Hydrogen of course, because water is the most abundant in our body, nearly 42% of 75 kg human body is made up of water,i mean H2O,so hydrogen is the answer
But each and every protein,fat and carbohydrate contain carbon skeleton...do if water is 42% ....then evry structure of our body has protein,fat and carbohydrate....so accordingly it should have more of carbon!!
Its not carbon... Carbohydtate contain H and O,and protein made up of AA' contain carboxyl group again H and O...fat is also contain H and O....but in H2O no carbon....