What is best defined as a nutrient that cannot be synthesized by the body?

An essential nutrient is defined as a nutrient that the body cannot synthesize on its own and must be obtained through diet. Essential nutrients play vital roles in numerous bodily functions, including growth, metabolism, and overall health. They include certain amino acids, fatty acids, vitamins, and minerals that are crucial for the body to function correctly.

While minerals and vitamins are specific categories of essential nutrients, the term "essential nutrient" encompasses a broader range of substances needed for optimal health that cannot be produced by the body. For example, some fatty acids and amino acids are classified as essential because the body requires them but cannot create them from other molecules. This is why they must come from food sources.

Macromolecules, on the other hand, refer to large complex molecules like carbohydrates, proteins, and nucleic acids and are not defined by their necessity for the body in the same way essential nutrients are. Hence, the classification of what constitutes an essential nutrient is critical to understanding nutrition and health.