You might already include fatty fish in your nutrition to boost your omega-3 fatty acids since they're good for your heart, brain, cholesterol and mental health. But did you know that healthy fats may also protect you from cancer?

A recent study analyzed data from more than 250,000 participants (from the UK) over a decade and found that higher levels of omega-3 and omega-6 fatty acids were associated with a lower risk of developing various types of cancer.

More specifically, higher levels of omega-3 were linked to lower rates of colon, stomach, hepatobiliary and lung cancer. Higher levels of omega-6 were connected to lower rates of 14 different cancers, including brain, skin, esophageal, lung, bladder and colorectal cancer.

This doesn't necessarily mean that taking fish oil is a get-out-of-cancer-free card. While polyunsaturated fatty acids are often used in patients with cancer to help improve outcomes, we want to point out that correlation does not equal causation. But this study certainly offers yet another compelling reason to make sure you're getting enough healthy fats in your diet!

Fatty acids and cancer: What the study found

The analysis was done on participants in the UK Biobank study, a large-scale observational study. Interestingly, the benefits of a higher intake of polyunsaturated fatty acids (PUFAs) were not dependent on factors like BMI, physical activity or alcohol use. In other words, individuals who were overweight or inactive who consumed greater amounts of PUFAs still were less likely to be diagnosed with cancer than those with a lower intake.

These findings point to the importance of including an adequate intake of healthy fats in our daily diets. The study also highlights the importance of balanced omega-6 and omega-3 levels, meaning how much of each you're getting. Consuming a disproportionate amount of omega-6—too high of a ratio—is associated with an increased risk of cancer overall. We'll talk about this more in a minute!

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Can fatty acids benefit cancer patients?

Polyunsaturated fatty acids probably can! While more research is needed, yes, PUFAs may be beneficial for cancer patients.

Yet another finding noted in the study was that a previous meta-analysis of other research found that omega-3 consumption—specifically, the intake of fish or marine omega-3 polyunsaturated fatty acids—was linked to lower mortality in cancer patients.

So, fatty acids can be beneficial to help prevent a cancer diagnosis and for patients with cancer.

How do omega-3 and omega-6 fatty acids impact different types of cancer?

Polyunsaturated fatty acids' specific effects on different types of cancer are still unclear. However, as we noted above, they show varying effects in observational studies.

In the above study, omega-3 consumption was associated with a lower risk of colon, stomach and lung cancer. Omega-6 consumption was associated with lower rates of brain and skin cancer, among 12 others.

The study did find one exception: prostate cancer, which had a positive correlation with a higher omega-3 consumption. Put differently, higher levels of omega-3 were related to a higher incidence of prostate cancer.

Also worth noting is that certain cancers, including ovary, uterus, and breast cancer, weren't associated with fatty acids at all. (At first, the researchers did notice a relationship between uterus, ovary, and breast cancer and omega-6 fatty acids. However, after they controlled other variables, such as oral contraceptive use, the relationship disappeared.)

Important note: None of this means that eating polyunsaturated fatty acids causes or prevents cancer. What we have are observed relationships. Furthermore, science has not yet determined exactly why PUFAs may help prevent cancer. One theory noted in the study suggests polyunsaturated fatty acids serve as precursors to lipid mediators, molecules that may help regulate metabolic pathways and the inflammatory response.

Plus, as we've already known for years, a healthy diet significantly helps lower the risk of cancer, and healthy fatty acids (like fish oil) are a critical part of a well-rounded nutrition plan. Increasing healthy fatty acid plasma levels and maintaining an optimal ratio of omega-6 to omega-3 are both associated with better health outcomes.

What are the best dietary sources of omega-3 and omega-6 fatty acids?

The most beneficial sources of omega-3 fatty acids include:

1. Oily fish like salmon, herring, sardines and tuna
2. Flaxseed (including its oil)
3. Walnuts
4. Chia seeds

For more omega-6, look to:

1. Safflower oil
2. Sunflower seeds and oil
3. Soybeans (tofu, oil, etc.)
4. Walnuts (yep, this superfood contains both types of the "good" omega!)
5. Pumpkin seeds
6. Peanuts
7. Egg yolks
8. Cashews

What is the difference between omega-3 and omega-6?

Omega-3 and omega-6 are often confused, and we're going to make things trickier: There are actually four major types of dietary fats or lipids. Fatty acids are the building blocks of dietary fats and have long carbon chains that have all single bonds or one or more two (double) bonds. The types of bonds affect the structure (or shape) of the chain.

1. Polyunsaturated fats

Also known as PUFAs, they're considered the healthiest type of fat and are found in seeds, nuts, oils and fatty fish in abundance. They have more than one (poly) double bond and are not saturated, so the chain is very bent. Under the umbrella of polyunsaturated fats, there are other types, including omega-3 and omega-6 fatty acids, and even more types! For instance, two types of omega-3s are docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Linoleic acid is an example of an omega-6 fatty acid.

What's the difference between omega-3 and omega-6 fatty acids? It's the location of the first double bond. In omega-3, the first double bond occurs on the third carbon atom. In omega-6, it occurs on the sixth carbon atom. The double bond location changes the shape of the chain that makes these fatty acids, and that's why they have a different impact on the body (although both play an important role in your overall health).

2. Saturated fats

These lipids all have "saturated" carbon bonds, meaning only single bonds—they look like straight chains. Typically, saturated fats are solid at room temperature and come (mostly) from animal sources, like butter and animal fat. (Think of how butter turns to liquid when heated.) Like many things in life, too much saturated fat can be a bad thing. In this case, it can increase your risk of cardiovascular concerns. This is why your healthcare provider might recommend that you limit your intake of highly processed, refined and packaged foods.

3. Monounsaturated fats

Also known as MUFAs, these lipids have only one (mono) double bond in their chain. Unlike saturated fats, the chain is slightly bent. Typically, they're liquid at room temperature but solidify when they cool. Avocado, canola, safflower, sesame, and olive oils are all great ways to consume monounsaturated fats in moderation.

4. Trans-fats

These are the ones you want to avoid. Dietary trans-fat generally is not naturally occurring, like saturated fats are. It's the result of industrial processes that add hydrogen to liquid vegetable oils, creating a double bond that causes the hydrogens to face opposite directions. Watch out for "partially hydrogenated oil" on your food labels. Limit trans-fat in your diet as much as possible.

How can I test my omega fatty acid levels?

Reevaluating your diet can give you an idea of how much of each type of fatty acid you're consuming. However, the only accurate way to determine your levels is with a lab test.

Make sure you're not only getting enough of each fatty acid, but that the ratio between the two is in the ideal range. If you're consuming too much omega-6 compared to omega-3, it can have an adverse effect on your health. We recommend a ratio of <4:1.

To rectify this, you can try consuming more omega-3 fatty acids via fish or supplementation, rather than cutting back on your consumption of omega-6. Consult with your healthcare provider before making dietary, supplementation or other lifestyle changes.

Healthy fats are your friend

Low-fat diets are out. Your body needs you to consume enough healthy fats—countless studies show this! Even if you're vegan, you can improve your intake of omega-3 and omega-6 in your nutrition and boost your cancer prevention.

In the right amounts, and from safe and healthy sources, fats are going to be one of your very best friends.

 

References

• Fabian CJ, Kimler BF. "Marine-Derived Omega-3 Fatty Acids: Fishing for Clues for Cancer Prevention." American Society of Clinical Oncology Educational Book. May 2013. https://ascopubs.org/doi/10.14694/EdBook_AM.2013.33.97
• Freitas RDS, Campos MM. "Protective Effects of Omega-3 Fatty Acids in Cancer-Related Complications." Nutrients. April 2019. https://pmc.ncbi.nlm.nih.gov/articles/PMC6566772/
• Zhang Y, et al. "Associations of plasma omega-6 and omega-3 fatty acids with overall and 19 site-specific cancers: A population-based cohort study in UK Biobank." International Journal of Cancer. October 2024. https://onlinelibrary.wiley.com/doi/10.1002/ijc.35226
• "High levels of omega-3, omega-6 may protect against cancer." ScienceDaily. November 2024. https://www.sciencedaily.com/releases/2024/11/241104112234.htm
• "Monounsaturated Fats." American Heart Association. October 2023. https://www.heart.org/en/healthy-living/healthy-eating/eat-smart/fats/monounsaturated-fats
• "No need to avoid healthy omega-6 fats." Harvard Health Publishing. August 2019. https://www.health.harvard.edu/newsletter_article/no-need-to-avoid-healthy-omega-6-fats
• "Polyunsaturated Fats." American Heart Association. October 2023. https://www.heart.org/en/healthy-living/healthy-eating/eat-smart/fats/polyunsaturated-fats
• "Saturated Fat." American Heart Association. August 2024. https://www.heart.org/en/healthy-living/healthy-eating/eat-smart/fats/saturated-fats
• "Trans Fat, Saturated & Unsaturated Fats, Healthy & Unhealthy Fats." PMF IAS. April 2021. https://www.pmfias.com/fats-saturated-unsaturated-trans-fat/
• "Trans Fats." American Heart Association. March 2017. https://www.heart.org/en/healthy-living/healthy-eating/eat-smart/fats/trans-fat

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