For at least 100 years, doctors and self-proclaimed nutritionists have touted the idea that a particular diet can make cancer treatments work better. Some early clinical studies showed evidence of an effect. Now studies from top-class laboratories are leading to a new wave of experiments with more rigorous bases. Scientists are unraveling the molecular ways in which reducing calories or removing a food component can make tumors more susceptible to drugs. In mice with cancer, the effects are sometimes comparable to those of drugs given to patients. Still, convincing results from clinical trials will be required to overcome some oncologists’ view of special diets as fraying alternative medicine.