Which nutrient is primarily responsible for energy during physical activity?

The nutrient primarily responsible for energy during physical activity is carbohydrates. Carbohydrates are the body's main source of fuel, especially during intense exercise. When consumed, carbohydrates are broken down into glucose, which is then utilized by the muscles and brain for energy. This process is essential for endurance and performance, as carbohydrates provide quick energy that helps sustain activity levels during physical exertion.

While protein does play a role in muscle repair and growth, its primary function is not to supply immediate energy during physical activity. Instead, the body typically turns to carbohydrates for that purpose. Vitamins are essential for numerous metabolic processes and overall health, but they do not provide energy directly. Fiber, while important for digestive health, does not provide energy in the same way carbohydrates do; instead, it aids in digestion and helps maintain stable blood sugar levels. Thus, carbohydrates are the dominant nutrient for energy use during physical activities.