Eat, eat, eat. You can gain calories by just eating more food. People tend to gain weight with meat because it's more calorie-dense than other foods, but you'd gain more weight by just eating more of less calorie-dense foods. Just keep it healthy - there's a difference between gaining muscle weight and just getting fat. And exercise as well, so you gain lean mass and not just get fat.
Eat more calories. Eat more calories than you burn at rest and through exercise. Do not give up your exercise, but concentrate on resitance exercise ( weight or weight machines) so you can build muscle. Avoid filling foods with few calories, ie popcorn, lettuce, etc. Eat more meat, cheese, and protein sources with fat. I do not recommend eating sugar/fat combo foods like ice cream or brownies.
Balanced diet. Though some patients augment their intake with high-calorie drinks (ensure) and bars, a cheaper approach would be to eat more nutrient-rich foods that ones enjoys as part of his/her diet. Consulting with a nutritionist would determine if a diet is balanced. In the meantime, following healthy eating guidelines from the cdc would be helpful http://www.Cdc.Gov/healthyweight/healthy_eating/index.Html. Read more...