My son is 15.5 yrs of age, length 1.80 m and weighs 52 kg. He is very active, runs x-country and swims a lot, but his food intake is minimal. He s just had a physical and was pronounced healthy, but underweight. If he has had a major competition, he needs a day or two to recover afterwards and is prone to headaches. He gained just 2 kg in the whole of 2016, so am considering putting him on an appetite enhancing drug. I d rather not, but we have been battling this issue for so long now and I m worried he s causing damage to his body.