What is the primary role of carbohydrates in the diet?

The primary role of carbohydrates in the diet is to provide energy. Carbohydrates are the body's main source of fuel, particularly for the brain and during physical activity. When consumed, carbohydrates are broken down into glucose, which is then utilized by the body’s cells to generate energy. This energy is essential for all bodily functions, including muscle contraction, organ function, and metabolic processes. Moreover, carbohydrates can also be converted to glycogen, which is stored in the liver and muscles for later use during periods of low energy intake or increased physical demand.

While the other options mention important aspects of nutrition, they do not represent the primary function of carbohydrates. Vitamins are supplied primarily by fruits, vegetables, and whole grains, while muscle building is mainly supported by proteins. Improving digestion is largely influenced by dietary fiber, which is one of the types of carbohydrates, but it is not the primary role of carbohydrates as a whole. Thus, the predominant function of carbohydrates remains energy provision, making it the correct answer.