Given the limited scientific knowledge about dietary factors that affect cancer recurrence, dietary guidelines for cancer survivors are similar to general recommendations on healthy eating. This study explored the patterns of and motivation for, dietary changes among cancer patients. We conducted in-person interviews with 143 cancer survivors who were chosen from a mail survey on complementary and alternative medicine among cancer patients. We applied qualitative analysis using the software package NUD*IST to sort and code the transcribed interviews. The majority of dietary changes reported by 69 cancer patients agreed with current nutritional recommendations, such as decreasing meat and fat intake and increasing the consumption of vegetables and fruits. However, many diet changers also reported the intake of herbal and vitamin supplements, many with unproven effects. The major themes for changing diet were hopes that nutrition would increase well-being, maintain health and prevent cancer recurrence and beliefs that foods that cause or prevent cancer should be avoided and increased, respectively. Many cancer patients use non-scientific reasons when deciding on dietary changes and supplement use. Increasing communication with health care providers may prevent the use of extreme diets, unproven and possibly harmful supplements and reduce exaggerated hopes related to the benefits of a particular dietary regimen.