Only the Right Omega-3s Can Fight Cancer

Not all essential fatty acids are created equal; some actually promote cancer growth

Salmon and Omega-3In today’s weight-conscious, ever-expanding waistline world, many people have jumped on the fat-free bandwagon. While more and more research shows that fat is not the fearsome monster it has been portrayed as, calorie counter after calorie counter continues to eschew avocados and olive oil for fat-free (and nutrient-free) alternatives.

In our quest for a lower number on the scale, we may be unwittingly putting ourselves at risk for cancer. Yes, cancer.

According to a review of omega-3 studies, when the right type and form of these essential fatty acids (EFAs) are consumed, you can prevent as well as treat a number of cancers.[1]

Or, to say it another way, certain fats are actually cancer-protective.

The Many Faces of Omega-3s

When most people think of omega-3s, they immediately think of fish oil. And while it follows that all fish oil contains some omega-3s, not all omega-3s are fish oil.

Fish oil contains the long-chain omega-3s DHA and EPA. There are found primarily in deep, cold-water fish like salmon, tuna and mackerel.

While most people think that these fish themselves contain essential fatty acids, that’s not necessarily true. The fish take in EPA and DHA from the plankton they eat. In that sense, omega-3s are essential for fish as well.

Given this, not all fish are created equal. Fish from the warmer waters of the Atlantic likely contain less omega-3s than their Pacific cousins. And farm-raised fish fed grain-based pellets likely have very little EPA and DHA, well, naturally occurring anyway.

There is also a plant-based, short-chain omega-3 fatty acid: alpha linolenic acid (ALA). This is found in a variety of nuts, seeds, legumes and vegetables, including:

  • Walnuts
  • Flaxseed
  • Rapeseed (canola)
  • Soybeans
  • Olives
  • Kale
  • Spinach
  • Broccoli
  • Brussels sprouts

Of these, many of the seeds and nuts also contain the omega-6 fatty acid linoleic acid.

Now, here’s where it gets tricky. When you eat any of these essential fatty acids, your body converts them into other substances. For example, linoleic acid is converted into arachidonic acid, which can be inflammatory.

Similarly, alpha linolenic acid can be converted into EPA, while EPA can convert into DHA. However, less than 10 percent of ALA actually undergoes this conversion, and the EPA to DHA conversion is inefficient at best. Therefore, it is critical to eat foods that are naturally rich in EPA and DHA rather than counting on unreliable conversions.

This means cold-water fish from deep waters. And wild-caught, not farm-raised.

So, now that we know what, let’s take a look at why.

Balance is Key

Several studies have shown that omega-3 and omega-6 fatty acids have a Dr. Jekyll/Mr. Hyde thing going on when it comes to cancer. Omega-3s seem to be cancer-protective, while omega-6s tend toward promoting cancer.

This may be the key to why there is some discrepancy between studies looking at the benefits of omega-3s on cancer. Turns out, it’s all about the balance of omega-3s and omega-6s in the body.

Today’s standard American diet often contains more inflammatory omega-6s than anti-inflammatory omega-3s. But, when this ratio of omega-6s to omega-3s is lower than 5 to 1 (5:1 or less), research has found that cancer progression actually slows rather than progresses.[2] Any greater ratio and the omega-3s cannot override the dangers of the omega-6s.

But that’s not where the yin and yang stops. Omega-6s have been shown to promote tumor progression by activating cell growth,[3] while omega-3s alter this signal and reduce cell growth.[4]

To this point, a study found that mice given omega-3s had reduced growth of prostate tumors, while mice given omega-6s had the opposite effect.[5]

Based on this, researchers hypothesize that maintaining a diet rich in omega-3s and lower in omega-6s allows you to enjoy the cancer-protective benefits of essential fatty acids, while reducing your risk for the disease.

Omega-3s and Cancer

Now that we know the best type and form of omega-3s (deep, cold-water fish and EPA/DHA), and we understand that omega-6s can undermine omega-3s’ benefits, let’s look at how omega-3s really perform when it comes to cancer.

To do this, we have to turn to animal studies. The reason is it is easy to control a lab animal’s diet for weeks and months at a time, while humans tend to eat foods that could cloud the research.

What we’ve seen in mice studies is that supplementing the diet with omega-3-rich foods have helped to reduce prostate tumor growth,[6] reduce breast cancer tumors by 60 percent,[7] enhance the effectiveness of breast cancer drugs like tamoxifen,[8] suppress tumor growth,[9] and inhibit metastases of colon cancer.[10] In all cases, research was done using EPA and/or DHA.

Studies also show that omega-3 supplements (as opposed to eating omega-3-rich food) can also help treat and even protect against cancer. They have been shown to protect against colorectal cancer,[11] prostate cancer[12] and even skin cancer.[13]

Given all this, researchers conclude, “Experiments in animal models and tissue culture overwhelmingly support a protective effect of [omega-3 polyunsaturated fatty acids] against colon, prostate, and breast cancer.”[14]

They go on to suggest that human trials are inconsistent due to diet and environmental factors that are difficult to control.

Finally, they state, “Restoring a healthier balance of [omega-3 to omega-6 polyunsaturated fatty acids] is an attractive approach for cancer chemoprevention.”

This is No Fish Tale

So, to make sure we are on track, let’s quickly review the key findings regarding essential fatty acids and cancer:

1. Omega-3s are the ticket.

2. Aim for EPA and DHA from wild-caught, deep, cold-water fish like salmon, mackerel and tuna.

3. Keep your omega-3 to omega-6 ratio in balance, aiming for more 3s than 6s.

4. Omega-3 supplements work as well as food, provided you choose the right fish oil supplement.

In conclusion, to reap the cancer-protective benefits, you may want to eat fresh fish at least twice a week. And when it comes to omega-3 supplements, choose a product that contains oil from cold-water fish. Make sure it is mercury-free and toxin-free. Finally, it should contain at least 800 mg of actual omega-3s, with at least 250 mg of DHA and 400 mg of EPA.


[1] Berquin, IM et al. Multi-targeted therapy of cancer by omega-3 fatty acids. Cancer Lett. 2008 Oct 8;269(2):363-77.

[2] Berquin, IM et al. Modulation of prostate cancer genetic risk by omega-3 and omega-6 fatty acids. J Clin Invest. 2007;117:1,866–75.

[3] McCarty, MF. Fish oil may impede tumour angiogenesis and invasiveness by downregulating protein kinase C and modulating eicosanoid production. Med Hypotheses. 1996;46:107–15.

[4] Schley, PD et al. (n-3) PUFA alter raft lipid composition and decrease epidermal growth factor receptor levels in lipid rafts of human breast cancer cells. J Nutr. 2007;137:548-53.

[5] Berquin, IM et al. 2007.

[6] Berquin, IM et al. 2007.

[7] Jourdan, ML et al. Increased BRCA1 protein in mammary tumours of rats fed marine omega-3 fatty acids. Oncol Rep. 2007;17:713–9.

[8] Chen, J et al. Dietary flaxseed enhances the inhibitory effect of tamoxifen on the growth of estrogen-dependent human breast cancer (mcf-7) in nude mice. Clin Cancer Res. 2004;10:7,703–11.

[9] Kontogiannea, M et al. omega-3 fatty acids decrease endothelial adhesion of human colorectal carcinoma cells. J Surg Res. 2000;92:201–5.

[10] Iigo, M et al. Inhibitory effects of docosahexaenoic acid on colon carcinoma 26 metastasis to the lung. Br J Cancer. 1997;75:650–5.

[11] Bartoli, GM et al. n-3 PUFA and alpha-tocopherol control of tumor cell proliferation. Mol Aspects Med. 1993;14:247–52.

[12] Aronson, WJ et al. Modulation of omega-3/omega-6 polyunsaturated ratios with dietary fish oils in men with prostate cancer. Urology. 2001;58:283–8.

[13] 11Rhodes, LE et al. Effect of eicosapentaenoic acid, an omega-3 polyunsaturated fatty acid, on UVR-related cancer risk in humans. An assessment of early genotoxic markers. Carcinogenesis. 2003;24:919–25.

[14] Berquin, IM et al. 2008.

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