Final answer:
Sugar is not considered a nutrient because, although it provides energy, it lacks essential dietary elements needed for the body's growth and maintenance.
Step-by-step explanation:
The student's question asks which option is not a nutrient. Out of the choices given: Protein, Water, Fats, and Sugar, the one that is not categorized as a nutrient is Sugar. Nutrients are substances that provide nourishment essential for the maintenance of life and for growth.
Proteins, fats, and water are all essential nutrients that the body needs to function properly. Proteins and fats provide energy and are involved in numerous metabolic processes, while water plays a critical role in maintaining the health of every cell in the body.
Sugar, while it provides energy, is not considered a nutrient because it does not contain essential dietary elements necessary for the body's growth and maintenance. Therefore, the correct answer is D. Sugar.