In the United States, roughly 19 million adults reach for fish‑oil capsules, attracted by the promise of omega‑3 fatty acids—EPA and DHA—to curb inflammation and lower chronic‑disease risk.
When it comes to cancer, the picture is far from clear. While a handful of large trials hinted that omega‑3s might protect against malignancies, other studies reported no benefit—or even a slight rise in cancer cases.
A Gene That May Decide Omega‑3 Success in the Colon
Scientists from the University of Michigan and MD Anderson Cancer Center dug deeper into this puzzle. Their work, published in Cellular and Molecular Gastroenterology and Hepatology, identified the enzyme 15‑lipoxygenase‑1 (ALOX15) as a pivotal player. Without enough ALOX15, EPA and DHA struggle to convert into anti‑inflammatory molecules that could suppress colorectal tumors.
Unexpected Findings From Mouse Experiments
To test the theory, researchers fed two groups of mice either a standard diet or one enriched with fish oil. Surprisingly, the fish‑oil‑fed mice developed more colon tumors after being exposed to chemicals that provoke inflammation.
Normally, EPA and DHA are transformed into resolvins—compounds that help calm chronic inflammation. This conversion relies on ALOX15, which is frequently turned off in many cancers.
When the team studied mice genetically engineered to lack ALOX15, they observed a surge in tumor numbers, although the effect varied between EPA and DHA.
EPA Beats DHA in Tumor Prevention, But Form Matters
Animals consuming EPA‑rich diets produced fewer tumors than those receiving DHA. Both fatty acids come in several chemical forms: free fatty acids, ethyl esters, and triglycerides.
Lovaza, an FDA‑approved prescription containing ethyl‑ester EPA and DHA, is used to lower high triglyceride levels. In the study, Lovaza and other EPA ethyl‑ester or free‑fatty‑acid versions cut both tumor count and size—especially in mice with active ALOX15. DHA‑based preparations, however, failed to curb tumor growth when ALOX15 was missing, though they showed some benefit when the enzyme was present.
"Not all fish‑oil products are created equal," explains Dr. Imad Shureiqi, a professor of internal medicine at the University of Michigan. "We also need to know whether a person’s body can actually process these fats into anti‑inflammatory agents before expecting any cancer‑preventive effect."
What This Means for People Considering Fish Oil
Although the bulk of evidence comes from animal models, the findings raise a cautionary flag. Individuals with colon polyps—or anyone worried about colorectal cancer—who lack functional ALOX15 may not reap the hoped‑for protective benefits from EPA or DHA supplements.
Dr. Shureiqi advises discussing any new supplement regimen with a healthcare professional, especially if you have a personal or family history of colon cancer.
The research team is now exploring drugs that could boost ALOX15 activity inside cancer cells, aiming to restore the body’s capacity to turn omega‑3s into tumor‑fighting compounds.