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Fish Oil May Curb Onset of Colorectal Cancer
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British study lends support to the anti-cancer potential of a key marine omega-3 found in fish oil

by Craig Weatherby

There's been good reason to suspect that fish might help curb the development of colorectal (bowel) cancer. Studies in cells and animals have shown that the marine omega-3s in fish oil tend to slow abnormal cell growth and help ensure that damaged or cancerous cells die spontaneously: a natural process known as apoptosis.

And we’re seeing an increasing amount of human research that supports the anti-cancer potential of marine omega-3s. For example, we ran a story last fall titled “Fish Cuts Risk of Colorectal Cancer, Red Meat Raises It” (Issue # 43, October 3, 2005).

Key Points

  • Results of a new clinical trial show that one of the omega-3s in fish oil (EPA) can slow the growth of precancerous polyps.
  • Findings bolster previous human, test tube, and animal research.
  • Un-distilled fish oils like ours may offer an omega-3-absorption edge.

That article reviewed the encouraging results of a huge, five-year population study designed to detect any strong

connections between diet and colorectal cancer. After adjusting for various risk factors, it appeared clear to the researchers that eating fish reduces the risk of colorectal cancer, while red and processed meats raises the risk.

These findings vindicated indications from test tube and animal studies suggesting omega-3s discourage the development of colorectal cancers, and bolstered the modest amount of omega-3-supportive evidence from prior population studies.

New findings support cancer-prevention potential of fish oil

Roger Leicester, M.D.—a bowel cancer surgeon at St George’s Hospital in Tooting, South London—led the new clinical study. His team’s goal was to test the hypothesis that supplements unusually rich in EPA—one of the two long-chain marine omega-3 fatty acids in fish and fish oil—is primarily responsible for the apparent ability of dietary fish and fish oil to reduce bowel cancer risks.

They knew that fish and fish oil possess anti-cancer properties, but prior experiments using DHA alone had not proven that it could inhibit the progression from polyps to cancer in a consistent fashion.

Is fish oil a viable alternative to Vioxx?

Most researchers believe that inflammation plays a critical role in the process that transforms benign bowel and prostate growths in to killer cancers. This is why research results indicate that two kinds of anti-inflammatory drugs—aspirin and so-called “COX-2 inhibitors (e.g., Vioxx and Celebrex)—seem to help prevent both kinds of cancer.

Both of these two classes of drugs work their inflammation-related anti-cancer effects by impairing the functioning of one or more of two key, pro-inflammatory metabolic proteins called the COX-1 and COX-2 enzymes. Aspirin is believed to primarily block the COX-1 enzyme, while Vioxx, Celebrex, and related drugs block the COX-2 enzyme.

In addition to dietary changes designed to reduce inflammation—more fish and vegetables, less red meat—it is now believed that blocking the COX-2 enzyme may be one of the most effective ways to prevent colorectal and prostate cancers.

Accordingly, doctors have been looking to COX-2 inhibitors to help in the preventive fight. But as we all know from recent headlines, these drugs have been linked to increased cardiovascular risks, and for this reason some, notably Vioxx, have been withdrawn.

The safety concerns surrounding synthetic COX-2-inhibiting drugs have prompted researchers to seek safer ways to prevent excessive, pro-inflammatory activity by the suspect enzyme. And it’s looking like the omega-3 EPA in fish oil is a leading candidate to replace these expensive, seemingly risky drugs.

This is not terribly surprising, since the transformation of benign bowel polyps into cancerous tumors is preceded by inflammation-induced and -facilitated changes in cells. And it appears that of the two major omega-3s in fish oil, EPA exerts the strongest anti-inflammatory effects, by inhibiting gene-induced “expression” of the COX-2 enzyme. Since the COX-2 enzyme facilitates production of pro-inflammatory prostaglandins (ephemeral hormone-like chemicals) from dietary and bodily omega-6 fatty acids, dietary EPA can dampen cancer-promoting inflammation (See the "Vioxx” sidebar, below).

For the St George’s study, 30 patients with a history of sporadic polyps were recruited and randomly assigned to receive either purified EPA capsules for three months, or no treatment.

Small samples of the lining of the colon were taken before the start and at the end of the three month trial, which allowed the researchers to measure how quickly new cells were proliferating, and the rate at which cells were being removed via apoptosis.

The St. George's study showed three important findings:

  • The rate at which bowel-lining cells formed (proliferation) fell by almost 25 percent in the subjects who took the EPA capsules, compared to those who received no treatment.
  • The rate at which cells were eliminated by apoptosis more than doubled in the patients who took the EPA capsules, and there was no significant change in the untreated control group.
  • The levels of EPA in the cells of the treated participants were twice as high as in the control group.

Note: The capsules were unusual in that they contained only EPA, at levels far higher than those found in standard, distilled fish oil capsules, or in our natural, un-distilled Sockeye Salmon Oil capsules. In addition, the capsules used in the study were “enteric-coated”, to ensure that the EPA did not leave the capsules until they reached the small bowel.

However, as explained below (see "Could unrefined fish oil offer a vital advantage?"), Dr. Leicester believes that the triglyceride form of EPA in his test capsules—and in our Sockeye Salmon Oil capsules—may offer a cell-uptake advantage over the ethyl ester form in standard fish oil capsules. This distinction may explain why eating whole fish—whose omega-3s generally occur in the triglyceride form—appears to confer protection from bowel cancer.

The St George’s team plans to conduct two follow up clinical trials:

  • A six-month investigation will examine the effects of different doses of EPA in patients with a history of polyps.
  • Another study will investigate whether EPA can reduce polyp growth in patients with an inherited condition called familial adenomatous polyposis, in which large numbers of polyps form in the gastro-intestinal tract, which raises the risk of bowel cancer greatly.

Dr. Leicester believes that supplemental EPA may also help patients with Crohn’s disease and ulcerative colitis. Many of the anti-inflammatory drugs used to treat these and other inflammatory conditions have serious, sometimes fatal, side effects (See the sidebar at right).

Could unrefined fish oil offer a vital advantage?

Dr. Leicester now supports the use of marine omega-3s for reducing the risk of bowel cancer: “I am fairly confident that EPA can prevent re-occurrence of bowel cancer polyps in patients who already have them. Our initial results were very significant. We think fish-oil capsules could eventually be given as a preventative treatment against cancer. Any fish diet, but particularly oily fish, which are high in omega-3s, will help prevention.”

And he had this to say during a radio interview on London’s “LBC News 1152 Morning Report.” One comment in particular (underlined for emphasis) caught our attention:

  • “If you look at animal work on colon cancer, we see that omega-3s slow the growth of polyps. Bowel cancer always starts as a polyp, and it take about ten years to develop in to cancer, so we have very long period to try to stop it.”
  • “We know that people who eat a lot of oily fish have a lower incidence of bowel cancer… there is almost no bowel cancer in Eskimos, whose diet is mostly fish, and in the Far East, populations who eat a lot of fish and little meat have about half the incidence of bowel cancer.”
  • “Animal work shows that the polyps grow as a result of increased cell production and decreased cell death. Cells normally die after a time, except in cancer. We showed that EPA could reverse that trend, so that’s encouraging… [but] many of these products [i.e., standard fish oils] contain other fats called ethyl esters, which prevent incorporation of EPA into cells.”

If true, Dr. Leicester’s comment concerning the metabolic deficiencies of the ethyl ester forms of EPA and DHA is significant and startling. (We'll need to explore this further.) Standard fish oils undergo molecular distillation to remove almost everything from the oil but the omega-3s and small amounts of other fatty acids. But molecular distillation also converts the EPA and DHA in the source fish oils from their natural triglyceride from into the ethyl ester form.

Fortunately, any metabolic defect of the ethyl ester omega-3s (EPA and DHA) in standard fish oils would have no bearing on Vital Choice customers who take our wholly natural and un-distilled Sockeye Salmon Oil, in which EPA and DHA occur in their natural triglyceride forms.

What is colorectal (bowel) cancer?

Colorectal (bowel) cancers affect the large bowel and the rectum. When colorectal cancers are diagnosed early the odds of a complete cure are excellent. But untreated, they can protrude into the lining of the bowel, invade adjacent organs, and eventually spread throughout the body.

Signs of colorectal cancer include changes in bowel habits, bleeding from the rectum, dark, bloody stools, inexplicable weight loss, or unusual fatigue.

The highest rates are seen in upper-income urban areas, possibly because studies in various countries have shown a direct relationship between deaths from colorectal cancer and higher consumption of calories, meat protein, and dietary fats, which are characteristic of diets in relatively affluent populations.

Populations with high-fiber diets enjoy lower rates of colorectal cancer, possibly because such diets yield more frequent, bulkier bowel movements. This would reduce the amount of time digested food remains in the gut, thus diluting the effect of any cancer-causing agents. However, this hypothesis remains unproven.

Like most cancers, colorectal cancers are characterized by abnormally rapid, disorderly production of cells. They usually start as wart-like growths known as colorectal polyps, which may or may not become cancerous, depending largely on one’s diet, lifestyle, and genetic makeup.

One in 10 people over 60 have colorectal polyps, but few become cancerous malignancies. If detected early, polyps can be removed safely without a need for serious surgery. This is why it is smart for people over the age of 50 to undergo a colonoscopy every three years. 


  • LBC News 1152 Morning Report. Accessed online July 20, 2006 at
  • S.L.A. Pharma AG  Development status: Clinical research on ALFA © 2006 Accessed online July 20, 2006 at
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  • Yoon H, Benamouzig R, Little J, Francois-Collange M, Tome D. Systematic review of epidemiological studies on meat, dairy products and egg consumption and risk of colorectal adenomas. Eur J Cancer Prev. 2000 Jun;9(3):151-64.
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