Final answer:
Carbohydrate digestion starts in the mouth with salivary α-amylase, while protein digestion mainly begins in the stomach, and fat digestion predominantly takes place in the small intestine.
Step-by-step explanation:
Carbohydrate digestion begins in the mouth where salivary α-amylase initiates the breakdown of starch, a common carbohydrate, into smaller units such as dextrins, maltose, and glucose. The enzyme activity continues as food travels down the esophagus but ceases in the acidic environment of the stomach.
For the other macronutrients, protein digestion starts mainly in the stomach, whereas most fat digestion occurs in the small intestine with the aid of bile and digestive enzymes like lipases.