The human body contains many salts, of which sodium chloride NaCl is the major one, making up around 0.4 per cent of the body's weight. So a 50kg person would contain around 200g of sodium chloride - around 40 teaspoons. Since we lose salt whenever we sweat, it has to be continually replaced.
Answer: 0.4% of body weight.
//Not sure, but hope it helps.