Final answer:
A purified diet is used in nutritional studies for precise knowledge of dietary components, including specific nutrient amounts required for a balanced diet depending on individual requirements.
Step-by-step explanation:
The type of diet often used in nutritional studies that require a precise knowledge of diet components is C) Purified diet.
A purified diet consists of well-defined ingredients that allow researchers to know the exact quantities of nutrients and the caloric content being consumed. Unlike diets composed of complex food items like pellets, crumbles, or hay-based diets, purified diets are meticulously formulated to ensure that all the components of a balanced diet are included in specific amounts, catering to the requirements based on age, sex, physiological needs, and physical activity levels of the study subjects.
This enables the precise control and repeatability necessary in experimental designs to assess the health effects of individual nutrients or diet composition.