In their natural state within the body, cells normally depend on cellular respiration as the source of energy and ATP. During times of complete or partial food deprivation these cells can also rely on ketosis as an additional energy source. Tumor cells in contrast are defective in this respect, lacking in the ability to utilize ketone bodies for energy and instead are heavily dependent on glycolysis for their survival. Malignant cells depend heavily on glycolysis for energy production even in high oxygen states. If the investigators limit the supply of glucose, glycolysis would decrease and tumor cells would lose their main source of energy supply.