Energisubstrat

Energisubstrat, or energy substrate, is a molecule that can be oxidized to generate energy in the form of adenosine triphosphate (ATP) to power cellular processes. In metabolism, substrates are consumed by pathways that extract chemical energy, typically through glycolysis, beta-oxidation, the citric acid cycle, and oxidative phosphorylation. The availability and use of energy substrates determine how cells meet their energetic demands and adapt to different physiological states.

Common energy substrates include carbohydrates (primarily glucose and glycogen), fats (free fatty acids and triglycerides), and certain amino acids that can be converted into intermediates for energy production. Under fed conditions glucose predominates; during fasting or prolonged exercise, fats and ketone bodies become major substrates. Lactate can also serve as a substrate in tissues that perform the Cori cycle or in the heart and brain under stress.

Energy yield varies by substrate and pathway. Complete oxidation of one glucose molecule yields about 30 to 32 ATP in most tissues. Fatty acids provide a high energy yield per molecule; for example palmitate oxidation yields many tens of ATP. Energy yield per gram is higher for fats (about 9 kcal/g) than for carbohydrates or protein (about 4 kcal/g). The relative use of substrates is reflected by the respiratory quotient and is influenced by hormones and energy balance.

Measurement and research: Indirect calorimetry estimates substrate use by comparing oxygen consumption and carbon dioxide production. Stable isotope tracers allow tracking of specific substrates, while metabolic models integrate data on nutrient intake, hormonal status, and energetic needs to understand substrate allocation.