Feature Articles - Aging
Which Foods to Avoid for a Colon Cancer Test
Susan Mills-Gray, Nutrition Specialist, Cass County Extension Center, University of Missouri Extension
Your doctor gives you a little kit to collect tiny samples of fecal matter that will be mailed to a lab and checked for hidden blood - a possible sign of colon cancer. The box says to avoid certain foods and medications. But the doctor tells you to ignore the restrictions. Now you're really confused and may just decide to chuck the whole thing.
It's understandable. After all, taking the test is difficult enough. The confusion over dietary restrictions only adds to the unpleasantness - which may help explain why the majority of people 50 and older don't take the test once a year, even though they're supposed to. Colon cancer, second leading cause of cancer death in the US after lung cancer, is most likely to affect people over 50. The 5-year survival rate for colon cancer caught early is over 90%. Only about one-third of all colon cancer cases are found in an early enough stage to contain them, in large part of poor participation in screening practices.
Part of the reason sources don't agree on which foods to avoid during the fecal occult blood test is that different brands of tests use different chemicals and different laboratory methods to check for blood. That could change the dietary requirement to some degree The truth is that we just don't have all the science to know which foods would be more likely to affect the test results and which wouldn't. A false negative is much worse than a false positive, but both impact the quality of life.
Here's what we know as of today: red meat contains blood that can be mistaken for human blood, creating a false positive result. Aspirin and other nonsterodial anti-inflammatory drugs (NSAIDs) can also create false positives by causing GI bleeding that has nothing to do with abnormalities in the colon. So can iron supplements, because of the way they interact with the chemicals on the test card. Vitamin C supplements in amounts above 250 milligrams can interfere with the chemistry of the test, too, creating a false negative. But it's not known just how much of these substances can lead to faulty results, or under what circumstances.
If you're going to bother to take the test, you might as well do it with as many safeguards for accuracy as possible. That means foregoing red meat, iron and vitamin C supplements, NSAIDs, and the following vegetables and fruits: broccoli, cauliflower, radishes (including horseradish sauce), turnips, and cantaloupe, during the 3 days of testing as well as the 3 days before. Also note that certain toilet bowl cleaners can trigger false negatives, too. Don't use toilet bowl cleaner on or in the bowl for several days before and during the testing days.
Last update: Tuesday, May 05, 2009