Specific Dynamic Action (SDA), also called the Heat Increment of Feeding (HIF) or Diet-Induced Thermogenesis, refers to the mandatory postprandial increase in metabolic rate and energy expenditure above basal levels associated with the mechanical ingestion, digestion, absorption, and biochemical assimilation/deamination of dietary nutrients (especially proteins).

In mitochondrial $\beta$-oxidation of saturated even-numbered fatty acyl-CoA chains, each repetitive four-step cyclic cleavage sequentially releases a 2-carbon fragment in the form of Acetyl-CoA ($CH_3-CO-SCoA$), which directly enters the Krebs citric acid cycle for ATP generation.

In nutritional bioenergetics, dietary energy partitions through progressive losses:

$$\text{Gross Energy (GE)} \xrightarrow{-\text{Fecal loss}} \text{Digestible Energy (DE)} \xrightarrow{-\text{(Urinary + Gill branchial loss)}} \text{Metabolizable Energy (ME)}$$

Because energy is lost in nitrogenous urinary and branchial excretions, Digestible Energy is strictly greater than Metabolizable Energy ($\text{DE} \gt \text{ME}$).