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MORE ON DIET, EXERCISE, AND CANCER PREVENTION
(December 2003)

The scientific and health journals, newspapers, radio, television, and internet are filled with reports that purport to offer specific ways you can reduce the risk of cancer by dietary change or manipulation or by taking a variety of dietary supplements. Most of the recommendations represent: new and, as yet, unconfirmed findings; undocumented claims; exaggeration; and, in some cases, pure malarkey.

The following is what we can recommend with reasonable confidence based on the available evidence.

1. Avoid overweight. There are two components to this. The first is to avoid being more than 20 percent overweight (the measurement used most now is the Body Mass Index - BMI - weight in kilograms divided by the square of the height in meters. CLICK HERE for a chart that will give you your BMI. You can also use height-weight tables - CLICK HERE for those tables).

Once you are 20 percent overweight (BMI 30 or over), the risk increases for cancers of the body of the uterus, ovary, gallbladder, breast (post-menopausal women only), kidneys, and maybe the bowel. For many of these, the risk is particularly increased for those who are 40 percent or more overweight.

The second component relates to the distribution of the excess weight. In general, health risks are greater when overweight is concentrated in the abdomen. That appears to be true for breast cancer; it has not been adequately studied for other cancers. The definition of abdominal overweight needs more study, but individuals can tell when they have protruding abdomens. One definition is a waist circumference for men of more than 40 inches and for women of more than 35 inches. That may not be accurate for some people, and may over diagnose obesity. Another measurement, maybe better, is a ratio of more than 1 for waist:hip circumference.

2. Exercise regularly. The protective role of exercise is pretty well established for bowel and breast cancers. What is not settled is how much total exercise is needed and how intensive (vigorous) it needs to be. Physical activity is now measured in METs. A MET is the energy expended (calories burned, oxygen used) at rest. Two METs is twice resting energy expenditure. Slow walking is 2 METs per hour intensity. Walking briskly (3 miles an hour, one mile every 20 minutes) is 3.5 METs per hour intensity and is moderately vigorous. The evidence suggests that regular moderately vigorous or vigorous physical activity is needed to offer moderate protection against bowel cancer. Although the evidence is not clear, the same is recommended for breast cancer prevention. Healthful Life recommends at least 12 MET hours a week of at least moderately vigorous physical activity as a minimum; 20 MET hours a week is an even better idea. For example, walking at a pace of 3 miles an hour for one hour four times a week would be 14 MET-hours.
(CLICK HERE for a table of intensity in METs of various activities. Weekly MET-hours is determined by multiplying the MET intensity of each activity by total hours of that activity each week, and then adding all the activities together to get the total MET hours for the week.)

But, realize we do not have definitive evidence on the total amount of and intensity of physical activity, so all we can give you is what appears to us to be a sensible recommendation. If you cannot do moderately vigorous activity, try to reach a total of 12 MET-hours a week (for example, by walking at an average pace for five hours a week). If you cannot do that much, at least try to avoid being sedentary.

3. Eat plenty of vegetables and fruits - at least four servings a day (some would recommend 6, or even 8, servings a day). Cruciferous vegetables (such as cauliflower, cabbage, broccoli, brussel sprouts) appear particularly beneficial. Vegetables and fruits taken together as a group appear to reduce risk of several cancers, including esophagus, stomach, probably bowel, and perhaps breast - and maybe others. (The evidence on breast cancer is unclear.)

4. Get enough calcium in your diet or by supplements. A good calcium intake may reduce the risk of bowel cancer. An adequate calcium intake (at least 1,000 milligrams a day for a man, 1,200 milligrams for a woman) is needed to build and maintain strong bones. If it also reduces risk of bowel cancer (a reasonably good possibility), so much the better.

5. Make sure your folic acid intake is adequate. Everybody should get at last 400 micrograms (preferably at least 800 micrograms) in the diet or through supplements. That is the best way to keep homocysteine levels in a desirable range (homocysteine is a risk factor for coronary heart disease and heart attacks). Folic acid may also protect against heart attack by other mechanisms. Although it is not fully proved, there is a reasonable amount of evidence indicating that folic acid can offer moderate protection from bowel cancer, at least in some people. A good folic acid intake is mandatory for every women who might get pregnant to prevent certain potentially serious neurologic abnormalities in the baby.

That is it. There are still uncertainties, such as the amount or intensity of physical activity, but that is what we can recommend with reasonable confidence in regard to an anti-cancer diet and exercise program. That is what everyone should be following.