For weight maintenance, the energy in must equal what?

For weight maintenance, the principle of energy balance is crucial, meaning that the energy consumed through food and beverages must equal the energy expended through various activities and metabolic processes. When energy in equals energy out, the individual's weight remains stable, as there is neither a surplus (which would lead to weight gain) nor a deficit (which would lead to weight loss). This equilibrium allows the body to maintain its current mass and ensures that all its systems function optimally without requiring structural changes in body composition. As such, the statement that energy in must equal energy out is fundamental to understanding how to achieve and sustain weight maintenance effectively.