You have to work hard to put weight on a naturally thin frame. Whether you have lost weight due to an illness or find it naturally difficult to keep on the pounds, being underweight can make you weak and vulnerable to illness. When you are too thin, you are also at a disadvantage when it comes to certain sports, and it can take a toll on your self-esteem. While you desire instant results and near-immediate changes in your appearance, gaining weight takes time. A fast, healthy rate of gain is about 2 pounds per week. Gain too much, too quickly, and you may find that you simply get fatter — not healthier and more muscular.
Gaining weight requires you eat more calories. You'll need at least 1,000 more daily than your body uses to maintain your current weight to gain 2 pounds per week. A simple way to fit these in is by doubling up your portions. Eat two cups of brown rice instead of one; prepare a second chicken breast; have an extra serving of cereal and milk. If each of your meals now contains between 300 and 500 calories, you'll easily add the 1,000 calories you need to gain weight.
Increase Calorie Density
If you can't imagine consuming a lot more volume of food, increase the calorie density of your current meal plan. Calorie-dense foods provide more energy per serving — for example, a cup of granola has almost 600 calories while a cup of corn flakes has just 114. Other swaps that result in increased calorie density include nuts instead of air-popped popcorn; raisins instead of grapes; chili instead of chicken noodle soup; avocado instead of mustard. Although healthy fat-containing foods, such as nuts and avocados, are often included in weight-loss plans, they can also help you gain weight because they contain concentrated calories. You are not exercising portion control as you would to lose weight; be generous with your servings -- for example, a cup of almonds contains about 800 calories. Other mealtime boosts include tossing pasta in olive oil before adding sauce, stirring dry milk powder into oatmeal or topping salads with sunflower seeds. Boost the calorie value of every meal during the day -- including two snacks -- by 200 to 300 calories, and you'll take in the extra 1,000 calories per day you need to pack on the pounds.
Three square meals is not good nutritional advice for someone trying to gain weight fast. Instead, you should be on a mission to snack often. Just because you're trying to gain weight doesn't mean you have license to grab a candy bar every few hours, though. Choose healthy, high-calorie snacks such as cheese sticks, trail mix and peanut butter. Include a pre-bedtime meal such as yogurt with almonds and berries, an almond butter and banana sandwich or a smoothie made with bananas, protein powder, milk and nut butter. Don't skip meals thinking you'll load up later. Your goal is to take in calories every two to three hours at least.
A high-calorie diet full of sugar, saturated fats and refined carbs will leave you sluggish and make you grow soft. Just because you are underweight doesn't mean you can eat anything you want -- you can still develop the chronic conditions that come about from poor nutritional choices. Fruits, root vegetables, whole grains and nuts are dense sources of calories that also provide a nutritional punch. Healthy weight is built in the gym as well as in the kitchen. Strength training two to three times per week with heavy weights on nonconsecutive days helps you develop lean muscle, which makes you look and feel better about your appearance. Feed your muscles as you train. A shake that combines healthy carbohydrates, such as milk, oats and fruit, with protein in the form of whey, soy or hemp replaces the calories you're burning as well as promotes muscle development. A modest amount of cardio, such as a light 30-minute walk or bike ride, can also stimulate your appetite so you can eat more.