BACKGROUND & AIMS: It is widely acknowledged that the energy metabolism of cancer cells mainly relies on anaerobic glycolysis and this has prompted many researchers to try to reduce the malignant cells growth of experimental tumours through a programme of calorie restriction. Recently this approach has been proposed also to cancer patients. In the meantime it was demonstrated that the effects of calorie restriction on tumour growth are mediated through the toxic effect of ketone bodies on cancer cells which have a defective mitochondrial function, while these substrates are well-utilized by the normal cells. METHODS: This review analyzes the main available data regarding the tumour growth in patients undergoing a period of starvation or of normal/artificial nutrition as well as the recent approach through special normocaloric ketogenic diets which are well utilized by cancer patients while may be unfavourable for cancer cells. RESULTS: Despite the paucity of data it appears that modulation of tumour growth by the calorie restriction/nutritional support is unlikekly in humans for several reasons: the different tumour cells growth rate and different tumour/host carcass ratio and duration of treatment, between tumour-bearing animals and patients. CONCLUSION: There is a large consensus in literature that maintaining a normal body weight and preserving the lean body mass through an adequate nutrition is beneficial in cancer patients. The nutritional approach through a ketogenic diet which may be toxic for the cancer cells while is well utilized and tolerated by the patient seems promising in a next future.