauce, beer, and wine. Higher concentrations occur in distilled spirits, particularly those made from stone fruits. Ethyl carbamate is classified as a probable human carcinogen, and its carcinogenic potential lies in its ability to form DNA adducts after metabolic activation, increasing the risk of cancers in the lungs, liver, and lymphatic system.

Microbial contamination and bacterial toxins 🔗

Spontaneous or poorly controlled fermentation – particularly in home and small-scale settings – can allow pathogenic bacteria to proliferate alongside the desired fermenting organisms. Cases of foodborne illness have been reported in association with fermented cheese, sausages, fish, and cereals. Endotoxins and enterotoxins produced by contaminating bacteria like Staphylococcus, Bacillus cereus, and Clostridium species can cause vomiting, diarrhoea, and more serious illness. Proper hygiene, quality raw materials, and the use of well-characterised starter cultures are the most effective safeguards.

How to reduce risks from fermented foods 🔗

The goal is not to avoid fermented foods entirely – their nutritional and probiotic benefits are well-established. Instead, it’s about making informed choices. Here are practical ways to minimise the risks:

Choose products with controlled fermentation: Commercially produced fermented foods made with defined starter cultures tend to have lower and more consistent levels of biogenic amines and other harmful byproducts compared to spontaneously fermented products.

Monitor storage conditions: Biogenic amine levels can continue to rise during storage, especially at higher temperatures. Proper refrigeration of fermented products is essential.

Be cautious with high-risk foods: Aged cheeses, fermented fish products, fermented sausages, and certain fermented soy products tend to have the highest biogenic amine levels. If you are sensitive to histamine or take MAOI medications, limit intake of these items.

Practice good hygiene in home fermentation: Use clean equipment, quality raw ingredients, and follow established recipes. Contamination from poor hygiene or inappropriate packaging is a leading cause of safety issues in traditionally fermented foods.

Introduce fermented foods gradually: If you are new to consuming fermented foods, start with small servings to assess your body’s response, particularly if you have any gastrointestinal conditions or food sensitivities.

The bigger picture 🔗

Fermentation has been a cornerstone of human food culture for thousands of years. It preserves food, enhances flavour, and produces health-promoting compounds. But like any biological process, it comes with trade-offs. The formation of biogenic amines, D(-) lactic acid, ethyl carbamate, and the potential for mycotoxin or bacterial contamination are real risks – especially when fermentation is uncontrolled, raw materials are substandard, or the consumer has particular health vulnerabilities.

Modern food science is addressing these challenges through better starter culture technology, improved quality control protocols, and ongoing research into mitigation strategies. For consumers, the key takeaway is simple: fermented foods can be a healthy part of your diet, but quality, source, and individual health context all matter.

What do you think? Have you ever experienced any adverse reactions after eating fermented foods like aged cheese or kimchi? And given the potential risks of uncontrolled fermentation, do you think stricter regulation of biogenic amine levels in fermented products – beyond just fish – is overdue?

References

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