Mislabeled Fish Can Cause Oily Digestive Side Effects
The ingestion of certain fish species can cause involuntary discharge in some adults.
Updated on Oct. 29, 2026 in Nutrition
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A soccer player recently experienced keriorrhea, an involuntary oily rectal discharge, after consuming two servings of fish mislabeled as butterfish. This digestive condition occurs when the body cannot break down certain wax esters found in species like escolar, which are sometimes sold under different names.
Why it matters
Understanding that fish sold as white tuna, cod, or butterfish may actually be escolar helps diners identify potential sources of unexpected digestive distress. Because escolar is often mislabeled, consumers concerned about food sensitivities should be aware that these wax esters pass through the system unchanged.
A 2009 study found that 5 of 9 samples sold as white tuna in New York City and Denver were actually escolar. It remains unknown how often similar mislabeling occurs in current global restaurant markets.
The players
Health Canada
A federal government agency responsible for food safety and health policy that currently permits the sale of escolar.
The details
Escolar and oilfish contain high concentrations of gempylotoxin, a type of indigestible wax ester that can account for up to 20 percent of the fish's body weight. When consumed, these wax esters are not absorbed by the human digestive tract. Consequently, they pass through the intestines and are excreted as an oily, involuntary discharge known as keriorrhea.
Timeline
2002: 98 people reported illness after eating fish in Australia.
2009: A study identified mislabeled white tuna samples in New York City and Denver.
2020: The soccer player case report was published in BMJ Case Reports.
Health Landscape
This case highlights the variation in international food safety standards, as countries like Italy, Japan, and South Korea have banned the sale of escolar due to its digestive effects. These regulations contrast with jurisdictions like Canada where the fish remains legal for sale.
Consumers should be aware that fish marketed as butterfish, cod, or white tuna may sometimes be mislabeled escolar. If you experience unexpected oily stools after eating seafood, the symptoms typically resolve within hours, though you may discuss any persistent concerns with your doctor.
The takeaway
Keriorrhea is a transient, non-painful condition resulting from the body's inability to digest specific wax esters found in certain fish. If you suspect an adverse reaction to a seafood meal, observe your symptoms over several hours and consult a physician if you experience discomfort.
Further reading
For more information on food safety and dietary health, visit our Nutrition section.
Source note: This article includes information reported by Medical Daily.
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