The best way to gain weight is by eating enough calories and exercising regularly.

Here are some healthy ways to gain weight when you’re underweight:

• Eat More Protein. Eating more protein will help you build lean muscle mass. This means that you’ll burn more calories while you sleep. You should aim to consume at least 1 gram of protein per pound of body weight each day.
• Don’t Skip Meals. Eating smaller portions of food throughout the day will help you feel full faster. It’s also important to make sure you’re eating enough protein. Protein helps keep your muscles strong and healthy. When you’re underweight, you may feel full faster. Eat five to six smaller meals during the day rather than two or three large meals.
• Choose Nutrient-rich Foods. As part of an overall healthy diet, choose whole-grain bread, pasta, and cereals; fruits and vegetables; dairy products; lean protein sources; and nuts and seeds.
• Try Smoothies and Shakes. Don’t fill up on diet soda, coffee, and other drinks with few calories and little nutritional value. Instead, drink smoothies or healthy shakes made with milk and fresh or frozen fruit, and sprinkle in some ground flaxseed. In some cases, a liquid meal replacement may be recommended.
• Drink Water. Drinking water helps keep your body hydrated and healthy. It also helps flush out toxins from your system. If you’re not drinking enough water, you might feel tired, bloated, or even constipated.
• Make Every Bite Count. Snack on nuts, peanut butter, cheese, dried fruits, and avocados. Have a bedtime snack, such as a peanut butter and jelly sandwich, or a wrap sandwich with avocado, sliced vegetables, and lean meat or cheese.
• Add Extra Toppings. Add extras to your dishes for more calories — such as cheese in casseroles and scrambled eggs, and fat-free dried milk in soups and stews.
• Have an Occasional Treat. Even when you’re underweight, be mindful of excess sugar and fat. An occasional slice of pie with ice cream is OK. But most treats should be healthy and provide nutrients in addition to calories. Bran muffins, yogurt, and granola bars are good choices.
• Add Some Exercise. You should aim to drink at least eight glasses of water each day. This will help you stay hydrated and avoid feeling thirsty. If you’re looking to lose weight, try adding some exercise to your routine. A good workout will boost your metabolism and burn calories throughout the day.