While most people focus on losing weight, gaining weight can be just as difficult. Understand that a weight-gain diet is not one filled with fast food and milk shakes, even for those who are visibly too thin. Whether you need to gain pounds or lose them, it's important to include a variety of healthy foods from all the food groups. Eating the right foods ensures that you gain more muscle and not fat.
Estimate your calorie needs for weight gain. First, you need to determine your total energy expenditure (TEE). For thin men, multiply your weight in pounds by 11, and for thin women, multiply your weight in pounds by 10. Then multiply this number by an activity factor. If you get very little activity, use a factor of 1.3; if you get a little exercise or have a job that requires standing, use 1.6 if you're a man and 1.5 if you're a woman; or if you are moderately active, such as with a light labor job, use an activity factor of 1.7 if you're male and 1.6 if you're female. Once you've determined your TEE, add 500 to this number for your total calorie needs for weight gain.
Eat five to six small meals a day. Eating smaller meals more often helps prevent you from getting too full, which might help you get in more calories and help you reach your weight-gain goals.
Balance your intake. Even though you need to eat more calories to help you fill out, the Academy of Nutrition and Dietetics says it's still important that you include a variety of foods from all the food groups, including fruits, vegetables, whole grains, protein foods and dairy products.
Add calories to your usual foods. For example, at breakfast make your oatmeal with milk instead of water; add cheese and avocado to your sandwich at lunch; and instead of steaming your veggies at dinner, saute them in olive oil.
Snack on high-calorie foods. Fruit and nut mixes, peanut butter on whole-wheat toast, cheese and crackers are all nutrient-rich, high-calorie snack options that can help you gain weight.
Drink your calories -- but in a nutritious way. While water is good for hydration, when you want to gain weight it's better to drink beverages that supply calories. Milk and 100 percent fruit juice make the healthiest drink choices. The Academy of Nutrition and Dietetics also suggests that you drink your fluids in between meals so that it doesn't affect your appetite during mealtimes.