Understanding Indigestible Wax Esters
Indigestible wax esters are a type of oily substance that some marine life, particularly certain deep-sea fish, use for buoyancy. Unlike the fat (triglycerides) found in most fish, which humans can easily digest, these wax esters are poorly absorbed by the human digestive system. When consumed in large quantities, these compounds can accumulate in the rectum, leading to a condition known as keriorrhea, characterized by an oily, orange or yellow leakage. While the symptoms are generally not life-threatening, they can be highly unpleasant and embarrassing, including stomach cramps, nausea, and vomiting.
The main culprits: Escolar and Oilfish
The primary sources of concern for consumers are fish from the Gempylidae family, which includes escolar and oilfish. These predatory fish are found worldwide in tropical and temperate waters.
- Escolar (Lepidocybium flavobrunneum): Also known as snake mackerel or sometimes mislabeled as 'white tuna', this fish can contain up to 20% indigestible oil by weight. Its rich, buttery flavor comes from this oil, but its consumption is linked to adverse gastrointestinal effects in a significant portion of the population.
- Oilfish (Ruvettus pretiosus): This species is a close relative of escolar and is also known to cause similar gastrointestinal distress due to its high wax ester content. In fact, it is sometimes referred to as 'castor oil fish'.
The issue of mislabeling
A major problem contributing to keriorrhea outbreaks is the mislabeling of escolar and oilfish. Due to their rich flavor, they are often sold under more marketable, yet misleading, names. This practice can trick unaware consumers into eating a larger portion than their bodies can handle. Common names used to mislabel these fish include:
- White Tuna
- Super White Tuna
- Hawaiian Butter Fish
- Sea Bass
- Rudderfish
- Codfish
This misidentification makes it difficult for consumers to make informed decisions. Several countries, including Japan and Italy, have banned the sale of escolar and oilfish entirely. The Food and Drug Administration (FDA) advises against marketing these species in the US.
The nuance: Some wax esters are digestible
It's important to distinguish the indigestible wax esters in some fish from other, non-harmful sources. For instance, the liquid wax ester jojoba oil, derived from the jojoba shrub, is used externally in cosmetics and does not cause digestive issues. Furthermore, a marine oil from the copepod Calanus finmarchicus contains wax esters that are considered bioavailable and may even offer health benefits, though they are digested more slowly than standard triglycerides. Human consumption of wax esters in moderate amounts is possible, depending on the source. The key is the high concentration and chemical makeup of the specific wax esters found in escolar and oilfish.
Comparison of Seafood and Their Wax Ester Content
This table highlights the difference in wax ester content and risk between different types of seafood.
| Feature | Escolar / Oilfish | Salmon | Tuna | Orange Roughy | Copepod Oil |
|---|---|---|---|---|---|
| Wax Ester Content | High (Up to 20% by weight) | Low to none (Primarily triglycerides) | Low to none (Primarily triglycerides) | Moderate (Up to 5.5% by weight) | High (Bioavailable form) |
| Digestion by Humans | Indigestible | Fully digestible | Fully digestible | Poorly digested | Slowly digested, with bioavailability |
| Gastrointestinal Risk | Keriorrhea, cramps, nausea | None | None | Potential for keriorrhea | None (at recommended doses) |
| Labeling Issues | Frequently mislabeled as 'white tuna', 'butterfish' | Generally correctly labeled | Generally correctly labeled | Sometimes mislabeled | Sold as specific nutraceutical |
| Preparation Tips | Limit portion size, grill to reduce oil, discard liquid | Standard cooking methods | Standard cooking methods | Limit portion size | Taken as a supplement |
How to safely eat fish with high wax ester content
For those who enjoy the taste of high-wax-ester fish and tolerate it well, there are ways to minimize the risk of digestive issues. Health authorities in various regions, including Queensland, Australia, recommend limiting intake and adjusting preparation methods.
- Eat small portions: Limiting your serving size to less than 200 grams can significantly reduce the chances of a reaction.
- Grill or broil: Cooking methods that allow the oily substance to drain away, such as grilling, can help decrease the amount of wax ester consumed. Be sure to discard any cooking liquids.
- Check for correct labeling: Always purchase fish from reputable sources and confirm the species, especially if purchasing something labeled with a generic or unusual name. Look for the scientific name to be sure.
- Consider your sensitivity: Individuals with pre-existing bowel conditions, children, and pregnant women should exercise extra caution or avoid these fish entirely.
Conclusion
While the rich, buttery flavor of fish like escolar and oilfish can be appealing, their high content of indigestible wax esters presents a significant gastrointestinal risk for many people. The resulting condition, keriorrhea, while not life-threatening, is highly undesirable. Consumers should be particularly vigilant about fish mislabeling, which often conceals the true identity of these species. By learning to identify these fish, controlling portion sizes, and using specific cooking techniques, individuals can minimize the risk. For those with sensitivities, opting for other popular fish species like salmon or cod is a safer choice. Being an informed consumer is the best defense against unknowingly consuming foods that cause an adverse reaction.
For more information on general seafood safety, consider resources such as the U.S. Food and Drug Administration's fish advice page.
