DS is 15. Eats relatively healthily for a bit of his age. Loves fruit and vegetables, doesn't like sweets but is partially to chocolate cakes, bolognese and anything and everything else really.
He is over weight for his height, has man boobs (quite distinct) and for as long as I can remember he has had loose bowels and has been a2/3 times a day man, always with explosions rather than what I believe are healthy looking stools.
Any ideas as to what his diet might be missing? He's okay at taking tablets so I can give him any number of supplements. He was taking fish oils but suddenly he has decided that they taste vile. 
TIA