What is the primary source of energy for the body's cells?

The primary source of energy for the body’s cells is glucose. Glucose, a simple sugar, is pivotal in cellular respiration, a process that allows cells to extract energy from nutrients. When carbohydrates are consumed, they are broken down into glucose, which is then transported through the bloodstream to various cells, where it undergoes glycolysis and further metabolic pathways to produce adenosine triphosphate (ATP), the energy currency of the cell. This efficient conversion of glucose into energy is fundamental for cellular functions, especially in tissues such as the brain and muscles, which rely heavily on glucose for their energy needs.

Other macronutrients, while they can also provide energy, do so in less direct ways or are used more slowly. Proteins serve primarily for structural purposes and as enzymes rather than as energy sources. Starch, being a complex carbohydrate, must first be broken down into glucose units before it can be used for energy. Lipids provide energy as well but are primarily stored and used during prolonged activity or when carbohydrate sources are low.