Fruit and Vegetable. Whatever you do, use healthy foods, like fruits and vegetables, to increase your size. Using starch in breads, potatoes, pasta and rice, or high sugar drinks is a mistake. Protein shakes often have more protein than you really need. Be careful you don't over-shoot your goal and set yourself up to spend the rest of your life on a weight reduction diet. Moderate exercise is a very good idea also.
Depends. We should first know what's preventing you gain weight.Has your thyroid been checked? Have you had some studies done to rule out occult malignanciesz?. If all the above is normal, then just eat right and healthy. If you don't have diabetes or cholesterol issues , you may increase your carbohydrate intake.