In the case of nuclear fission, when U-235 splits into Ba,Kr and three neutrons , then it is shown that the total mass of the products on the right side of the equation is slightly less than that of the reactants on the left side. So this missing mass-the mass defect – is converted into energy and released. But in the case of a nuclear fusion reaction, when 4 hydrogen nuclei fuse together and form a helium nuclei there also energy is released ie.27.6 MeV per fusion. But how this mechanism can be explained? Because in this reaction the total energy on the left side is calculated as 4.4 MeV and that of the product nuclei ie. He, is given as 28 MeV. Here the energy on the right hand side is found greater than that of the left side. Logically in this reaction it appears as if the energy is only absorbed, but not released. Then how we do we get the energy released in the fusion reactions as in the case of fission reactions? Can anybody kindly explain this contradiction in a simple manner?