The main source of energy in the human diet is d. carbohydrates.
Carbohydrates are the body’s primary energy source. They are broken down into glucose, which is used by the body’s cells for energy. Foods rich in carbohydrates include bread, rice, pasta, fruits, and vegetables. While fats and proteins also provide energy, carbohydrates are the most efficient and readily available source.
Fats are a secondary energy source and are used when carbohydrate stores are low. Proteins are primarily used for building and repairing tissues, although they can also provide energy. Steroids and nucleotides are not significant sources of energy in the human diet.