The Core Reason: High Erucic Acid Content
The primary reason that pressed mustard oil is illegal for cooking in the United States revolves around its high concentration of erucic acid. Erucic acid is a monounsaturated omega-9 fatty acid that is prevalent in plants of the Brassicaceae family, which includes mustard. In traditional mustard oil, the erucic acid content can be as high as 40-50%. It is this elevated level that triggered regulatory action by the FDA decades ago.
The Historical Animal Studies
The FDA's ban is largely based on animal studies, particularly those conducted on rats in the 1970s. These studies suggested that consuming diets high in erucic acid could lead to a heart condition called myocardial lipidosis, which is the accumulation of fatty deposits in the heart muscle. While these animal studies showed adverse effects, the application of these findings directly to humans remains a point of controversy. Critics point out that animal metabolisms differ significantly from humans, and the test animals were fed extremely high doses of erucic acid.
The FDA's Regulatory Stance
FDA Prohibition and Labeling
The FDA's stance is based on the precautionary principle, which prioritizes public safety by preventing potential harm, even if definitive human evidence is lacking. The agency strictly prohibits the sale of expressed (pressed) mustard oil for human consumption. This is why bottles of mustard oil in American grocery stores, often found in the ethnic foods aisle, must be explicitly labeled "For External Use Only". The FDA uses an import alert to detain expressed mustard oil shipments intended for culinary use.
Distinguishing Expressed vs. Essential Mustard Oil
It is important to understand that not all products derived from mustard seeds are banned from the food supply. There are two main types of mustard oil, which are regulated differently by the FDA.
- Pressed or Expressed Mustard Oil: This is the high-erucic acid oil extracted directly from mustard seeds. It has the pungent, sharp flavor that is characteristic of mustard and is the type banned for cooking.
- Essential Mustard Oil: This volatile oil is produced by distilling mustard seed and mixing the ground seeds with water. It has a much lower erucic acid content and is classified by the FDA as "Generally Recognized As Safe" (GRAS) for use as a flavoring agent in small quantities.
The Controversy: Differing Views on Safety
Despite the US ban, mustard oil is one of the most widely consumed cooking oils in the Indian subcontinent, and it has been for centuries. Many South Asian health organizations, like the Lipid Association of India, have even endorsed it as a heart-healthy oil. This stark contrast highlights the ongoing debate about erucic acid's effect on human health.
Conflicting Human and Animal Data
| Feature | Conventional Mustard Oil (Banned) | Canola Oil (FDA Approved) |
|---|---|---|
| Erucic Acid Content | Very High (up to 50%) | Very Low (less than 2%) |
| Development History | Traditional, unrefined oil used for centuries | Modern cultivar developed in Canada to be low-acid |
| FDA Status | Not permitted for cooking; labeled "For External Use Only" | Generally Recognized As Safe (GRAS) for human consumption |
| Primary Basis for FDA Action | Decades-old rat studies showing heart health issues | Explicitly bred to be a safe, low-erucic acid food product |
The Canola Connection
In response to initial health concerns over high-erucic acid oils, Canadian researchers developed a new variety of rapeseed in the 1950s that was specifically bred to have low levels of erucic acid. This oil was trademarked as "Canola," a portmanteau of "Canadian oil, low acid". This low-erucic acid oil is considered safe and has become a staple cooking oil worldwide, but it is distinct from the traditional mustard oil that remains restricted.
Conclusion: A Precautionary Ban with Cultural Implications
The FDA's ban on pressed mustard oil for cooking in the US is a reflection of its stringent food safety standards, rooted in historical animal studies that raised concerns about erucic acid. While many in South Asia have used it safely for generations, the lack of definitive human research and the existence of safer alternatives like canola oil have cemented the FDA's precautionary stance. For consumers in the US, the "For External Use Only" label is not merely a suggestion but a legal requirement stemming from federal regulation. For those seeking mustard flavor, essential mustard oil is available as a flavoring agent, but the traditional oil remains a product for external use only. Learn more about the FDA's import alerts here.
Other Potential Health Considerations
In addition to erucic acid, other aspects of mustard oil use are worth noting:
- Risk of adulteration: Historically, mustard oil has been known to be adulterated with argemone oil, which is toxic and can cause epidemic dropsy.
- Allergic reactions: The topical application of mustard oil can cause skin irritation or allergic reactions in sensitive individuals.
- Digestive issues: Consuming large quantities of mustard oil can lead to digestive discomfort like stomach upset or diarrhea.
- Respiratory effects: When heated, the pungent fumes from mustard oil can cause respiratory irritation for some people, especially those with asthma.
