When an individual is in an energy deficit, where is the remaining energy required for normal physiological function and exercise obtained from first?

When an individual is in an energy deficit, the body primarily relies on adipose tissue to obtain the energy required for normal physiological functions and exercise. Adipose tissue serves as the body's main storage form of excess energy, primarily in the form of triglycerides. During periods of inadequate caloric intake, the body mobilizes fat stores through a process called lipolysis, breaking down stored triglycerides into free fatty acids and glycerol, which can then be used as fuel for energy.

The use of adipose tissue as the first source of energy during an energy deficit is also critical for preserving muscle mass. If the body were to rely excessively on skeletal muscle or protein stores, it would lead to muscle wasting and impair overall metabolic function. Carbohydrate stores, while important for immediate energy needs, are generally lower in capacity compared to fat stores and are also depleted more quickly.

This makes adipose tissue the most efficient and primary source for energy during states of energy deficiency, enabling the body to maintain essential functions while minimizing the loss of lean muscle mass.