A diet that is high in either red meat or sugar, or both, increases the growth in the colon of bacteria called Fusobacterium nucleatum that appears to suppress a person's immunity to increase the growth of cancer cells in the colon. A prospective study of 137,217 adults followed for about 30 years shows that people who ate a lot of red meat and/or sugar were more likely to develop colon cancers that contained bacterium called Fusobacterium nucleatum. People who developed colon cancer and ate a primarily plant-based diet with lots of fiber were more likely to have cancers that did not have that bacterium attached to it (JAMA Oncol, published online January 26, 2017).
Foods You Eat Determine Which Bacteria Grow in Your Gut
Your diet determines which types of bacteria live in the first part (right side) of the colon. Bacteria that live in the last part (left side) of your colon receive food that has already been changed by the bacteria that live in the first part of the colon. The food that you eat must be broken down into its basic building blocks before it can be absorbed into your bloodstream. Carbohydrates must be broken down into single sugars, proteins into amino acids and fats into fatty acids. Foods that are not broken down to be absorbed in the small intestines pass along to reach your colon. There, bacteria can break down some of these foods that you could not absorb and use them to supply their energy. Bacteria that cannot break down the food that you eat will not thrive there. That means that bacteria in the right first part of your colon are the ones that grow and thrive on the non-absorbable food that you have eaten. Bacteria in the left (last) part of your colon get food that has already been changed by bacteria in the right (first) part.
The researchers examined healthy and cancerous tissue from 120 people taken during colonoscopies, where small pieces of tissue are removed to look for malignant changes in the inner linings of the colon. They found biofilms in 89 percent of tumors removed from the right colon (the first part), and in only 12 percent of tumors removed from the left side of the colon (the last part). Dense bunches of bacterial biofilms are found on most colon polyps and colon cancers. That means that in the future doctors will be able to check you for developing colon cancer long before it would normally be detected. Most colon cancers develop over five to ten years, and colon cancer is usually a curable disease if it is diagnosed early enough (CA Cancer J Clin, May-Jun 2008;58(3):130-60).
People who have dense biofilm colonies of bacteria in the right (first) part of the colon are five times more likely to have malignant colon cancer and pre-malignant colon polyps, compared to those who have no large biofilm colonies (Proceedings of the National Academy of Sciences, Dec. 16, 2014). The authors used a fluorescent technique to stain biopsy specimens for bacterium. In humans, a bacterial biofilm is a mucilaginous coating that bacteria secrete around themselves to protect them from attack by your immune system so they can live permanently inside your body. Other examples of biofilms include dental plaques in the mouth and the slime that covers stagnant pools or standing water.
How Diet May Cause Colon Cancer
Since bacteria in your colon eat the same food that you eat and passes to your colon, what you eat determines which bacteria grow in your colon. Certain bacteria such as Fusobacterium are associated with increased risk for colon cancer as evidenced by studies that show that a low-plant-fiber diet and lots of red meat are associated with the type of bacteria that attach to colon cancer cells. They have also been shown to increase risk for colon cancer by interfering with a person's immune system that is supposed to seek out and kill cancer cells. Studies show that Fusobacterium increase markedly in the stool after people switch from a high plant diet to one loaded with sugar and red meat.
Survival Rates After Colon Cancer is Diagnosed
Right-sided colon cancer is far more likely to kill than left-sided colon cancer. Patients with advanced colon cancer on the right side survived an average of 19 months, compared to patients with tumors on the left side 33 months (PLoS ONE, Dec 6, 2016;11(12):e0167540). Bacteria in your right colon eat the same food that you do. Bacteria in your left colon eat a different diet: what's left over from what the right-side bacteria ate. People with colon cancer may increase their chances for survival by following a healthful plant-based diet (BMC Cancer, Jan 30, 2017;17:83).
How Sugar May Increase Colon Cancer Risk
Many studies have shown that colon cancer is more common in people who are overweight. A new study shows that normal-weight people with markers of high blood sugar called metabolic syndrome are at more than double the risk of developing colon cancer (Cancer Epidemiology, Biomarkers & Prevention, Feb 2017). Markers of metabolic syndrome include:
• pinching more than two inches of fat under the skin around the navel
• systolic blood pressure over 120 at bedtime
• triglycerides over 150, blood sugar over 140 one hour after eating
• HDL cholesterol under 40
Link Between Meat and Colon Cancer
The World Health Organization (WHO) reported that eating processed meats and meat from mammals increases the risk of colorectal cancer (J Gastroenterol, Dec 2, 2016). Many other studies also show an association between meat and colon cancer (British Medical Bulletin, Dec 23, 2016; J Hum Nutr Diet, Jun 14, 2016; Br Med Bull, Dec 18, 2016). Processing meat increases the risk and some cooking methods increase risk more than others: meats cooked without browning had a lower increased risk while grilled, griddled or barbecued meats had the highest risk (European Journal of Nutrition, Nov 24, 2016). An earlier extensive review of the world's medical literature showed that eating red meat is associated with a 28-35 percent increased risk for developing colorectal cancer, while eating processed meats is associated with increased risk of 20-49 percent (Rev Esc Enferm USP, Feb 2012;46(1):234-9).
Researchers have proposed many possible mechanisms for the association between colon cancer and eating mammal meat, but there is no agreement at this time (Mol Aspects Med, Oct 2016;51:16-30). Proposed causal factors have included:
• TMAO (trimethylamine-N-oxide)
• certain bacteria in the colon
• high salt intake
• saturated fat
• environmental pollutants
• polycyclic aromatic carcinogens formed from high temperature cooking methods
• chemicals such as nitrates added to meats during processing
• heme iron
• Neu5Gc, a sugar-protein found in mammal meat
• possible infectious agents (not yet identified)
The recent research on types of gut bacteria attached to colon cancers suggests that this may be the most likely explanation for the long-observed association between meat and colon cancers. We await further research.