Nutrition & Cancer:
What is the Connection?
Does what we eat really affect our risk
The National Cancer Institute estimates that at least 35% of all cancers have a nutritional connection. When lifestyle factors such as smoking and exercise are included the associated risk becomes much stronger and may be as high as 85%. What we eat makes a big difference in our energy levels, our mood and even our self esteem. When we choose foods rich in protective factors such as fruits and vegetables we are also doing something positive for our health and well-being.
Which foods are important for health?
Foods that come from the plant kingdom rather than the animal kingdom have many protective botanical factors: plants cannot move away from danger, unlike animals. These phyto (meaning plant) nutrients can be beneficial to us also. Antioxidants, anticarcinogens and bioflavonoids are some of the terms used to describe the actions of phytonutrients. Foods rich in botanical factors or phytonutrients include berries, dark green leafy vegetables, citrus fruits, legumes (beans of all sorts including soy) and whole grains.
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If we emphasize those that are supportive to our health then we will find ourselves eating less of the foods that contain "empty" nutrients. These foods may provide pleasure so we need to keep them in our diet at low levels only. Such foods include desserts, cakes, candies and many items made with saturated animal fats. I prefer to think of the 80:20 rule when selecting foods. 80% of the time we should choose healthful foods from the plant kingdom such as those listed above, and 20% of the time we can choose foods that provide pleasure and may not be quite as healthful.
Studies are ongoing in many centers looking at the benefits of soy protein in those at risk of breast and prostate cancer. Soy protein contains several active phytonutrients that may protect against hormone sensitive cancers partly by blocking receptors with plant estrogens called genistein and daidzein and partly by the action of the Bowman Birk inhibitor or other protease inhibitors naturally present in the beans. Lecithin is also an important component of soy foods.
Frying or charbroiling meat or fish may cause carcinogens on the surface by the action of the heat. Smoking or nitrite curing meats may also form carcinogens. These carcinogens may not be harmful when consumed in small quantities and particularly when we eat them with fruits and vegetables that contain protective botanical factors. It is wise to use lower heat methods for most of our cooking methods such as steaming, braising, poaching, stewing or microwaving. Marinades help to make cooked meats safer.
Can eating fish be protective?
Oily fish such as salmon, herring, mackerel, halibut and tuna contain oils rich in omega-3 fatty acids. Docohexanoic acid (DHA) and Eicosopentanoic acid (EPA) are two of these long chain polyunsaturated fatty acids that occur in fish and in certain vegetables. These are protective in animal studies. It is recommended that you try to eat foods rich in omega-3 fatty acids several times each week. Fish is a good source but berries, mushrooms and Brussels sprouts are also dietary sources of omega-3 fatty acids.
Why is dietary fiber important in cancer prevention?
Dietary fiber is the indigestible part of foods of plant origin (it doesn't occur in any foods that come from animals, e.g. butter, meat, eggs, fish). Fiber provides bulk to our diet and helps to maintain a healthy colon. It does this in several ways; first, it stimulates muscle contractions and hence reduces colon transit time (minimizes constipation). Secondly, it dilutes any potentially hazardous or carcinogenic substances and also reduces the amount of time these substances would be in contact with the colon wall. Thirdly, it provides an environment that is conducive to "friendly" bacteria or acidophilus. These are supportive to us as they partially digest some of the fiber and provide us with nutrients and they also maintain a healthy acidic level in the colon. All of these factors are synergistic and hence eating dietary fiber throughout the day provides the best environment in our colon that is reflected in our overall health. Cholesterol and steroid hormones that are similarly structured including the sex hormones, estrogen and testosterone as well as vitamin D and cortisol are regulated in part by secretion into the digestive tract via the bile and reabsorption. Dietary fiber plays an indirect part in regulating the reabsorption as the bacteria acts on some of these bile acids and assists in their excretion.
Most Americans eat about 10 grams of dietary fiber each day but this is about half of what is ideal. The suggested range is 25-35 grams spread over the day. This is best accomplished by eating fiber rich foods at each meal such as whole grain cereals, breads, pastas, beans, leafy vegetables, fruits, nuts and seeds.