How Can Thin Girls Gain Weight?

One of the most beautiful things about bodies is that each one is different! If you have a desire to change your weight, the first thing you must do is develop a loving, respectful relationship with your body. Then, with the help of a dietitian, you can look into ways to use food to better nourish and take care of your body!

Gaining weight might be an appropriate option for some girls. I encourage anyone that wants to change their weight to talk with a registered dietitian to make sure their individual needs are met and give more individualized advice. Generally, thin teenage girls can gain weight in a healthy way by eating regularly and frequently, and consuming plenty of calorie-dense and nutrient-dense foods. 

Read on for more information about who should gain weight, tips for gaining weight for females, and how to eat if you have a fast metabolism.

Who Should Gain Weight?

There are quite a few reasons that girls might want to or need to gain weight. Here are just a few potential motivations:

  • They want to increase their muscle mass for improved sports performance.
  • They want to better support their hormone levels and keep a safe level of body fat available for their body to function at its best!
  • They want to give their body all of the nutrients that it needs to support growth and development.
  • They have lost their period. Females should absolutely see this as a sign that they are probably not eating enough and should reach out for help as soon as possible!
  • They want to feel better overall and they are working with a dietitian and doctor who agree that weight gain will help with energy levels and overall wellness.

What is a Healthy Weight for Females?

A healthy weight looks different on everyone and cannot be determined by a number alone. Body frame, body composition, gender, height, and genetics all influence what weight is appropriate for you. 

Healthcare providers will often track your weight over time and classify it as underweight, normal weight, overweight, or obese based on Body Mass Index (BMI) and the growth charts put out for the Center for Disease Control and Prevention (CDC). These classifications are shown in the table below:

It is important to remember that these classifications are not perfect and there are many other factors that need to be considered when determining a person’s health status. Additionally, those that are classified as a healthy weight by BMI might not actually be at a healthy weight when considering all factors.

It is important that a doctor track your weight and evaluate your lifestyle and habits to determine if something else is at play. Being underweight is not always a result of just eating less food. Clinical issues like Crohn’s Disease, Celiac Disease, overactive thyroid, and others can also result in a low body weight and need extra medical attention.

Ultimately, a healthy weight is one where you feel your best and can function at your full capacity. A healthy weight is also one where your body gets all of the nutrients that it needs. 

Best Tips for Gaining Weight for Females

A desire to change how your body looks can quickly become obsessive and can even lead to disordered eating, which is definitely not healthy! If you want to gain weight in a healthy way (for both your body and mind), I encourage you to get some personalized help!

On top of getting help from a dietitian that can guide you along the way, here are some tips I share with girls that want to gain weight in a healthy way!

  1. Eat frequently throughout the day and consume a balance of carbohydrates, protein, and fat. Skipping meals or going a long time without eating makes it challenging to get in the energy that your body needs.
  1. Include protein every time you eat. It is better for your body when it is spaced throughout the day. 
  1. Include healthy fats in your meals and snacks. Fats are very calorie-dense and help you boost the calories you are eating without making you feel like you have to eat a gigantic quantity of food.
  1. Keep snacks with you at all times so that you can immediately honor your hunger cues and eat regularly, even when things come up and throw you out of your normal routine. This might mean keeping food in your locker at school, in your car, at your desk, or other places that would be helpful!
  1. Set reminders to eat! Some people do this by setting an alarm on their phone. Others put sticky notes in places they will be sure to see them. Until eating regularly becomes more of a habit, setting reminders to check in with your body and eat something if it has been a little while is a really helpful tool!
  1. Pay attention to how you feel. If you are starting to give your body more fuel, notice how it is responding. If you are feeling more energized and satisfied, this is probably a sign that you are going in the right direction!
  1. Don’t be afraid of liquid calories. Include more liquids like milk, 100% juice, and smoothies to quickly and easily boost your energy intake.
  1. Have a bedtime snack! Our society has made it seem like eating before bed is a bad thing, but in reality, your body might need a snack between dinner and bedtime! Aim for a higher protein snack to help improve sleep quality. 

What to Eat to Gain Weight in a Healthy Way

While it might be easy to just eat a bunch of calorie-dense fast food and treats, there is more to it than just that. Your body still needs lots of nutrient dense foods and a good balance of carbohydrates, protein, and fat to feel good and gain weight in a healthy way.

I encourage people to start with eating frequently throughout the day, and making sure they are getting a good source of carbohydrates and protein every time they eat. Then, you can really focus on adding in more healthy fats!

So what are healthy fats! If you are looking at the nutrition facts label, you will want to look for foods that have high amounts of monounsaturated fats and polyunsaturated fats, low levels of saturated fats, and no trans fats. 

Healthy sources of fats that I encourage people to include more of are:

  • Nuts and seeds
  • Nut butters
  • Oils, especially olive oil and canola oil
  • Avocado and guacamole
  • Fatty fish like salmon

If you still can’t quite picture how to bulk up the meals and snacks you are eating, here are just a few examples and ideas.

Best Tips for Teen Girls to Gain Weight in a Healthy Way

  • Add peanut butter and walnuts or chia seeds to oatmeal for a satisfying breakfast!
  • Make protein bites with nut butter, oats, seeds, nuts, and anything else you want to add!
  • Cook veggies in a generous amount of olive oil. Additionally, you could drizzle oil over the top of cooked vegetables.
  • Peanut butter or almond butter make a great addition to things like toast, crackers, fruit, bagels, english muffins, smoothies.
  • Peanut butter can also be used to make a calorie-dense yummy peanut sauce that goes great over veggies, chicken, noodles, and more!
  • Power pack smoothies with lots of calorie-dense and nutrient-rich foods. Include a combination of seeds, nut butters, fruit, milk, avocado, greek yogurt, and green leafy vegetables.
  • Add berries and granola with nuts and seeds to greek yogurt for a quick and easy nutrient-dense snack.
  • Add avocado to soups, salads, burgers, quesadillas, sandwiches, wraps, burritos, rice bowls, smoothies, dressings and dips, and more!
  • Snack on nuts and dried fruit for a calorie-dense snack that is also balanced with carbohydrates, protein, and fat!
  • Top meals off with a sprinkle of cheese, or use cheese sticks, spreadable cheese, or prepackaged cheese squares as a snack paired with crackers, pretzels, wheat thins, or another carbohydrate food that sounds good to you!

How Can You Gain Weight if You Have a Fast Metabolism?

If someone has a fast metabolism, it means that the amount of energy their body needs to stay alive and maintain baseline bodily function is higher than it is for the average person. 

Your metabolism can be impacted by many things. Genetics are one of the biggest determining factors of your metabolism. However, your metabolism can change over time, naturally with age, but also as your body composition changes. 

Muscle mass is very metabolically active, meaning it uses a lot of calories even at rest. This is why many athletes might have a higher metabolism than others! 

Having a high metabolism means that you need to be really on top of getting in enough food to support your body’s needs! This means eating frequently throughout the day and including nutrient-dense and calorie-dense foods and healthy fats at every eating occasion.

Remember that there are clinical issues that could speed up your metabolism, so it is always a good idea to check with your doctor and keep them informed about what is going on with your body so that you can get the help you need.

How Fast Can I Gain Weight?

The rate at which you should gain weight will be different for each person, depending on their overall needs and goals, but regardless, gaining weight will take consistency and time. 

Work with a dietitian to make an eating plan that works for your specific needs, but remember to be patient with yourself and with the process! Remember that you can still love and respect your body no matter what your weight is. Focus on nourishing and taking care of your body!

How Can Girls Build Muscle?

Some girls are afraid to build muscle because they don’t want to “bulk up” too much. However, rest assured that just because you work to increase your strength does not mean you will turn into the incredible hulk! There are smart ways to tone and tighten without bulking up.

Working on building muscle and increasing strength is a great way for girls to also strengthen bones and promote healthy joints. It can also be helpful for sports performance as well as your ability to perform normal daily activities.

Gaining muscle is not about eating as much protein as possible. Eating protein is an important part, but your body still needs a proper balance of other nutrients and a calorie excess (meaning you have to be eating more calories than your body is burning). 

Another important part of building muscle is doing muscle strengthening activities! This does not necessarily mean going to the gym and lifting weights – although you can talk to your doctor if lifting weights is something you are interested in! They can make sure it will be healthy for your growing body and point you in the direction of someone who can help you lift weights in a safe way.

Girls wanting to build muscle will benefit from many of the weight gain tips listed earlier in the article! You don’t need to eat as many calories as humanly possible to gain muscle. In fact, just adding in a little bit extra energy for your body to build with is usually sufficient. I encourage anyone that wants to build muscle to work with a dietitian that can help determine an eating plan that will help you meet that goal.

One of the most important eating concepts for building muscle is timing your protein intake appropriately and eating protein (as well as carbohydrates and fat) regularly throughout the day. 

Consuming protein immediately after a workout can help your body repair and build muscle. I see many teenagers go crazy with protein intake, but girls probably only need around 10-20 grams of protein at a time. 

How intensely you are pushing your body might change your protein needs, but it is generally recommended that girls consume 10-30% of their daily calorie needs from protein. The RDA for protein intake for teenage girls is 46 grams per day, but athletes and girls that are really trying hard to increase their muscle mass might need more.


The best way for girls to ensure they are gaining weight in a healthy way is to enlist the help of a dietitian! They can help make a plan that works for you and that doable and enjoyable. 

Girls that want to gain weight should be eating regularly throughout the day, and should be consuming a balance of carbohydrates, protein, and fat. They should include moderate amounts of protein each time they eat rather than eating huge amounts at once. They can also focus on bulking up their meals and snacks by including energy-dense and nutrient-rich foods, and especially healthy fats like oils, avocado, nuts, fish, and seeds. 

Body respect and love should ALWAYS be given to your body, even if you aren’t satisfied with your weight. Teenage girls are especially at risk of developing unhealthy and disordered mindsets and eating and exercise habits, so they should seek out help to make sure they are on the right track!


Castle J. How teen athletes can build muscle with protein. Published July 21, 2020.

Life Time Training. 7 body and mind benefits of building muscle.

Katherine Harmer, RDN

I'm a Registered Dietitian Nutritionist with a love for coaching others to success in their health goals, especially teenage athletes. Tennis was my sport of choice in high school. Now I'm a little bit older, a little bit smarter, and a little bit worse at tennis.

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