Agreed with the lion on this one also. Better part of the last 30 yrs. doing this, competitions, etc. and still do. Diet is key....I preach this all the time, use cardio as an "extension" of your diet, not the other way around. That is you are trying to create a caloric deficit with your diet, use your cardio as a tool to achieve this. First off, if you jump right into cardio, and do too much, you really have no place to turn but cutting more food calories. At some point this becomes unfeasible, and will most certainly backfire on you. Your body is smart, and will indeed learn to store fat...it will slow metabolic rate and thus thyroid output, hormones effected, as a defense mechanism. Our bodies are programmed fromn early days(being chased by predators, running through endless fields, etc.) to preserve life(by keeping an adequate fat store. The body does not care about looking good at the beach!
So use cardio as a tool to continue your caloric deficit, not the other way around.