For some people, gaining weight is important for health. You may want or need to gain weight if you’ve always been underweight, are losing weight unintentionally, or have an eating disorder. You may also want to gain weight if you’re weight lifting and trying to gain muscle mass.
In some cases, losing weight quickly or being underweight could be signs that you’re malnourished or have an underlying health issue.
It’s important to gain weight safely. Some supplements marketed for weight gain could be contaminated with unsafe ingredients or have dangerously high amounts of protein or caffeine. Dietary changes are most beneficial for gaining weight, but reputable supplements may also help.
Clinically, being underweight means having a body mass index (BMI) lower than 18.5. However, in 2023, the American Medical Association issued new guidelines stating that BMI is a clinically imperfect measure. One of the flaws is that BMI doesn’t account for genetic or metabolic factors that impact body weight. Someone may be underweight due to genetics, which might make it unrealistic to gain and maintain a higher weight.
Someone may also be underweight due to poor nutrition. That could happen from a lack of food resources, extreme dieting, an eating disorder, or an underlying health issue that causes low appetite or nausea. A medical issue like a thyroid disorder, cancer, or digestive disease could also cause someone to become underweight.
Being underweight from poor nutrition could lead to nutrient deficiencies, a weak immune system, osteoporosis (brittle bones), anemia, depression, irregular periods, reproductive issues, and possibly premature death.
To gain weight, it’s important to increase your calorie intake. Your body uses calories in three main ways:
- Basic metabolic functioning: The energy your body needs to keep you alive, even while at rest
- Physical activity: Any way you move throughout the day, including working out
- Thermic effect of food: Digesting food and absorbing nutrients
If you don’t eat enough calories, your body will not have enough energy to perform all three functions well. Alternately, if you eat more calories than your body needs to accomplish those three functions, you may gain weight. This is called a calorie surplus.
You may need a larger calorie surplus than you expect if you are malnourished. This is common in people with anorexia nervosa who often experience weight gain resistance. Your body needs to catch up on all the nutrition it’s been missing, so it may take more calories than is typical to gain weight.
There is no one-size-fits-all recommendation for how many calories to eat for weight gain, so it’s best to speak with a healthcare provider for individualized guidance.
Making changes to your diet is the simplest way to gain weight. However, it’s important to choose nutritious foods to support overall health. There are a few ways you can adjust your diet to promote weight gain, including eating at consistent meal times throughout the day and focusing on nutrient- and calorie-dense foods.
Eat Regular Meals and Snacks
Eating regularly throughout the day is important to meet your calorie needs. Don’t skip meals, and make sure to add snacks to your day. Eating three meals and between one and three snacks per day is generally recommended.
Your hunger cues may be dulled initially, particularly if you have an eating disorder or have been skipping meals for some time. You may also feel full quickly. This is normal, but it doesn’t mean you shouldn’t still eat regularly. It may help to set a regular eating schedule for yourself to help your body adjust to eating enough for weight gain.
Eat Low-Volume, Energy-Dense Foods
Sometimes, increasing the amount of food you eat can be daunting. You may have a low appetite or feel full quickly. Eating low-volume, energy-dense foods can help increase your calorie intake without greatly increasing the size of your meals and snacks. Some ideas for this include:
- Cook vegetables in oil instead of steaming them
- Cook meat in oil or a creamy sauce
- Make smoothies loaded with fruit, vegetables, milk, chia seeds, nut butter, and protein powder
- Add mayonnaise, oil, pesto, or avocado to sandwiches
- Snack on nuts, full-fat yogurt, and granola
- Add caloric beverages like milk or juice to meals
You may also need to add meal replacement supplements like Boost or Ensure, which offer dense nutrition in a small package.
Add High Protein Foods
Eating more high-protein foods is important if you’re trying to gain lean body mass. Research shows that eating 2.2–3.4 grams (g) of protein per kilogram (kg) of body weight is most effective, especially when paired with resistance training.
High-protein foods that can help you meet this goal include chicken, fish, pork, beef, eggs, beans, lentils, peas, nuts, soy products, and dairy products.
You can also use protein powder, but choose a product that has been third-party tested for purity and potency to ensure it’s not contaminated with heavy metals or unsafe substances.
Be Mindful of Eating Too Much Fiber
Fiber is an incredibly important nutrient for digestive, cardiovascular, and metabolic health, but eating too much fiber can be harmful, especially when it comes to gaining weight. Fiber is not digestible, so it causes you to feel fuller faster. This could prevent you from eating enough calories to gain weight. Plus, high-fiber foods like fruits and vegetables tend to be low in calories.
Depending on the reason you need to gain weight, your healthcare provider may encourage you to limit your fiber intake and prioritize calorie-dense foods instead. This is especially common if you have an eating disorder and need to restore weight.
Strength training paired with adequate nutrition can help you gain muscle mass, which could lead to weight gain. Strength-training exercises include any movement where your muscles have to contract against an external load or resistance. You could accomplish this by doing bodyweight exercises, lifting free weights, using resistance bands, or using weight machines.
Strength training is especially important as you get older because muscle strength naturally decreases after age 30–35. Maintaining your strength and mobility as much as possible helps prevent cardiovascular disease and diabetes. It also helps improve sleep and reduce symptoms of depression and anxiety.
If you’re struggling to gain weight due to mood disturbances, the mood-boosting benefits of resistance training may indirectly promote weight gain. As your mood improves, you may have a greater appetite and a more consistent eating pattern.
Faster weight gain is necessary to prevent the harmful health effects of malnourishment in certain cases, such as weight restoration for an eating disorder.
However, if you are severely malnourished, be careful about increasing your calorie intake too quickly, as you may be at risk for refeeding syndrome. This is a dangerous shift in electrolytes and metabolic health that can occur from increasing calorie intake after a prolonged period of malnourishment. Refeeding syndrome can result in potentially fatal cardiovascular and neurological disruptions.
When gaining weight to treat malnourishment, an eating disorder, or another underlying condition, it’s best to work with a healthcare provider or registered dietitian. They can determine an eating plan that suits your specific health needs and is safe for you.
If you think you could benefit from gaining weight, a healthcare provider can help address your concerns and give guidance on the best way to promote weight gain.
There are a few signs that can indicate you or a loved one need to gain weight or should seek medical help regarding weight gain. For instance, if you lose over 5% of your body weight within one month or 10% in six months, you should see a healthcare provider right away. Other signs may include:
- Extremely restrictive eating, in quantity or types of food
- Brittle hair and nails
- Low blood pressure
- Slowed pulse or breathing
- Missed periods
- Constantly feeling cold
- Getting sick often
- Constantly feeling sluggish or tired
- Sunken cheeks, eyes, and temples
- Protruding ribs or pelvic bones
Some of these signs could indicate a different health issue unrelated to weight, but they could also signal that you are malnourished or at too low of a weight for your body.
If you have been implementing dietary changes and still aren’t gaining weight, speak with a healthcare provider. They can help assess why you aren’t gaining weight and tailor your plan for reaching your weight gain goals.
Whether you have an eating disorder, have always been underweight, or are trying to put on muscle, there are several strategies you can use to help gain weight. The simplest way to gain weight is to make dietary changes. Make sure to eat regular meals and snacks throughout the day, and try to eat low-volume, energy-dense foods to reach a calorie surplus without feeling too full too quickly.
To gain muscle, it’s especially important to eat plenty of protein. Pairing strength training with a calorie surplus can also help you gain muscle and support weight gain. A healthcare provider can offer individualized guidance on the best weight gain plan for you.