MY CATS THROWING UP!! && i dont know why!?

My cat (Male, 3 years and 4 months) throws up his food, It's not watery or anything...Its still in the shape of his food! Just larger like it soaked up a lot of water...I'm not sure why...I don't remember when he's started doing this, but before we would feed him either Purina or IAMS, I think maybe both, now he eats Meow Mix, my other cat eats the same food but I've never seen her throw up. They've never had hair either. Could It just be the food? He's very active and is always chasing the other cat around the house, playing with us, sleeping around and being lazy like usually...We rarely ever feed them human food but I've never found any in their food. Also, afterwards he eats it up again if we don't clean it up in time. I only see him do it about once or twice a month maybe, but since me and my brother are at school and my moms at work till 6 we wouldnt know if he does it during the day. Any other details I can add I will try, Your info will be gladly appreciated! Thanks!