First of all, understand that during a cancer treatment, a person should not eat anything that is not building the immune system or killing cancer cells.
For some kinds of cancer, meat eaters (especially red meat) have a higher probability of getting those kinds of cancer, such as colon cancer and prostate cancer. The reason for this is not entirely clear but may have something to do with too much animal fats or a lack of fiber.
Meat also uses up the two critical enzymes trypsin and chymotrypsin, which are theorized to be critical to allowing the immune system to kill cancer cells, though more potent enzymes have now been found. Vegetable proteins do not use up those enzymes.
Another reason to avoid meat is adherence to the theory that meat contributes to the accumulation of fecal matter in the colon. The colon should be relatively clear during a cancer treatment so that the body can absorb as many nutrients as possible. “All foods which ferment in the bowel should be avoided. Absolutely no meat or fish!” Additional concerns about meat consumption are theorized to be hormones, carcinogens (nitrosamines, nitrates, nitrites), and production of uric acid leading to a microbe friendly acidic environment. Patient testimonials regarding changes in diet leading to cancer remission are touted as evidence for avoiding meat altogether.
The Good News About Meat
According to the above theory, meat does have some nutrients that help prevent and deal with cancer and support the immune system. Meats have a low glycemic index, which is good. The problem is that meat overall does far more harm that good to your cancer treatment.
All in all, the bottom line of the plant based and raw foods diet is to avoid meats as much as possible, but that there are situations where a little meat (preferably poultry) can be beneficial, at certain times, in a cancer treatment.