The answer: Intentionally gaining weight is tricky because if you simply eat more food, you’ll end up feeling overly full and sluggish—which is no good. Luckily, there are three smart ways to go about gaining weight, says Young. First, eat more high-fat foods. But make sure to focus on healthy monounsaturated fats, not the saturated kind. “Don’t just load up on butter and full-fat cream cheese because that’ll leave you feeling gross," says Young. “Plus, those fats are bad for your overall health. Rather, snack on more nuts throughout the day, eat avocados with nearly everything, and put more olive oil on your salads and your breads.”
Another option: Drink more juice. But we’re not talking about drinking juice and nothing else—we’re talking about having the sweet drink with your meals, as opposed to eating the whole fruit or just opting for water or tea. “Usually, we tell dieters to skip the O.J. and have an orange instead because it’s fewer calories,” says Young. “But if you’re trying to gain weight, you’ll get the extra calories from the juice without feeling too full.”
And finally, continue to exercise—but focus more on weights and building lean body mass than you normally do. “Easing up on the cardio for a bit and directing more of your efforts on strength training may help you pack on healthy pounds because you’ll be building muscle,”
This is what another doctor says;
"If you are comfortable, able to function and exercise, weighing a little less than your ideal body weight is not a problem and studies show it is associated with good health outcomes," Escott-Stump says.
However, if you want or need to gain weight, do it the healthy way -- which is not about bellying up to an all-you-can-eat buffet.
Calories Count, But So Do Nutrients
Focus on healthy foods to gain weight, because even though you have more leeway with calories, good nutrition still rules.
"Weight gain requires eating calorie-rich but also nutrient-rich foods -- not just high-calorie foods with lots of fat, sugar, or empty calories," says Alice Bender, RD, nutrition communications manager for the American Institute for Cancer Research.
The goal is to choose foods that are packed with vitamins, minerals, nutrients, and calories so each bite is loaded with good nutrition.
"Start with nutritious foods and then wherever you can, enrich the foods with additional ingredients like yogurt, fruit, nuts, and healthy fats," Escott-Stump says.
Eat Often to Gain Weight
Regardless of why you want to gain weight, eating meals or substantial snacks (think mini-meals) more often is the way to pack more calories into the day.
"Try to eat six times a day, with each meal (or at least three of them) containing protein, starch, vegetable[s], and fat," says sports nutritionist and Georgia State University professor emeritus Christine Rosenbloom, PhD, RD.
A sample meal would include a turkey sandwich on whole-grain bread with mayonnaise and tomatoes and a fruit smoothie.
Eat often and choose wisely, and you can expect to gain an average of half a pound to 1 pound per week.
Gaining Muscle Mass
"Athletes who want to bulk up need to add sufficient calories and protein along with proper strength training to make sure they gain weight in the right places," Rosenbloom says.
She advises athletes to eat protein-rich snacks such as a high-protein energy bar, low-fat chocolate milk, or a protein shake immediately after weight training to give muscles the necessary post-workout fuel.
Rosenbloom instructs athletes to snack on high-calorie, high-protein foods and beverages, such as a protein shake with two scoops of whey protein before bedtime.
Avid exercisers who are not trying to build muscle mass also need frequent healthy snacks to fuel their physical activity and to maintain or gain weight.