What substance has no energy (calorie) value but is essential for transporting nutrients in the body?

Water is essential for transporting nutrients in the body due to its role as a solvent and its ability to facilitate various physiological processes. Every cell in the body relies on water to maintain its shape and function, as it aids in the transportation of nutrients, hormones, and waste products. Water is involved in biochemical reactions and is critical for maintaining temperature regulation. Despite being vital for these processes, water has no caloric content, which means it does not provide energy in the form of calories like macronutrients do.

In contrast, other options such as salt, vitamins, and fiber do contribute to various bodily functions but can have calorie values or are not primarily involved in nutrient transport. Salt, while crucial for fluid balance and nerve transmission, is not specifically responsible for nutrient transport. Vitamins, although essential for numerous bodily functions, do not actively transport nutrients themselves. Fiber plays a role in digestion and can help regulate the absorption of nutrients, but it also does not provide energy. Thus, the correct answer highlights the unique role of water in the body as a nutrient transporter without adding caloric content.