Which of the following is essential for building muscle and blood tissues and for repairing and replacing cells?

• A. Carbohydrates
• B. Vitamins
• C. Lipids
• D. Proteins

Answer: (C)

Proteins serve as the building blocks for body tissues. Amino acids, the components of proteins, are assembled to form the structural and functional proteins that make up muscles, blood components, enzymes, and connective tissue. In muscles, proteins like actin and myosin enable growth and contraction; in blood, proteins such as hemoglobin carry oxygen and plasma proteins help regulate fluid balance and transport substances. When tissues need to be repaired or replaced, the body relies on protein synthesis to rebuild cells, making adequate dietary protein crucial for recovery after injury and for ongoing growth.

Lipids provide energy and form cell membranes but do not supply the primary building blocks for new tissue. Carbohydrates mainly fuel activities, and vitamins act as cofactors that support metabolic processes rather than serving as the direct structural components of tissues.