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Fish Cuts Risk of Colorectal Cancer, Red Meat Raises It
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indings add to anti-cancer evidence for omega-3s; meat marketers blur the prevention picture

by Craig Weatherby

While many fear cancer as a disabling, potentially fatal disease, Americans’ awareness of the risk factors for colorectal cancer—one of the most common killer cancers—is woefully distorted, according to the results of a survey conducted by the American Institute for Cancer Research (AICR) and released in August of this year.

This ignorance persists despite the high-profile awareness campaign conducted by Katie Couric, co-host of NBC-TV's "Today" show (pictured at left), whose husand died from colorectal cancer at the age of 42.

The title of the press release announcing the survey results—“Americans’ Awareness of Meat-Cancer Link Drops Significantly”—underscores the importance of publicizing the European research findings detailed in this article.

European researchers conducted a huge study in 10 countries, designed to determine the strength of previously reported links between red meat and risk of cancer (cancer of the colon or rectum).

The study involved almost half a million people (478,040) who were cancer-free when they enrolled in the study.  The researchers collected information on diet and lifestyle, and, after about five years, 1,329 had been diagnosed with colorectal cancers.

The team then examined the dietary intakes of red and processed meat, poultry, and fish among the 1,329 cancer patients to reveal any statistically significant links. To isolate the cancer-risk effects of these four common protein sources, the scientists employed a “proportional hazards” model that adjusted for differences in colorectal cancer risk linked to age, sex, caloric intake, height, weight, smoking status, intake of dietary fiber and folate (folic acid), alcohol consumption, and other factors.

Findings give fish a boost, while red meat gets the boot

In the end, the results were clear. Fish reduced the risk of colorectal cancer, while red and processed meats raised it.

Colorectal cancer risk rose in tandem with increasing daily intake of red and processed meat, with the lowest risk seen when people ate less than one ounce per day, and the highest risk seen in people who ate about six ounces per day.

In contrast, the risk of colorectal cancer decreased as fish intake increased. The lowest risk was seen in people who ate the most fish (just under three ounces per day), while the smallest preventive benefit was seen among those who ate the least fish in the survey (less than one-third ounce per day).

Poultry did not appear to affect the risk of colorectal cancer one way or the other, possibly because its fatty acid profile ranges somewhere between those of red meat and fish, depending in part upon the feed a commercially raised chicken, turkey, or duck receives.

We should note that grass-fed beef—as opposed to the grain-fed beef that dominates the market—offers a higher ratio of omega-3s to omega-6s, and should therefore offer a safer alternative. The exact ratio of omega-6 fatty acids to omega-3 fatty acids depends on the duration of grazing (versus time spent eating grain in feedlots) and the type of pasture.

On average, conventional beef typically offers a reasonably healthy 4:1 omega 6:3 ratio while grass-only diets produce a more optimal 2:1 omega 6:3 ratio.  In addition, grass-fed beef have less saturated fat in relation to omega-3 and omega-6 polyunsasturated fats, which is beneficial for heart health.

Omega-3s likely deserve the anti-cancer credit

Why would fish reduce the risk of colorectal cancers?  The long-chain omega-3 fatty acids abundant only in fish seem the likely heroes.  As the authors of a Swiss review article from 2004 put it, “…n-3 PUFAs [omega-3s] act at different stages of cancer development and through several mechanisms... As a result, n-3 PUFAs [omega-3s] limit tumor cell proliferation, increase apoptotic [cancer-call suicide] potential… promote cell differentiation and possibly limit angiogenesis. “The modulatory actions of n-3 PUFAs [omega-3s] on the immune system and their anti-inflammatory effects might also play a role in reducing colon carcinogenesis… it appears that n-3 PUFAs may be of use in colon cancer prevention.”

Diet and colorectal cancer

Colorectal cancer is considered one of the most preventable types, and diet plays a major role in reducing or raising the risk. To quote from a recent review article by noted cancer expert Edward Giovannucci, MD, ScD, of Harvard Medical School, “Although many mechanisms remain unclear, a large body of evidence indicates that several dietary and lifestyle factors are likely to have a major influence on the risk of colon cancer.… At least 70% of colon cancers may be preventable by moderate changes in diet and lifestyle.”

Dr. Giovannucci echoes the authors of other recent reviews in identifying these factors:

Risk-raising factors for colorectal cancers

  • Excess dietary calories
  • Red and processed meats
  • Refined carbohydrates
  • Hyper-insulinemia (chronically elevated blood insulin levels, caused by obesity and diets high in saturated fats and refined carbohydrates)
  • High alcohol consumption in combination with a diet low in folate and methionine

Risk-reducing factors for colorectal cancers

  • Fish (due to their omega-3 content)
  • High-fiber grains, beans, fruits and vegetables (the protective factor in these foods may be nutritional factors such as antioxidants, rather than fiber itself)
  • Folic acid (a B-vitamin)
  • Methionine.  This amino acid acts as an antioxidant, helps remove fat from the liver, and controls levels of anti-cancer sulfur compounds in the body.  Meat, fish, and dairy products are the richest sources of methionine. Small amounts occur in fruits, vegetables, vegetable juices, fermented foods, and whole grains.

Meat marketers distort the picture

The latest survey by the American Institute for Cancer Research (AICR) shows an alarming downward trend in public awareness of the risks posed by red meat.

Why is the public increasingly unaware of the meat-cancer link?  According to the AICR press release announcing the survey results, experts point to the recent popularity of high-protein, meat-focused diets (e.g., Atkins), and the efforts of meat marketers to downplay the health risks of red meat by emphasizing that lean cuts are “heart-healthy”.  But the AICR’s experts say that even lean red meat poses cancer risks.

Who is at risk?

According to the Centers for Disease Control and Prevention (CDC), colorectal cancer is the second leading cause of cancer-related deaths in the United States. The American Cancer Society estimates that 56,730 Americans will die of colorectal cancer this year. Colorectal cancer is also one of the most commonly diagnosed cancers in the United States; approximately 146,940 new cases were diagnosed in 2004. Colorectal cancer is the third most common cancer in men and in women.

The risk of developing colorectal cancer increases with advancing age, with more than 90% of cases occurring in persons aged 50 years or older. Other risk factors include inflammatory bowel disease, a personal or family history of colorectal cancer or colorectal polyps, and certain hereditary syndromes. Lifestyle factors that may contribute to increased risk of colorectal cancer include lack of regular physical activity, low fruit and vegetable intake, a low-fiber and high-fat diet, obesity, alcohol consumption, and tobacco use.

Early detection is key

After making diet and lifestyle changes, people can reduce the risk of death from colorectal cancer by getting exams that detect and removing precancerous colorectal polyps, and by getting treatment in the cancer's early stages.  Colorectal cancer can be prevented by removing precancerous polyps or growths, which can be present in the colon for years before invasive cancer develops.

The CDC recommends getting any one of four tests for colorectal cancer screening. (Note: digital rectal examinations are the least reliable because they inspect a very limited area.):

  • Flexible sigmoidoscopy exams reduce risk of death from cancers located within reach of the sigmoidoscope by 59 to 79 percent.
  • Fecal occult blood test (FOBT) screening every other year reduces risk of colorectal cancer death by 15 to 18 percent.
  • Double-contrast barium enema test.
  • Colonoscopy exams can be used as screening tests or as follow-up diagnostic tools when the results of another screening test are positive.

Experts recommend regular screening for all adults aged 50 years or older, as follows:

  • FOBT every year.
  • Flexible sigmoidoscopy every five years.
  • Double-contrast barium enema every five years.
  • Colonoscopy every 10 years.

Persons at higher risk should begin screening at a younger age and may need to be tested more frequently.


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