Just to gain muscle - no weight problem?
It's easy. Choose a good source of Protein, carbohydrate, and natural healthy fat (not hydrogenated or trans fats) with every meal. Eat 4-6 times each day. Include
green veggies with every meal. More sugary or starchy foods in the first hour after you
lift weights. This is where your fruits and more starchy foods like rice go with your protien source.
Good choices throughout the day are whatever meats you like, 100% whole wheat bread, oatmeal, brown rice, whatever green veggies you like to eat, potatoes - even sweet potatoes in the first hour after lifting are great.