Which lipoprotein has the highest protein content?

• A. HDL
• B. LDL
• C. VLDL
• D. Chylomicrons

Answer: (A)

The key idea is that density of lipoproteins tracks with how much protein they contain relative to lipids. HDL has the highest protein-to-lipid ratio because it is rich in apolipoproteins (like ApoA-I), giving it the greatest protein content among circulating lipoproteins. This high protein content makes HDL the densest particle. In contrast, chylomicrons and VLDL carry lots of triglycerides and relatively little protein, so they are less dense, and LDL sits between HDL and the very triglyceride-rich particles. Hence, the lipoprotein with the highest protein content is HDL.