A study published this week shows that vegetarians who eat fish have a 43 percent reduced risk for developing colon cancer, compared to people who eat meat (JAMA Internal Medicine, March 9, 2015). Researchers analyzed the diets of nearly 78,000 men and women. During an average seven years of follow-up, they identified 380 cases of colon cancer and 110 cases of rectal cancer. Compared to people who ate meat,
• Vegetarian plus fish had 43 percent lower risk
• Vegetarians: 22 percent lower risk
• Vegetarians plus milk and eggs: 18 percent lower risk
• Vegans (no animal products): 16 percent lower risk
Many other studies have shown that you are at increased risk for colon cancer if you:
• eat a lot of red meat, processed meats, fried foods, sugared drinks, sugar-added foods and other refined carbohydrates such as bakery products
• do not eat a lot of fruits, vegetables, whole grains, beans, nuts and other seeds
• are overweight
• do not exercise
• drink alcohol
• lack vitamin D
Your risk increases if you have:
• colon polyps,
• inflammatory intestinal conditions such as ulcerative colitis or Crohn’s disease,
• inherited syndromes (familial adenomatous polyposis),
• family history of colon cancer and polyps,
• uncontrolled diabetes with high sugar and insulin levels,
• radiation therapy for any cancer, or
• you have had your gall bladder removed
Why Fish May Offer Extra Protection
Most fish contain omega-3 fatty acids that slow down inflammation, and vitamin D that helps protect against cancers. Your immunity is supposed to kill germs and protect you from infections. However, your immunity is supposed to slow down as soon as the infection is gone. If your immunity stays on all the time, it is called inflammation which increases cancer risk. This latest study is just one of many that have suggested that eating fish helps to prevent colon cancer. However, none of the studies on fish oil pills have shown any added protection.
How Meat May Cause Colon Cancer
Here is a mechanism that could explain why colon cancer is associated with eating too much red meat and animal fat, and too little of the foods from plants (Science, May 17, 2002). Your liver removes breakdown products of metabolism from your body and concentrates them into a liquid called bile. Then bile passes through a tube leading from the liver to the gall bladder, a balloon that stores the bile. When you eat, the gall bladder contracts and squeezes bile through a tube leading into your intestines, where the bile mixes with the food that you have eaten and breaks down the fat into building blocks called monoglycerides, fatty acids and glycerol that can be absorbed into you bloodstream.
Eating a high-meat diet causes your liver to make more bile, and bile is full of a chemical called lithocholic acid, a bile acid that helps digest fat. Lithocholic acid is probably the most toxic compound that your body makes. Lithocholic acid damages the DNA, the genetic material in cells. Giving animals high concentrations of lithocholic acid causes colon cancer (Wiener Medizinische Wochenschrift, October 2008;158(19-20):539-541). However, giving these same animals large doses of vitamin D prevents lithocholic acid from causing colon cancer.
Previous research shows that people who develop colon cancer have high concentrations of lithocholic acid in their intestines. This may explain why people who have had their gall bladder removed are at increased risk for colon cancer. Your gall bladder is supposed to squeeze bile into your intestines only after you eat. When you have your gall bladder removed, bile flows continuously from your liver into your intestines 24 hours a day. This continuous exposure to bile acids, and lithocholic acids in particular, may cause colon cancer.
How Refined Carbohydrates Contribute to Colon Cancer
Cancer of the colon is associated with eating a lot of refined carbohydrates found in sugared drinks, sugar-added foods, bakery products and pastas. These foods cause a high rise in blood sugar that causes your pancreas to release large amounts of insulin and Insulin-Like-Growth-factor-1. Both of these hormones increase cancer risk by increasing cell growth. Furthermore, refined carbohydrates in bakery products and pastas are constipating which prolongs contact between food and the inner surface of the colon (Cancer Epidemiology Biomarkers & Prevention, 2001;10(7):725-731). Whole grains appear to help prevent colon cancer by sweeping foods and carcinogens through the colon at a faster rate.
How Plants May Help to Prevent Colon Cancer
Grains, beans, fruits and vegetables contain resistant starches that can help to prevent colon cancer (American Journal of Gastroenterology, 2000;95(4);1017-1020). Carbohydrates are just single sugars or chains of sugars. Before any carbohydrate can be absorbed into your bloodstream, it must first be broken down into single sugars by enzymes and bacteria in your gut. Resistant starches cannot be digested in the intestines, so they pass to the colon where bacteria break them down into short chain fatty acids that may help to prevent cancers, particularly colon cancer. Many people avoid the foods that contain resistant starches because they are the most common cause of intestinal gas, which is produced by the fermentation of unabsorbed carbohydrates by bacteria.
What This Study Means for You
Colon cancer appears to be primarily an environmental disease, so you should try to avoid the factors that are associated with increased risk. This means that you should eat large amounts of fiber-rich foods including fruits, vegetables, whole grains, beans, nuts and other seeds; limit or avoid red meat and processed meats, bakery products, sugared drinks, sugar-added foods, fried foods and alcohol; exercise regularly and avoid being overweight. Do not smoke. Keep blood hydroxy vitamin D above 30 nmol/L. Do not have your gall bladder removed unless it is necessary.
Colon cancer is highly curable when it is diagnosed before it has spread, but the cure rate drops below 40 percent when it is diagnosed after it has spread. Therefore, people over the age of 50 should have a colonoscopy or barium enema X-ray at least once to check their colon for polyps (premalignant growths on the inner lining of the colon). If you have no polyps, no family history of colon cancer and no colon symptoms, many doctors believe that you do not need to be checked more often than once every ten or twenty years. However, if you have polyps, they should be removed.