You don't. The energy you get in nuclear fission or nuclear fusion comes from the energy stored in the gluon or 'nuclear force' field which binds the quarks and nucleons together. There are no free lunches. It is true that the mass of a helium nucleus is LESS than the sum of the masses to two FREE protons and two FREE neutrons, but when they are combined into a helium nucleus, the difference in mass is locked up in the energy ( E = mc^2) of the nuclear force field. In fact, the proton (mass = 0.93148 GeV) consists of three quarks, but these three quarks have rest masses that are only about 15 MeV ( 0.015 GeV). The rest of the mass of the proton is stored in the gluonic field that binds the quarks together!