E very paper and discussion of the metabolic theory of cancer begins with a description of what is referred to as the Warburg effect. As the bacterial colony grows, the available sugars are rapidly fermented. But in humans, fermentation by itself usually contributes relatively little to overall energy production. Yet as Warburg observed, cancer cells behave differently than normal cells: They become increasingly dependent on the fermentation of glucose within the cytoplasm of the cell for cellular energy. This differs from normal cells, which produce the majority of cellular energy within highly specialized organelles known as mitochondria.