Which nutrient is typically the body's primary energy source?

• A. Carbohydrates
• B. Fats
• C. Proteins
• D. Vitamins

Answer: (A)

Carbohydrates are typically the body's primary energy source because they can be quickly converted into glucose, the fast fuel used by both muscles and the brain. When you perform work, glucose is rapidly broken down through glycolysis to produce ATP, the molecule that powers contractions. The body also stores glucose as glycogen in the liver and muscles for quick access during activity.

Fats provide a large amount of energy per gram, but their breakdown is slower and requires more oxygen, so they mainly fuel longer, lower-intensity efforts. Proteins aren’t a primary energy source; they are primarily used for tissue repair and enzymes, and vitamins don’t supply calories but help energy metabolism. So carbohydrates are the body's main energy source.