Whether you are looking to gain weight or increase muscle mass, training alone is not going to cut it for you! Did you know that in order to increase muscle mass, muscle growth and gain weight you need to eat more than what your body will burn in a day. Does this mean you can eat whatever junk food you like and still get to where you want to be? If you eat junk food then you are likely to increase weight and body fat as opposed to just gaining lean muscle tissue! In my opinion the cleaner and healthier the foods the better it is going to be for you.
So in order to grow you MUST eat more so that there is a surplus of calories for your body to work with. With this said, make sure you keep it healthy and clean. The better your choice of food is the leaner and better you are going to look. Want to grow, EAT more! A great way to compliment eating more is by using a weight gainer shake which has good calories in it. A popular choice is XL Nutrition Protein and Carbs which offers an extra 400 calories from protein and carbohydrates :)