My Healthcare News & Research — February 12, 2026

Fish Oil's Cancer Benefit May Hinge on a Single Enzyme

In mid-February 2026, a finding from Michigan Medicine and the University of Texas MD Anderson Cancer Center moved through the health-news cycle with an uncomfortable headline: your daily fish-oil capsule may not do what you think, and in one specific biological context it might even do the opposite. The underlying peer-reviewed study appeared online in Cellular and Molecular Gastroenterology and Hepatology in August 2025; the February 2026 press coverage from the University of Michigan is what carried it to a general audience. The core result is worth understanding precisely, because it is neither “fish oil is bad” nor “fish oil is good.” It is a story about a single enzyme.

Table of Contents

  1. 1. What the Study Found
  2. 2. EPA, DHA, and the ALOX15 Enzyme
  3. 3. The Numbers
  4. 4. What It Means
  5. 5. Honest Caveats
  6. 6. The Takeaway
  7. Sources

1. What the Study Found

Working in mice, the team led by Imad Shureiqi tested whether the two main omega-3 fatty acids in fish oil — EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) — protect against colorectal cancer. The answer depended entirely on whether the colon still carried a working copy of an enzyme called ALOX15, or 15-lipoxygenase-1. When ALOX15 was present, EPA in particular reduced both the number and the size of tumors. When ALOX15 was missing, the benefit vanished — and feeding the mice fish oil, especially DHA, was associated with more colorectal tumors, not fewer. In other words, the same supplement pointed in opposite directions depending on one host factor.

2. EPA, DHA, and the ALOX15 Enzyme

Omega-3s do not fight inflammation by themselves. The body has to convert EPA and DHA into a family of signaling molecules called resolvins, which actively switch off the inflammatory programs that can nudge healthy tissue toward cancer. ALOX15 is one of the enzymes that performs that conversion in the colon. The catch — and the reason this matters for people — is that ALOX15 is frequently switched off in the human colon as colorectal tumors develop. So the very tissue where you would most want omega-3s to work is often the tissue least equipped to activate them. Without the enzyme, EPA and DHA are not turned into the protective resolvins, and the raw fatty acids appear to feed a different, less favorable set of pathways.

3. The Numbers

Roughly 19 million adults in the United States take fish-oil supplements, which is what makes even a mouse study like this newsworthy. The researchers did not report a single clean percentage for humans — this was an animal experiment — but the direction of the effect was consistent across the models: EPA outperformed DHA, and the presence or absence of ALOX15 flipped the outcome from tumor-suppressing to tumor-promoting. That is a qualitative, mechanistic result, not a dosing table, and it should be read as one.

4. What It Means

The practical message the authors themselves emphasize is modest: not all fish-oil regimens are equal, and the benefit may be conditional on biology that varies from person to person. Shureiqi’s group is now developing drugs intended to restore or boost ALOX15 activity in colon cells, on the theory that pairing such a drug with omega-3s could rescue the protective pathway in people whose enzyme has been lost. That is a research direction, not an available treatment — but it reframes fish oil from a one-size-fits-all supplement into something closer to a conditional tool whose usefulness depends on the machinery already present in your tissue.

5. Honest Caveats

Several cautions belong in bold. First, this is a preclinical mouse study. Mouse colon-cancer models are useful for working out mechanism but map imperfectly onto human disease, and no one should conclude from this that fish oil causes cancer in people. Second, the finding does not dent the established safety record of omega-3s; large human trials have found fish oil to be well tolerated. Third — and this is the honest backdrop to almost every supplement headline — the biggest randomized trials of omega-3 have generally come back null. The landmark VITAL trial randomized nearly 25,900 U.S. adults to 1 gram of marine omega-3 daily or placebo and found no significant reduction in either total cancer (hazard ratio 1.03) or major cardiovascular events (hazard ratio 0.92) over about five years. The new enzyme work is valuable precisely because it offers a plausible reason why omega-3 results are so inconsistent: if the benefit depends on a host enzyme that some people have lost, then averaging everyone together would blur a real effect in one subgroup into an overall null. Finally, there is no commercial test to check your own ALOX15 status, so this research cannot yet guide any individual’s decision to take or skip fish oil.

6. The Takeaway

For now, the sensible reading is the one the researchers offer: talk to your doctor before starting fish oil, especially if you have a personal or family history of colorectal cancer, and never treat a supplement as a substitute for screening such as colonoscopy. Eating whole fish remains well supported for general health, and nothing here argues against it. What this study changes is not the grocery list but the mental model: omega-3s are not a uniform good delivered to a uniform body. Their effect runs through enzymes and pathways that differ from one person to the next — and the science of matching the right supplement to the right biology is only beginning.

Sources

  1. Michigan Medicine (University of Michigan) Health Lab. “Fish oil supplements may not work for certain cancer patients.” February 2026. michiganmedicine.org/health-lab
  2. ScienceDaily. “Omega-3 fish oil supplements could backfire without this key enzyme.” February 12, 2026. sciencedaily.com/releases/2026/02/260212234216
  3. Zuo X, Kiyasu Y, Liu Y, Deguchi Y, Liu F, Moussalli M, Tan L, Wei B, Wei D, Yang P, Shureiqi I. “Colorectal 15-Lipoxygenase-1 as a Host Factor Determining the Effects of Eicosapentaenoic Acid and Docosahexaenoic Acid on Colorectal Tumorigenesis in Mice.” Cellular and Molecular Gastroenterology and Hepatology. Published online August 14, 2025. doi:10.1016/j.jcmgh.2025.101607
  4. Manson JE, Cook NR, Lee IM, et al. “Marine n-3 Fatty Acids and Prevention of Cardiovascular Disease and Cancer” (VITAL trial). New England Journal of Medicine. 2019;380(1):23–32. PMID 30415637
  5. PubMed topic search: 15-lipoxygenase-1 EPA DHA colorectal resolvins

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