The health dangers of obesity are well known, but being underweight can compromise your health, too. Although less than 2% of U.S. adults over age 20 are underweight, having a body mass index (a metric used to gauge your body fat about your weight and height) under 18.5 can cause weakened immunity, fertility and hormonal problems, and nutritional deficiencies that can lead to anemia and osteoporosis[1]. What’s more, research suggests being underweight is linked to an increased mortality risk[2].
Whether you’re underweight or just looking to put on some muscle, it’s important to know how to gain weight—particularly lean body mass—in a healthy way.
Reasons to Gain Weight
Medical reasons for being underweight include long-term illnesses like cancer and recovering from eating disorders and thyroid or hormonal disruption, says Adam Atkinson, an International Sports Science Association (ISSA)-certified personal trainer and founder of See You Later Leaner in Columbus, Ohio.
“In my practice, I work with females with functional hypothalamic amenorrhea [the loss of a menstrual cycle due to a hormone imbalance] who want to get their hormones functioning optimally again,” he says. “I also get women going through pregnancy who need to have a controllable weight gain as well.”
Before beginning a weight-gaining regime, consult a licensed professional, adds Colleen Chiariello, a registered dietitian at Syosset Hospital in New York. “Some of the concerns associated with underweight status may be related to underlying medical issues,” she adds. “It’s recommended to get a physical with bloodwork and any additional testing to ensure the person is otherwise healthy.”
In addition to learning how to gain a healthy amount of weight for medical reasons, some people may be interested in “bulking up” or adding muscle, which also requires weight gain, according to Chiariello. Experts note that when you gain weight, you should aim to gain lean body mass specifically.
How to Gain Weight in a Healthy Way
When it comes to gaining weight, don’t rush it, experts say. Like weight loss, weight gain (particularly lean body mass) should be done gradually to allow the cardiovascular system to adjust, says Spencer Kroll, M.D., a board-certified internal medicine specialist at the Kroll Medical Group in Marlboro, New Jersey.
“Typically, one to two pounds per week is the maximum amount of weight gain that is indicated,” says Dr. Kroll. “Rapid weight gain can cause excessive stress on the cardiovascular system, leading to cardiac output problems.”
“This can cause blood pressure problems, fluid accumulation in the lungs and lower extremities and can also be toxic to the liver,” he adds. “Additionally, rapid weight gain can cause increases in adipose tissue.”
Before gaining weight, it’s best to seek your doctor’s advice, adds Mary Wirtz, a registered dietitian, a board-certified specialist in sports dietetics, and consultant for Fit Healthy Momma.
“Each individual is truly very different in terms of appropriate weight gain goals, and weight gain recommendations are contingent on a variety of factors including age, physical activity level, medical history, medications and more,” says Wirtz.
Atkinson adds that if it’s hard for you to gain weight, you may want to “consider staying slightly above a healthy body fat percentage [the percent of total body weight that is composed of body fat in proportion to lean mass, organs, tissues and water], because when you go back to maintenance mode, you’re probably going to drop some body fat naturally.”
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Increase Your Calorie Intake
Gaining weight requires a caloric surplus, and that means eating more calories than you burn each day, says Atkinson. Experts also suggest a gain in lean body mass typically requires a protein intake of at least 1.5 grams to 2.2 grams per kilogram of body weight per day.
Because each underweight individual has different nutrient needs, Atkinson also recommends going to a doctor who can evaluate your complete blood count results to check for vitamin B or iron deficiencies.
“Underweight patients often have individual B vitamin deficiencies such as low thiamine, folate and cyanocobalamin levels,” says Dr. Kroll. “They also have low iron levels and can have resulting anemia.”
If you find out that you do have nutrient deficiencies, you and your doctor can discuss whether it might be beneficial to start taking a supplement.
How Many Extra Calories Do You Need to Gain Weight?
Aim to add 300 to 500 calories per day above your maintenance caloric intake to gain weight in a slow, healthy way, advises Dr. Kroll and Wirtz.
Increasing calories slowly allows the body to adjust to caloric demand and thus provide needed energy for safe weight gain, says Chiariello, but the quality of those calories is still important. “Processed foods with high fats and calories are not the healthy choice and can lead to unwanted fat gain,” she says.
Focus on a Healthy Diet
For healthy weight gain, focus on wholesome foods, says Chiariello. These include:
- Whole grains, such as oatmeal and quinoa, which provide essential vitamins, minerals, carbohydrates and fiber.
- Fresh fruits and vegetables, such as spinach, broccoli and apples, which provide essential vitamins, minerals and fiber.
- Lean protein, such as chicken and fish , which provide amino acids for muscle development.
- Unsaturated fats like olive oil and avocado, which are excellent for heart health.
- Adequate fluid intake, specifically water, which is necessary for hydration and bowel regularity.
Overloading on unhealthy fats and sugars isn’t a good idea, even when trying to gain weight, as these food groups can lead to health conditions including high blood pressure and diabetes. “Foods that are fried, contain added sugars and/or salt or are not nutrient dense should be limited,” says Chiariello. “Reading food labels is valuable and provides insight on ingredients as well.”
Throughout the process of gaining weight, be sure to have your cholesterol and lipid profile monitored with regular bloodwork to make sure your levels are healthy, says Atkinson. He also advises using a glucometer to check your fasting blood sugar level to make sure it’s not too high.
Increase Your Protein Intake
To build muscle mass, people need around 2 grams of protein per kilogram of bodyweight, says Atkinson. “So if we were to calculate that for somebody who weighs 170 pounds, or 77 kilograms, they would consume 108 to 154 grams of protein a day,” he says.
What’s more, higher protein diets have been shown to promote muscle mass, prevent muscle loss and decrease the amount of muscle that is lost with aging, says Oluseun Olufade, M.D., a sports physician who works with a number of organizations and professional sport teams, including Emory University, the Atlanta Hawks and U.S. Soccer. “Protein can be consumed every three to five hours to help maintain muscle mass,” he says. “Food that contains 10 grams of protein include 40 grams of skinless cooked chicken, 50 grams of canned tuna, 120 grams of tofu, 60 grams of nuts, and 40 grams of cooked lean beef, pork or lamb.”
To up your protein intake, consider adding animal-based protein sources, such as poultry, fish, red meat, eggs, greek yogurt and cottage cheese, plant-based sources like beans and lentils, nuts, seeds, tofu, whole grains, and, in smaller amounts, fruits and vegetables, says Wirtz. Protein powders, shakes and bars are also easy sources of protein when on the go.
A health care professional can help you assess the correct amount of protein you need to gain weight based on your body type and needs.
Healthy Ways to Build Muscle
Individuals who are recovering from an illness or who have been sedentary for an extended period of time may have the goal of building muscle and gaining weight, says Dr. Olufade. “People may also have to build muscle and gain weight for a specific athletic competition or profession,” he says.
Exercise
For people looking to put on muscle mass, Atkinson says strength training is essential. “Anything that stimulates the muscle tissue is good,” he says. “Going to the gym four to five days a week is very important. But remember [to give] yourself off days to recover as well.”
To achieve weight gain and add muscle, weightlifting is more effective than cardio, says Dr. Olufade. This is because cardio tends to cause a person to lose weight due to burning fat. On the flip side, weightlifting builds the muscles, allowing them to gain lean muscle mass, he says.
Lifestyle Changes
Lifestyle habits also play a part in gaining weight. Everyone needs adequate sleep and rest to promote health and well-being, says Chiariello. “The body needs an opportunity to rest, which impacts muscle and brain functioning,” she adds.
To prevent hunger and keep the body’s metabolism active, Chiariello recommends eating small, frequent meals. Snacking before and after workouts also gives the body needed nutrients to perform optimally, she says. “Routine and ongoing exercise are needed for healthy weight gain, [whereas] a lack of exercise can lead to unhealthy weight gain,” says Chiarello.
Eating four to six meals a day is a great idea for someone trying to eat more, says Atkinson. “If you’re already eating that amount of meals, try to add in a few more calories per meal,” he adds. “Also, keep in mind you don’t just want to force-feed because that can result in digestive distress.”
Atkinson emphasizes the importance of relaxation during mealtimes. “It’s best to be in a calm state, chew your food really thoroughly and be mindful of your stress before meals,” he says. “If we are stressed and we get to that fight-or-flight state it definitely interrupts the parasympathetic ‘rest and digest’ [component] of eating.”