Which of the following best defines a lipid in the context of nutrition?

• A. Any dietary molecule that provides 4 kcal per gram and is primarily used for immediate ATP production in cells rather than structural roles, which distinguishes it from lipids and proteins.
• B. A group of water-soluble biomolecules composed primarily of repeating sugar units and polar functional groups that readily dissolve and form hydrogen bonds in aqueous environments.
• C. A category of polymers made up of amino acids linked by peptide bonds that form structural and enzymatic proteins and rarely includes hydrophobic regions used for membrane interactions.
• D. A class of organic molecules largely insoluble in water that includes fats, oils, phospholipids, and sterols.

Answer: (D)