A chemical in carrots called falcarinol was found to increase proliferation of colon cancer cells in low doses. However, if you ingest high doses of carrots you can strongly induce programmed cell death (apoptosis) in these same cells. While this study was done on rats, it could explain claims from those using Gerson therapy to treat various cancers such as colon cancer. In Gerson therapy they rely heavily on large amounts of fresh juices and carrot juice is one of the major constituents. This suggests that if you have colon cancer, having a few carrots a day might be a bad idea. Juicing carrots, however, will provide the high doses necessary to kill colon cancer. You should, however, juice in the appropriate dose. Specifically, the falcarinol should be greater than 10 microM. For more information, or if you are interested in a consultation, our oncology support is headed by Steve Gomberg.
 
J Agric Food Chem. 2007 Feb 7;55(3):618-23