Scientists discovered why fish oil supplements work differently for different people when it comes to preventing colon cancer. The key is an enzyme called ALOX15 that’s often missing in people at risk for colon cancer. When researchers gave mice this enzyme and fed them fish oil supplements (EPA and DHA), the supplements successfully stopped tumor growth. Without the enzyme, the same fish oil didn’t help much. This finding explains why previous studies on fish oil and cancer prevention have given mixed results—it all depends on whether your body has this important enzyme working properly.

The Quick Take

  • What they studied: Whether fish oil supplements (EPA and DHA) can prevent colon cancer, and what determines if they actually work
  • Who participated: Multiple groups of laboratory mice engineered to develop colon cancer, some with a special human enzyme added to their gut cells and some without
  • Key finding: Fish oil supplements only stopped tumor growth in mice that had the ALOX15 enzyme in their colon cells. In mice without this enzyme, the same supplements had little to no effect on cancer prevention.
  • What it means for you: If you’re considering fish oil supplements for cancer prevention, your body’s ability to process these supplements depends on whether you have adequate levels of a specific enzyme. This may explain why fish oil works great for some people but not others. Talk to your doctor about whether testing for this enzyme might be helpful for you.

The Research Details

Researchers used specially bred laboratory mice that naturally develop colon cancer, similar to how humans get the disease. They created some mice with an added human gene that produces the ALOX15 enzyme in their intestinal cells, while other mice didn’t have this gene. Both groups were then fed fish oil supplements in different forms. The scientists measured how much tumor growth occurred in each group and analyzed what was happening at the cellular level—looking at special healing molecules called resolvins, immune cells, and inflammatory chemicals.

They also did lab experiments with mouse immune cells to understand exactly how the resolvins (products made from fish oil when ALOX15 is present) affect cancer-fighting processes. This combination of whole-animal studies and detailed cellular experiments allowed them to understand both whether fish oil worked and why it worked.

This research design is important because it shows that the same supplement can have completely different effects depending on a single biological factor. Previous studies on fish oil and cancer gave conflicting results because researchers didn’t know about this enzyme requirement. By identifying ALOX15 as the critical factor, this work explains the confusion and points toward better ways to predict who will benefit from fish oil supplements.

This study used multiple mouse models that closely mimic human colon cancer development, which is a strength. The researchers measured outcomes at multiple levels—from tumor size down to individual molecules—providing comprehensive evidence. However, this is animal research, so results may not translate exactly to humans. The study was published in a peer-reviewed scientific journal, indicating it passed expert review. The lack of human participants means we need follow-up studies in people before making definitive recommendations.

What the Results Show

The most striking finding was that fish oil supplements (EPA and DHA) behaved completely differently depending on whether mice had the ALOX15 enzyme. In mice without the enzyme, fish oil supplements produced minimal amounts of healing molecules called resolvins and had unpredictable effects on tumor growth—sometimes helping a little, sometimes not at all.

In contrast, mice engineered to produce ALOX15 in their intestinal cells showed consistent, strong benefits from fish oil supplements. These mice developed significantly fewer and smaller tumors. The fish oil supplements were converted into resolvins much more efficiently, and these resolvins triggered a cascade of protective effects: they reduced inflammatory chemicals in the colon (CCL2, IL-1β, and IL-6), decreased harmful immune cells called tumor-associated macrophages, and increased beneficial immune cells (CD8+ T cells) that fight cancer.

When researchers tested the specific resolvins in laboratory dishes with immune cells, they confirmed that these molecules directly suppressed the production of inflammatory chemicals and boosted the cancer-fighting ability of immune cells. This provided a clear mechanism explaining how fish oil prevents cancer—but only when ALOX15 is present to convert it into resolvins.

The research revealed that ALOX15 acts as a critical gatekeeper. Without it, fish oil supplements accumulate in the body but don’t get converted into the protective resolvins. The inflammatory environment in the colon remains unchanged, and tumors develop at normal rates. The study also showed that different formulations of EPA and DHA supplements all required ALOX15 to be effective, suggesting the enzyme is universally necessary rather than just helpful for certain types of supplements.

Previous research on fish oil and colon cancer has produced conflicting results—some studies showed benefits, others showed no effect, and a few even suggested potential harm. This research explains why: studies didn’t account for ALOX15 status in their participants. People with adequate ALOX15 expression would show benefits from fish oil, while those with low or absent ALOX15 would see no benefit. This finding reconciles the contradictory literature and suggests that future studies should measure ALOX15 levels to properly evaluate fish oil’s effectiveness.

This research was conducted entirely in mice, not humans. While the mouse models closely resemble human colon cancer development, results don’t always translate directly to people. The study didn’t measure ALOX15 levels in human colon tissue or test whether the findings apply to people with different genetic backgrounds. Additionally, the research used laboratory conditions that may not reflect real-world factors like diet, stress, and other lifestyle elements that affect cancer risk. Finally, the study doesn’t tell us how common low ALOX15 levels are in the general population or how to safely test for this enzyme in living people.

The Bottom Line

Based on this research, fish oil supplements may help prevent colon cancer, but only if your body can properly process them through the ALOX15 enzyme. Current evidence suggests: (1) If you have a family history of colon cancer or other risk factors, discuss fish oil supplementation with your doctor—it may be beneficial if you have adequate ALOX15 function. (2) Don’t rely on fish oil supplements alone for cancer prevention; maintain other protective habits like eating fiber-rich foods, exercising, and getting screening colonoscopies as recommended. (3) Ask your doctor whether testing for ALOX15 status might be appropriate for you, though this test isn’t yet widely available. Confidence level: Moderate for the basic finding (enzyme requirement is clear), but low for human recommendations (more research needed).

This research is most relevant for people with a family history of colon cancer, those with inflammatory bowel disease, and anyone considering fish oil supplements specifically for cancer prevention. It’s also important for healthcare providers developing personalized cancer prevention strategies. People without colon cancer risk factors may still benefit from fish oil for other health reasons (like heart health), but this research doesn’t address those uses. Anyone currently taking fish oil supplements should continue them unless their doctor advises otherwise—this research doesn’t suggest they’re harmful, just that effectiveness depends on individual biology.

In the mouse studies, tumor prevention effects appeared over several months of supplementation. In humans, cancer prevention is a long-term process—it typically takes years or decades for colon cancer to develop, so benefits from supplements would likely take months to years to become apparent. Don’t expect immediate results; cancer prevention is about reducing risk over time, not providing quick fixes.

Want to Apply This Research?

  • If you’re taking fish oil supplements, track: (1) Daily supplement intake (type, dose, and brand), (2) Digestive symptoms (bloating, changes in bowel habits), (3) Energy levels and overall wellness, and (4) Any new health concerns. This creates a personal record to discuss with your doctor about whether the supplements seem beneficial for you specifically.
  • Start by discussing fish oil supplementation with your healthcare provider, especially if you have colon cancer risk factors. If your doctor recommends fish oil, use the app to: (1) Set a daily reminder to take your supplement consistently, (2) Log which type of fish oil you’re taking (EPA/DHA amounts matter), (3) Note any changes in how you feel, and (4) Schedule regular check-ins with your doctor to assess whether supplementation is right for you.
  • Over 3-6 months, track consistency of supplement use and any health changes. Every 6-12 months, review your notes with your doctor to determine if fish oil supplementation is working for your individual situation. If you develop new symptoms or your risk factors change, update your doctor. Consider whether you’re also maintaining other cancer-prevention habits (screening, diet, exercise) alongside supplementation.

This research summary is for educational purposes only and should not be considered medical advice. Fish oil supplements are not proven cancer treatments or guaranteed preventatives. The findings are based on animal research and have not yet been confirmed in humans. Before starting, stopping, or changing any supplement regimen, especially if you have a personal or family history of cancer, inflammatory bowel disease, or are taking blood-thinning medications, consult with your healthcare provider. Fish oil supplements can interact with certain medications and may increase bleeding risk in some individuals. This summary does not replace professional medical evaluation or personalized medical recommendations.