However, there are many different types of nutrients in vegetables that are protective, so it is probably not one single nutrient but the combination of nutrients working together that has protective effects.
Calcium. At least two studies have found that consuming at least 1200 milligrams of calcium per day — either in the form of supplements or supplements and food — for several years reduces the risk of developing colorectal adenomas. Calcium binds bile and fatty acids in the colon, which decreases exposure to carcinogenic chemicals. Dairy products, such as milk, cheese, and yogurt are good sources of calcium, but full-fat varieties are also high in saturated fat. When consuming dairy products, choose low-fat cheese, skim or 1% milk, and low-fat or nonfat yogurt.
Omega-3 fatty acids. Omega-3 fatty acids found in fish and some nuts and seeds decrease the inflammation associated with the initial stages of colon and other cancers.
Folate and alcohol. Folate, also called folic acid, is a B vitamin and is combined with vitamins B6 and B12 for healthy cell development. A diet low in folate can lead to precancerous cells. Since there is a rapid turnover of cells in the colon, and therefore a greater need for folate in these cells, a low folate intake is a risk factor for colorectal cancer. Folate is found in dark-green, leafy vegetables such as spinach and turnip greens, citrus fruits and juices, and dried beans and peas. Since 1996, the Food and Drug Administration has required that folic acid be added to enriched breads, cereals, flours, pasta, rice, corn meals, and other grains.
Alcohol interferes with folate metabolism, so heavy drinkers have an increased need for folate. In fact, people who have a diet low in folate and high in alcohol have an increased risk of colorectal adenomas. People who are heavy beer and liquor drinkers have been shown to have an increased risk of colorectal cancer, while those who drink wine have a decreased risk. It is recommended that beer and liquor be limited to no more than one drink a day. Getting enough folate can also help to prevent polyps from reoccurring.
Vitamin D. Vitamin D is a fat-soluble vitamin that is synthesized in the skin by sunlight and is found in some foods. There is some evidence that high blood levels of vitamin D have a protective effect against colorectal cancer. Good food sources of vitamin D include salmon, sardines, mackerel, and other fatty fish. Milk has been fortified with vitamin D since the 1930’s to prevent rickets.
Normally, exposure to sunlight provides the body with all of its vitamin D needs. However, in the northern parts of the United States, sun exposure in the winter months does not supply enough skin synthesis of vitamin D. Cloudy days, use of sunscreen, and shade also decrease skin synthesis. Perhaps not surprisingly, there is a higher incidence of colorectal cancer in the North than the South. Older people also do not synthesize vitamin D in the skin as effectively as younger people.
Vitamin D helps to absorb calcium during the digestive process, so taking a multivitamin containing vitamin D is recommended for adults over 50, people who live in northern latitudes, and people who get limited sun exposure for any reason.
Fiber. The link between dietary fiber intake and colorectal cancer is controversial. While many studies have been done on the effects of fiber consumption on colorectal cancer, the findings have been inconsistent.
It has been suggested that the inconsistency comes from the type or source of fiber being studied. There are two types of fiber: soluble and insoluble. Both types of fiber come from plant foods. Fruits and vegetables, which contain both soluble and insoluble fiber, appear to have the most benefit, while wheat fiber, which is primarily insoluble, and psyllium, which is about 70% soluble and 30% insoluble, do not seem to provide protection against colorectal cancer.