Minerals and fiber can both be allies in the fight for cancer prevention. Still, the exact benefits that each brings is up for debate. In this section, we explore the ways in which fiber and minerals can be beneficial.
Selenium's Tight-Rope Act
Selenium is not actually an antioxidant. Rather, it is part of the enzyme glutathione peroxidase, which is part of the body's antioxidant defense system, helping protect it against free radicals. You don't hear as much about selenium, however, because we still don't know that much about it. Preliminary evidence suggests a link between selenium and a reduced risk for cancers of the lung, colon, and prostate.
Getting the right amount is a balancing act that Mother Nature handles fairly well. Selenium is widely available in such foods as grains, lean meat, poultry, and fish. There is a narrow margin, however, between safe and toxic amounts of selenium. So high-dose supplements are a distinctly bad idea.
The Calcium Connection
The evidence supporting this newcomer to the cancer-prevention scene is a bit less conclusive yet still promising. The research suggests calcium plays a role in reducing the risk for colorectal cancer, perhaps by thwarting the ability of cancerous cells to gain a foothold in the lining of the intestines or by binding with them, rendering them benign. Calcium-rich foods seem to offer more protection than calcium supplements.
Many Americans fall short of the recommended daily intake for calcium, which is 1,300 milligrams for teenagers; 1,000 milligrams for adults 19 to 50 years of age; and 1,200 milligrams for adults 51 years of age and older. Amounts of 1,200 to 1,500 milligrams have been linked to an anticancer effect. On the other hand, there is evidence that an intake of more than 2,000 milligrams of calcium per day, primarily from supplements, may increase the risk for prostate cancer.
In light of this, both men and women are best off meeting recommended levels of calcium primarily from food sources (since it's far more difficult to overdose on a vitamin or mineral when you get it from food than when you take supplements). Calcium sources include milk, yogurt, cheese, fortified juice, sardines with bones, salmon, and some leafy green vegetables (bok choy, broccoli, kale, and turnip and collard greens). If you obtain much of your calcium from dairy products, select low-fat or nonfat varieties to help keep your intake of total and saturated fat low. If you take a calcium supplement, consult with a registered dietitian or your doctor to determine how much is appropriate for you to take.
The research on fiber in the prevention of colon cancer is positive, even if the link is somewhat shaky. There are a variety of ways that fiber may protect: by diluting toxins, by altering conditions within the bowel, and by literally getting carcinogens out faster. The numerous variables are what confuse the issue. In fact, as more knowledge of fiber's potential actions has accrued, the link has become less clear.
This may be partly due to the failure of many past studies to separate out the effects of soluble versus insoluble fibers. It's the insoluble type -- as in wheat bran -- that probably provides the most protection. But other studies have also found a protective effect from fruits and vegetables, which are higher in soluble fiber. To confuse matters further, several large studies even found that overall fiber intake does not seem to have any significant effect on lowering colon-cancer risk. Fiber's effect also may depend on whether your diet is high in fat, too.
But don't mistake the forest for the trees. Because fiber is clearly beneficial to many other conditions, it's wise to make sure you are consuming adequate amounts. Furthermore, foods high in fiber are also known to contain other healthful substances that do have protective effects against cancer.
Experts advise aiming for 20 to 35 total grams of fiber each day. Most Americans, however, eat less than half this amount. If your diet is low in fiber, try gradually substituting foods made with whole grains for those made with refined grains, and work up to eating at least five servings of fruits and vegetables a day.
When you look at how to include more minerals and fiber to your diet, you also need to keep an eye on your fat intake. We will look at the correlation between fat and cancer risk in the next section.
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