Just a guess, but they (the ryugakusei) met lots of full-blooded Keio students whose parents and/or grand parents were Keio graduates and their kids went to Keio from its kindergarten.
Tell him to summon onigiri rice balls, not bread, in breakfast for his first three months, (if possible not to use a fry-pan dishes, either), and I am 100% sure that he will lose weight.