The mass of every person can be calculated by adding up the mass of all the protons and neutrons from each atom in us. HOWEVER…protons and neutrons are made up of quarks and when you add up the mass of the quarks they are only about 2% the mass of an atom. Quarks move at incredible speeds inside a very small area in a proton and neutron so they store a great deal of potential energy and because of the equivalence of energy and mass that is where the extra mass is located.

(The Great Courses – The Theory of Everything: The Quest to Explain All Reality)