WHOLE GRAINS AND REDUCED RISK OF CANCER

Cancer as reported is the second leading cause of illness and death in the United States claiming an estimated 550,000 lives each year, translated as more than 1,500 lives lost each day. The sad news, one third of these deaths are diet related.

As with CHD (cardiovascular Heart Disease), there is strong epidemiologic (epidemic diseases) evidence that the consumption of whole grains reduces risk of many types of cancer. The Diet & Health publication in 1989 showed a strong relationship between whole grains and certain cancers. Two of the cancers being discussed are:• Gastrointestinal and
• Hormone dependent cancers

Examination of Whole Grains & Gastrointestinal cancers The first meta-analysis of the relationship between whole grain intake and cancer was a preliminary review of studies. From these studies, five of them focused on colorectal cancer and seven focused on gastric cancer. In 16 of the 18 mentions of whole grain reduced cancer risk was found as high, compared to low intakes of whole grains.

Another meta-analysis of 40 studies followed and 20 different types of cancer examined, 46 of the 51 mentions of whole grain intake were associated with a decreased risk of cancer. This analysis showed the strongest association for gastrointestinal cancers. When they compared high versus low intakes of whole grain, the analysis showed a 21% lower risk for cancers of the colon and rectum, 30% lower for pancreatic cancer, and 43% lower risk for gastric cancer.

The third meta-analysis of whole-grain intake and cancer focused on 19 northern Italian studies, all used the same protocol. The researchers found a reduced risk of 18 different cancers in those who regularly ate whole grains. This association was graded by the amount of intake. For gastrointestinal cancers, the decrease in risk ranged from 20% to 50% for the highest versus the lowest level of whole grain food intake. The specific results for individual cancers were as follows:

• 50% lower risk for cancer of the stomach, colon and gallbladder
• 40%lower risk for cancer of the liver• 30% lower risk for cancer of the rectum
• 20% lower risk for cancer of the pancreas

Experimental studies of dietary fiber/whole grain and colon cancer are less favorable, though not definitive.One recent long-term experimental study found no association between increased consumption of bran and whole grains and recurrence of colon polyps. Another recent study investigating the effects of a high fiber and low-fat diet , found no effect on the recurrence of colon polyps. The relevance of these studies may not be essential because only 5% of colon polyps eventually become cancerous. The use of colon polyps as a marker for colon cancer continues the debate.

POTENTIAL BENEFITS OF WHOLE GRAIN

It is unclear which component(s) of whole grains is responsible for reducing cancer risk. Preliminary research suggests many mechanisms are responsible for the protective action of whole grains that includes carbohydrate fermentation, decreased transit time, increased fecal bulk, and antioxidant properties.

Review of Whole Grain Properties

Carbohydrate Fermentation Whole grains are rich sources of fermentable carbohydrates. These undigested carbohydrates are fermented in the colon and produce short-chain fatty acids (such as acetate, butyrate and propionate). These short-chain fatty acids lower colonic pH, reducing the ability of bile acids to act as carcinogens.

Decreased Transit Time & Increased Fecal Bulk Dietary fiber increases transit time and increases fecal bulk. It allows less time for fecal mutagens to interact with the intestinal epithelium (tissues that covers cavity). A study of 20 populations in 12 countries found that fecal weight was inversely related to colon cancer risks. Wheat bran and oat bran are components of whole grains that increase fecal weight most effectively. Dietary fiber may have the effect of binding or diluting bile acids. Bile acids are thought to promote cell proliferation, therefore allowing increased opportunity for mutations to occur and abnormal cells to multiply.

Antioxidant Effects The components of whole grains function as antioxidants. These are phenolic acids, vitamin E, selenium, lignans and phytic acids. Recent research indicates that whole grain foods are a rich source of antioxidants, comparable to most fruits and vegetables. The reason given, in addition to preventing LDL (harmful) oxidation, these antioxidants may also counter oxidative stress that causes acute and chronic cell injury including cancer formation.

Example Colonic bacteria produce significant amounts of oxygen radical which can override the antioxidant capability of intestinal epithelial cells. How this works, the dietary phytic acid may suppress this potential problem by chelating various minerals in the colon thereby suppressing the oxidative reaction. The same response is true of Vitamin E that has similar antioxidant properties in respect to cell membrane. It helps to conserve selenium by keeping it in its reduced state. In this process, selenium functions as a cofactor for glutathione peroxidase, an enzyme that protects against, oxidative tissue damage. At high levels selenium can also suppress cell proliferation.