If your Body Mass Index is less than 18.5, you are underweight. People with fast metabolisms, athletes, and people with certain diseases and disorders including diabetes, anorexia nervosa and certain thyroid disorders may need to modify their diet to gain weight. You can add more grains, fruits and vegetables, and high-protein meats and fish, to your diet to gain weight.
Grains and Nuts
Eating thick breads such as whole wheat and pumpernickel, and cereals with grape nuts, granola and oats can help raise your caloric intake. You may also supplement your meals with grains that are high in protein such as wheat germ and flax seed to gain weight. Nuts such as peanuts, almonds and walnuts are high in protein. Peanut butter spreads and nut spreads help you to include these nuts in your diet regularly.
Meats and Fish
Chicken and steak are high in protein, although it is recommended that you watch your intake of saturated fats while using these meats to control your weight. Lean-cut meats are suggested to avoid saturated fats and cholesterol, which may become detrimental to your health when consumed too frequently or in large portions. Salmon, trout, mackerel and tuna fish are great sources of protein that contain less saturated fat than red meats and poultry.
Adding more fruits and vegetables to your diet is a healthy way to gain weight. Eat fruits such as pineapple, bananas and avocados to increase your caloric intake. Raisins and cranberries are also ideal for healthy weight gain, as dried fruits are sometimes easier to eat in larger quantities than fresh fruits. Adding vegetables such as potatoes, corn, peas and carrots to your diet can help you gain weight, as these vegetables are high in carbohydrates and calories.