If you’re underweight and looking to gain weight, it’s very important to do it right.

Consuming soda, donuts, and other junk foods may help you gain weight initially, but it can increase your risk of heart disease, diabetes, and cancer (1, 2, 3).

A healthier approach to gaining weight involves gaining a balanced amount of muscle mass and subcutaneous fat rather than a lot of unhealthy belly fat (4).

A recent animal study suggests that belly fat specifically may be correlated with increased cancer risk (5).

A high percentage of body fat also increases your chances of developing type 2 diabetes and other health problems, even if you are not overweight (6, 7).

To gain weight healthily, focus on eating more nutrient-dense foods and living an overall healthy lifestyle that involves exercising, getting enough sleep, and reducing stress, if you can.

This article outlines simple strategies to quickly gain weight — without increasing your risk of disease.

Summary

It’s important to eat mostly healthy foods even when you’re trying to gain weight.

While about 74 percent of adults in the U.S. are either overweight or obese, there are also many people with the opposite problem of being underweight (8, 9).

Some individuals may be naturally underweight due to genetics or a fast metabolism. Being underweight may also be indicative of poor nutrition or underlying health conditions (9).

Additionally, many people who are not clinically underweight may still want to gain some muscle and put on weight for other reasons.

Whether you’re clinically underweight or simply struggling to gain muscle weight, the main principles are the same.

Being underweight is defined as having a body mass index (BMI) below 18.5. This is estimated to be less than the body mass needed to sustain optimal health (10).

You can use this calculator to see where you fit on the BMI scale.

However, keep in mind that there are many problems with the BMI scale, which only looks at weight and height. It does not take muscle mass into account.

Some people are naturally very skinny but still healthy. Being underweight according to this scale does not necessarily mean that you have a health problem.

According to the Centers for Disease Control and Prevention (CDC), being underweight is about twice as common among women, compared with men. In a U.S. survey that grouped participants into men and women, 1.3% of men and 2% of women 20 years and older are underweight (9).

Summary

Being underweight is defined as having a body mass index (BMI) below 18.5. It’s more common in women.

Being underweight can be harmful to your health.

One study found that clinically underweight individuals have nearly two times the risk of death compared to obese individuals, suggesting that being underweight may be worse for your health than being obese (11).

Additionally, another study found that self-reported health outcomes fell significantly in underweight individuals after the age of 38, indicating that a low BMI later in life may come with increased health risks (12).

Being underweight can impair your immune function, raise your risk of infection, lead to osteoporosis and fractures and cause fertility problems (13, 14, 15, 16).

What’s more, people who are underweight are much more likely to get sarcopenia (age-related muscle wasting) and may be at greater risk of dementia (17, 18).

For children, it can also lead to growth and development problems (19).

Summary

Being underweight can negatively affect your health. People who are underweight are at risk of osteoporosis, infections, fertility problems, and early death.

There are several medical conditions that can cause unhealthy weight loss, including:

  • Eating disorders: This includes anorexia nervosa, a serious mental health disorder (20).
  • Thyroid problems: Having an overactive thyroid (hyperthyroidism) can boost metabolism and cause unhealthy weight loss (21).
  • Celiac disease: The most severe form of gluten intolerance. Overall, the incidence of celiac disease has risen throughout the 20th and 21st centuries (22).
  • Diabetes: Having uncontrolled diabetes (mainly type 1) can lead to severe weight loss (23).
  • Cancer: Cancer can cause the body to be in a hypercatabolic state, which leads to increased energy being used. It can cause someone to lose a lot of weight but the severity and weight loss can depend on the type of cancer and the age of the person. (24, 25).
  • Infections: Certain infections can cause someone to become severely underweight. This can include parasites, tuberculosis, and HIV infection (26, 27, 28).

If you’re underweight, you may want to make an appointment with a doctor to rule out any serious medical conditions.

This is particularly important if you have recently started losing large amounts of weight without trying.

Summary

There are several medical conditions that can cause unhealthy weight loss. If you’re underweight, consider making an appointment with a doctor to rule out a serious health problem.

Whatever your reasons are for wanting to gain weight, there are a variety of strategies you can use to bulk up.

Below, we’ve outlined several different ways to help you gain weight.

Increase your caloric intake

The most important thing you can do to gain weight is to create a calorie surplus, meaning you eat more calories than your body needs.

You can determine your calorie needs using this calorie calculator.

If you want to gain weight slowly and steadily, aim for 300–500 calories more than you burn each day according to the calculator. If you want to gain weight fast, aim for around 700–1,000 calories above your maintenance level.

Keep in mind that calorie calculators only provide estimates. Your needs may vary by several hundred calories per day, give or take.

You don’t need to count calories for the rest of your life, but it can help to do it for the first few days or weeks to get a feel for how many calories you’re eating. There are many great tools out there to help you.

Summary

To gain weight, you need to eat more calories than your body burns. Aim for 300–500 calories per day above your maintenance level for slow weight gain or 700–1,000 calories if you want to gain weight fast.

Increase your protein intake

Adequate consumption of high quality proteins from animal products is essential for optimal growth, development, and human health (29).

A 2020 study of 23 individuals demonstrated that increasing protein will increase lean muscle mass (30).

To promote skeletal and muscle growth and physical strength in healthy adults with minimal to intense physical activity, the Recommended Dietary Allowance of protein is between 1.0 to 1.6 grams of protein per kilogram of body weight per day (30).

Up to 2 grams per kilogram of body weight of protein per day may be safe for healthy adults, with the upper limit at 3.5 grams per kilogram of body weight per day.

High protein foods include meats, fish, eggs, many dairy products, legumes, nuts, and others. Protein supplements like whey protein can also be useful it is difficult for you to get enough protein in your diet.

However, protein may also reduce your hunger and appetite significantly, making it harder to get in enough calories (31).

Additionally, eating too much protein may also increase your risk of heart disease (32).

Talk with a doctor to see if increasing your protein intake would help you achieve your goal to gain weight in a safe way.

Summary

Protein forms the building blocks of your muscles. Eating sufficient protein is required to gain muscle weight in addition to other nutrients.

Increase your intake of carbs and fat

Many people try restricting either carbs or fat when trying to lose weight.

This may make it hard to gain weight, as it will make it harder to get in enough calories.

Eat plenty of high carb and high fat foods if weight gain is a priority for you. It is best to eat plenty of protein, fat, and carbs at each meal.

You may want to avoid eating plans such as intermittent fasting. This eating plan can be useful for weight loss and other benefits but can make it much harder to eat enough calories to gain weight (33).

Make sure to eat at least three meals per day and try to add energy-dense snacks whenever possible.

Summary

To gain weight, eat at least three meals per day and make sure to include plenty of fat, carbs, and protein.

Increase your intake of energy-dense foods

It’s very important to eat mostly whole foods, like fruits, vegetables, whole grains, and legumes.

However, these foods tend to be more filling than processed junk foods, making it harder to get in enough calories.

Using plenty of spices, sauces, and condiments can help with this. The tastier your food is, the easier it may be to eat a lot of it. Toppings may also add additional calories.

Also, try to emphasize energy-dense foods as much as possible. These are foods that contain many calories relative to their weight.

Here are some energy-dense foods that may help you gain weight:

  • Nuts like almonds, walnuts, macadamia nuts, and peanuts
  • Dried fruit, including raisins, dates, prunes, and others
  • High fat dairy, such as whole milk, full-fat yogurt, cheese, and cream
  • Fats and oils like extra virgin olive oil and avocado oil
  • Grains, including whole grains like oats and brown rice
  • Meat, such as chicken, beef, pork, and lamb; you can also choose fattier cuts
  • Tubers, including potatoes, sweet potatoes, and yams
  • Other energy-dense foods like dark chocolate, avocados, peanut butter, coconut milk, granola, and trail mix

It may be a good idea to avoid over-consuming vegetables and fruit if gaining weight is a priority for you. The fiber in fruits and vegetables can lead you to feeling full faster. This can leave less room for energy-dense foods.

If you need more suggestions, these healthy foods may help you gain weight faster.

Summary

Base your diet on energy-dense foods as much as possible, as they contain many calories relative to their weight without processed sugars or unnatural ingredients.

Combining a high calorie intake with heavy resistance training may help you gain weight (34).

That being said, there are several other strategies to gain weight even faster.

Here are 10 additional tips for gaining weight:

  1. Avoid drinking water before meals. This can fill your stomach and make it harder to get in enough calories (35).
  2. Eat more often. Squeeze in an additional meal or snack whenever you can, such as before bed.
  3. Drink milk. Drinking whole milk to quench thirst can be a simple way to get in more high quality protein and calories.
  4. Try weight gainer shakes. If you are having trouble gaining weight, consider weight gainer shakes. These are very high in protein, carbs, and calories.
  5. Use bigger plates. Consider using large plates if you’re trying to get in more calories, as smaller plates can cause people to eat less (36).
  6. Add cream to your coffee. This is a simple way to add in more calories.
  7. Take creatine. The muscle-building supplement creatine monohydrate can help you gain a few pounds in muscle weight (37).
  8. Get quality sleep. Sleeping properly is very important for muscle growth (38).
  9. Eat your protein and fat source first. If you have a mix of foods on your plate, eat the calorie-dense and protein-rich foods first. Eat higher fiber foods like raw vegetables last.
  10. Avoid smoking, and if you smoke, consider quitting. Smokers tend to weigh less than non-smokers, and quitting smoking often leads to weight gain (39).
Summary

There are several other things you can do to gain weight faster. These can include drinking milk, using weight gainer shakes, adding cream to your coffee, and eating more often.

To gain weight, you’ll likely need to consume additional calories.

You can avoid overeating too much and make sure that the excess calories go to your muscles instead of just your fat cells by starting a resistance training program.

Resistance training, or strength training, includes both bodyweight exercises and free weights. Resistance training leads to muscle hypertrophy, which increases muscle mass (34).

Combining protein supplementation with resistance training can promote additional gains in lean body mass beyond those gained by resistance exercise alone.

One study found that protein supplementation during resistance training for six weeks increased lean mass growth by 27% in healthy adults (40).

If you’re completely out of shape or new to training, consider hiring a qualified personal trainer or taking a class to help you get started, if this is possible for you.

You may also want to consult with a doctor if you have skeletal problems or any medical issues.

To maximize muscle mass, it’s best to focus on resistance training over cardio (41).

Doing some cardio can help improve fitness and well-being, but you may want to avoid doing so much that you end up burning all the additional calories you’re eating.

Summary

Lifting heavy weights and improving your strength through resistance training can help you gain muscle mass.

By consuming 500 additional calories a day, a person might gain an average of about 15 pounds (6.8 kg) over 6 months (42).

A more aggressive approach of consuming an additional 1,000 calories per day may allow a weight gain of about 25 pounds (11.4 kg) over 6 months. However, a large portion of this weight gain may be compromised of fat (42).

It can be very difficult for some people to gain weight, and the amount of time it takes to gain weight will be different for everyone.

That may be because your body might have a certain weight, called a setpoint, where it feels comfortable. It’s theorized that whether you try to go under your setpoint (lose weight) or over it (gain weight), your body resists changes by regulating your hunger levels and metabolic rate (43).

When you eat more calories and gain weight, your body may respond by reducing your appetite and boosting your metabolism. This may be largely mediated by your brain, as well as weight-regulating hormones like leptin (43).

However, researchers have not proven or dismissed their theory and more research is still needed (43).

So you may encounter a certain level of difficulty.

Summary

The amount of time it takes to gain weight will be different for everyone, as your body responds to extra calories and weight gain by reducing your appetite and boosting your metabolism.

The bottom line

There are many reasons for wanting to gain weight.

It’s important to do so by eating nutritionally-dense foods and building lean muscle mass.

At the end of the day, changing your weight is a marathon, not a sprint. It can take a long time, and you need to be consistent if you want to succeed in the long run.

If you’re struggling to gain weight despite trying the strategies discussed above, it’s important to talk with a doctor or dietitian. A dietitian can help you employ eating strategies that may help you reach your goal.

Just one thing

If you may have an undiagnosed condition that’s causing your weight loss, it may be best to talk with a doctor before trying to gain weight using the tips above.