I am interested in training in Brazilian Jiu Jitsu or Muay Thai, or even both. But I am inexperienced, having never trained in any martial arts whatsoever. I would like to get in shape before I join an Academy or any other place. Could anyone help me out and maybe give suggestions for a good: diet/cardio/weight lifting routine?

I already eat a lot of fruits and vegetables and lift weights occasionally. I heard drinking a lot of water was good and could actually help you lose weight. But I have heard other people say drinking lots of water makes you gain weight. Thanks for any suggestions.