There is significant use of alternative diets by people living with cancer, with data suggesting this has continued to increase since the 1980s. Commonly used alternative diets include the ketogenic diet, Gerson therapy, alkaline diets and fasting diets. This article explains the latest trends in relation to alternative diets, discusses the reasons why people may want to use these and examines their hypothesised mechanisms of action. The author outlines and critically reviews the evidence underpinning the use of such diets in those living with cancer, and suggests that this remains weak. The article also explores the challenges that nurses may experience when a person living with cancer wishes to adopt an alternative diet, and provides practical advice and recommendations on nutrition.