What is one role of lipids in nutrition?

• A. They provide a concentrated source of energy
• B. They are the primary nutrient for hydration
• C. They are the main source of oxygen in the blood
• D. They fix nitrogen in tissues

Answer: (A)

Lipids provide a concentrated source of energy because they yield about 9 kcal per gram, more than carbohydrates or proteins. This high energy density makes fats a crucial long-term energy reserve and especially important during prolonged, lower-intensity activity when fat oxidation becomes a major fuel. Hydration comes from water, not fat; oxygen in the blood is carried by hemoglobin in red blood cells; nitrogen fixation is performed by certain bacteria, not by lipids. Lipids also play roles in absorption of fat-soluble vitamins and supplying essential fatty acids, but the key point here is their energy density.