Which of the following is NOT a type of carbohydrate?

Carbohydrates are one of the primary macronutrients and include substances that provide energy, such as starch, sugar, and fiber. Starch is a complex carbohydrate that serves as a significant energy source, primarily found in plants. Sugar represents simple carbohydrates, which are quickly absorbed by the body and used for energy. Fiber, although not digestible by the human body, is essential for digestive health and is derived from plant foods.

Proteins, on the other hand, are made up of amino acids and serve different functions in the body, including building and repairing tissues, making enzymes, and supporting immune function. They are not classified as carbohydrates but are rather one of the other main macronutrient groups. Thus, identifying protein as not being a type of carbohydrate accurately reflects the nutritional classification of these macronutrients.