The process of consuming energy depends on glucose. Ultimately, proteins, lipids, and carbohydrates all decompose into glucose, which is subsequently used as the main metabolic fuel for animals and the foetus. The production of several carbohydrates, including glycogen, ribose and deoxyribose, galactose, glycolipids, glycoproteins, and proteoglycans, uses it as a significant precursor. In contrast, plants use photosynthesis to create glucose from carbon dioxide and water, which is then stored as starch. Most frequently, at the cellular level, glucose is the last substrate to enter tissue cells and convert to ATP (adenosine triphosphate).

The body uses ATP as its primary form of energy for a variety of processes, including the active transport of molecules across cell membranes, muscle contraction and mechanical work, synthetic reactions that produce hormones, cell membranes, and other essential molecules, the transmission of nerve impulses, cell division and growth, and other physiological processes.

Under feeding circumstances, the digestive tract's numerous glucosidases break down and process dietary carbohydrates, producing monosaccharides, mostly hexose glucose, which are then carried into various tissues where they serve as the main fuel for ATP synthesis. The process of breaking down glucose into pyruvate, known as glycolysis, is still a significant mechanism for producing ATP in the majority of mammalian tissues. Cytosolic pyruvate is carried into the mitochondrial matrix in tissues with an abundance of mitochondria, where it is transformed to acetyl-CoA by the pyruvate dehydrogenase complex and then combined with oxaloacetate to form the tricarboxylic acid cycle. Both NADH and FADH2, which are crucial electron carriers for the electron transport chain-oxidative phosphorylation that produces ATP, are produced by the cycle together with energy equivalent to ATP (i.e., GTP).

Pyruvate is occasionally transformed into lactate in the cytosol to replenish the NAD+ required for the ongoing production of ATP through substrate-level phosphorylation via anaerobic glycolysis, such as in red blood cells missing mitochondria or cells experiencing ischemia. Glycogenesis is the process through which extra carbohydrates in the liver are first transformed into glycogen, an animal storage form of glucose. Additionally, in a diet high in carbohydrates, the excess carbohydrates are converted into fatty acids by a process known as lipogenesis using the acetyl-CoA produced by the glycolysis of pyruvate. These fatty acids are then transported to white adipose tissue for storage by very low density lipoproteins.

The preservation of constant blood glucose levels is known as glucose regulation. The pancreas secretes hormones that control how glucose is metabolised throughout the body. The main hormones responsible for keeping blood glucose levels stable are insulin and glucagon, and the amount of foods determines how much of each is released. The amount of glucose that cells break down depends on both the amount of insulin released in the circulation and the sensitivity of the cells to the insulin. The enzymes that catalyse glycogenolysis are activated by a rise in glucagon levels, while the enzymes that catalyse glycogenesis are inhibited. In contrast, when blood insulin levels are high, glycogenolysis is blocked and glycogenesis is boosted.