Fig 1. Model structure of compartmental model.

The same structural model was used for all individuals and in both the mixed effects and the STS model. Model constraints, k _2,1 = k _1,2, k _3,4 = 0.1 k _4,3, k _9,8 = k _7,5 and k _0,9 = k _0,7 were used. Compartment 1 represents the free leucine in the plasma, compartments 3 and 4 represents leucine recycling in non-hepatic tissue and compartment 2 is the intrahepatic leucine that feeds the apoB synthesis compartment represented as a delay (D₁-D₇). Newly synthesized apoB enters the plasma as VLDL₁ (large particles, compartment 5) or VLDL₂ (small particles, compartment 8). VLDL₂ may also be produced through conversion of VLDL₁ via compartment 6. Particles may leave the system through compartments 6, 7, 9 or 10.