Every real transformation produces entropy and ultimately degrades some capacity to perform useful work.
The precise statement is:
Energy is conserved; usable free energy is progressively degraded.
Operational definition
Energy output.
Thermal energy transferred from the biological system to its surroundings as a result of metabolic reactions, molecular friction, transport, mechanical work, and other irreversible transformations.
Heat is not destroyed energy. It is energy dispersed into a form with less capacity to perform organized biological work under ambient conditions. Ecological production accounting separates retained biomass and reserves from exports, waste, respiration, and heat; biological transformations conserve total energy while degrading available free energy. (OpenStax)