Cancer develops as a result of irregular functioning of the regulatory mechanisms of the cell. Because tumour cells do not respond to growth control signals, they divide rapidly and spread to normal tissues. Diet and physical activity have a significant impact on the formation and development of such cells. Their main source of energy is glucose which they metabolize by aerobic glycolysis (Warbug effect) in much larger amount than normal cells do. In addition to glucose, the growth and development of tumour cells are also affected by the levels of insulin, insulin-like growth factor (IGF-1) and leptin, all of which can be regulated by diet. That is why the effect of fasting and certain diets on the prevention and treatment of cancer is being studied. Such dietary protocols promote autophagy in healthy cells which protects them from the toxic effects of chemotherapy while making tumour cells more sensitive to it. They also greatly reduce the side effects of such treatment. In addition to diet, the effect of certain nutrients is also being studied, and depending on the required levels, their supplementation or restriction in the diet is applied.