Building muscle mass and definition is hard work and requires the proper diet to make it happen. When building muscle, it is necessary to eat a variety of nutrient-dense foods with the right blend of proteins, carbohydrates, and healthy fats.
When trying to build muscle, people often make the mistake of restricting caloric intake from a particular type of nutrient or restricting total calories. But muscle is the fuel your body will turn to when your calories are low. When you don't eat enough to sustain muscle growth, your body will go into starvation mode and increase rather than decrease fat stores.
If you are exercising to build muscle, there is no need to simultaneously restrict calories to lose weight. Maintain a balanced diet of requisite proteins, carbs, and fats, and your body composition will improve over time.