resistance training

Not necessarily, because the types of mass you are gaining/losing are totally different. Cardio burns fat, while lifting builds lean muscle.

Granted, the diets that go along with each type of training are slightly counter productive. But that doesn’t mean that your body will stay in a stailmate if you try to do both at the same time.

For example, when you lift to gain mass, you are usually supposed to eat plenty of calories, including extra carbs and protein for your muscles to use as energy to work and build themselves. This diet would slow down (but not stop) the effects of cardio training, but you would still see yourself becoming leaner, asssuming that your cardio training was intense enough.

Likewise, if you eat as if you’re trying to lose pounds fast, your body will not have enough nutrients to properly repair itself quickly, thus making the muscle building process take longer than it would have to.

I say eat a normal, healthy diet, and rotate every few days between cardio and resistance training. This way you will see both results at the same time.