  We present a whole-body model of human metabolism that utilizes a system of
organs and blood vessels to simulate the enzymatic reactions. The model focuses
on key organs, including the brain, heart and lungs, liver, gut, and kidney, as
well as muscle and adipose tissue. The model equations are formulated using
stoichiometry and Michaelis-Menten kinetics to describe the enzymatic
reactions. We demonstrate how the model can be used to simulate the effects of
prolonged fasting and intermittent fasting on selected metabolite
concentrations and glucose flux. Furthermore, by simulating intermittent
fasting the effect on the carbohydrate, the protein and the lipid storage is
examined. We propose this method as a simple and intuitive approach for
modeling the human metabolism, which is general, systematic and easy to
incorporate. This could have potential applications in PK/PD drug development
and in understanding metabolic disorders.
