Colorectal Cancer: Nutritional Considerations

Diet appears to be a major contributor to colon cancer risk. Several lines of evidence implicate meat (especially processed red meat) in colon cancer risk. The association is presumed due to macronutrients (such as saturated fat) found in meat products, as well as to carcinogens found in or formed by cooking or processing of meats. Plant–based and vegetarian diets are associated with a much lower incidence of colon cancer,⁴ probably due to the absence of meat and the inclusion of protective plant constituents.

Dietary Factors Associated with Increased Risk

Meat products. Higher intake of processed red meat, in particular, appears to increase the risk for distal colon (rectal) cancer, presumably due, at least in part, to its nitrosamine content⁵ or to the presence of polycyclic aromatic hydrocarbons (PAH), known mutagens and suspected carcinogens that are formed as a result of charbroiling.⁶ Heme iron found in meat is also associated with proximal colon cancer⁷. This association has been explained by the formation of cytotoxic compounds in the intestinal lumen.⁸ In the European Prospective Investigation into Cancer and Nutrition (EPIC) study, individuals eating > 160 g/day of red or processed meat had a 70% greater risk for colorectal cancer than persons eating < 10 g/day.⁹ The Cancer Prevention Study II (CPS II) Nutrition Cohort considered long–term consumption of meat in determining colorectal cancer risk and determined that individuals eating the highest amount of red meat and processed meat were at 50% greater risk for colon cancer, compared with those eating the lowest amount. Eating the highest amount of red meat also appeared to increase the risk for rectal cancer by 70% when compared with the lowest level of consumption.¹⁰

Although white meat may carry a lower risk than red meat, Adventist men who ate white meat >1 time per week had a risk roughly 3.3 times that of those who abstained from eating white meat.¹¹ This may be due to the presence of mutagenic heterocyclic amines (HCAs), which are found in chicken as well as other meats.¹²

A high cholesterol intake,¹³ higher serum cholesterol,¹⁴ and higher levels of oxidized LDL¹⁵ are also associated with greater colorectal cancer risk. High–cholesterol foods such as eggs may also increase risk of proximal colon cancer.¹⁶

Alcohol. Several studies show that alcohol consumption (> 1 drink per day) is independently associated with the risk of colorectal adenoma or cancer.¹⁷

Dietary Factors Associated with Decreased Risk

Fiber. Studies on dietary fiber and colorectal cancer risk have yielded conflicting findings. The best evidence for the role of fiber relates to its apparent ability to reduce the risk of adenomatous polyps, a precancerous lesion.^18–20 Some research also shows a reduced risk for polyp recurrence in women who follow a high–fiber, low–fat diet or a fiber–supplemented, vitamin–enriched diet.^21,22 The largest study to date, however, found that the reduction in colorectal cancer risk associated with high dietary fiber intake was small (6%) and not statistically significant.²³

The possible preventive effect of fiber–containing foods may come from an association with micronutrients, including carotenoids,²⁴ sulfur compounds in garlic,^16,25 or glucosinolates found in Brassica vegetables,²⁶ which accelerate Phase II detoxification of potential carcinogens. Data show that men who eat the most fiber–depleted refined carbohydrates (eg sucrose, refined starches) have roughly twice the risk for developing colon cancer as men who eat the least amount.^27,28 Results for women have not been established.²⁹ This risk is attributed to the high glycemic load these foods carry³⁰ and their tendency to increase blood concentrations of insulin–like growth factor,³ a known risk factor for many cancers.

Folic acid and vitamin B6. Leafy green vegetables, beans, and whole grains are good sources of folate, an important determinant of DNA methylation that affects maintenance of DNA integrity and stability.³¹ Although a relationship among folate and other dietary factors may account for benefits, evidence indicates that individuals eating the most folate have a 39% lower risk for colon cancer³² and a 25% lower risk for colorectal cancer than persons eating the least folate.³³

Similarly, vitamin B6 is involved in DNA methylation, and it suppresses tumorigenesis by reducing cell proliferation, oxidative stress, angiogenesis, and other mechanisms.³⁴ Individuals who consume the highest amounts of vitamin B6 or have the highest blood concentrations of pyridoxal phosphate have a 34% to 44% lower risk for colorectal cancer, compared with those who have the lowest intakes or blood levels.^3,35

Vitamin E, vitamin D, and calcium. Some evidence suggests that eating one–fourth of an ounce of nuts each day may protect against colorectal cancer, particularly in women.³⁶ The lower risk is attributable to food (not supplemental) sources of vitamin E, higher intakes of which appear to reduce risk by 63% to 84% in persons younger than 65 years.³⁷

Calcium may be a double–edged sword, reducing risk of colon cancer but increasing risk of prostate cancer with high intakes.³⁸ Research found a lower risk for colon cancer in persons whose calcium intake was 700 mg per day, compared with those who have lower intakes; beyond this amount, benefit was minimal.³⁹ Higher intakes of both calcium and vitamin D are associated with lower risk for colorectal cancer,⁴⁰ and supplemental forms of calcium and vitamin D may be inversely associated with recurrence of colorectal adenoma.⁴¹

Calcium can bind bile acids that may act as mutagens in the colon, and vitamin D may act as an anticarcinogen through regulation of growth factor and cytokine synthesis and signaling, modulation of the cell cycle, apoptosis, and differentiation.⁴²

Orders

See Basic Diet Orders chapter.

Smoking cessation.

Exercise prescription.

What to Tell the Family

Colon cancer risk may be reduced through healthful diet and lifestyle measures. These include avoiding overweight, following a plant–based diet, choosing micronutrient–rich foods, and limiting alcohol use.