What Causes Weight Gain in Teenage Girls?

Teenage girls are at a time when lots of things in their life are changing, including their own body and physical appearance. This can be tricky to navigate and decide which changes are normal and which to be concerned about, especially as a parent watching your child go through these changes. As teenage girls’ bodies change, their weight is also naturally going to be affected.

The main cause of weight gain in teenage girls is due to inactivity and increased food consumption. When food consumption outweighs caloric output, extra energy is stored as fat in the body which equals weight gain.

Keep reading for the reasons your teen may be gaining weight and what to do about it.

Why Do Teenage Girls Gain Weight?

There can be many reasons why a teenage girl is going through a period of weight gain. Puberty and growth spurts are the main reason for weight gain during the teenage years, but other habits can also affect weight gain.

Normal weight gain in a teenager can be anywhere from 5-15 pounds in a year. More weight gained than that may not be alarming, since all teens grow at different rates (don’t we all know some teens who grow 6 or 7 inches in a year??). Teenagers grow a lot and fast! If your teen is gaining 15-20 pounds or more in a year, that’s when you need to check in with their pediatrician and dietitian to get professional recommendations based on your teen’s growth patterns. It can be shocking, but even if your teen’s weight doesn’t fit “normal” categories, it may still be appropriate and normal for your teen. A healthcare professional can help you assess overall growth patterns.

Other reasons teenagers gain weight include:

  • Overeating
  • Inactivity due to too much screen time
  • Busy schedules resulting in poor food choices
  • Increased independence of food choices (driving, going out to eat)
  • Peer influence on food choices and body image
  • Thyroid problems
  • Bad eating habits- skipping meals, late night eating, social eating etc.
  • Eating too quickly and not listening to hunger cues
  • Boredom eating and unintentional grazing

It comes down to calories in the end, sometimes too many calories in and sometimes not enough calories out through exercise. Teenagers should be eating enough to provide energy for their body including the extra energy needed for physical activity, without consistently overeating which will result in weight gain. 

If your teen struggles with any of the above habits and seems to be trending upward in their weight, what can you do about it? The role of a parent is to be an example of healthy habits, create a healthy food environment, encourage your teen with good health choices, and communicate often. Complaining or nagging your teenager about their weight will not help, but will most likely harm your teen, hurt their feelings, and make things worse in the long run. We are surrounded by a diet culture and our teens are likely very aware and self-conscious about their changing bodies already and don’t need our criticism to make things worse. They need support, positive role models, and open communication. Parents are the best examples for a teenager to learn healthy habits from.

Check out my post for some tips: How Can a 16 Year Old Lose Weight Fast?

Does Puberty Cause Weight Gain In Teen Girls?

Physical changes are normal as teenage girls develop into adults. Teens tend to grow taller and slimmer and then fill out and gain weight during and after puberty. It’s normal and completely expected. Growth spurts and hormone changes in puberty can result in weight gain or fluctuations. During puberty, estrogen is increased in the body, resulting in growth in hips and breasts as more fat is stored in those areas. Teenagers will also gain weight as they grow taller during puberty. These are normal changes and should not be worrisome as long as youth are following a growth trajectory as estimated by their growth charts.

It can be normal for teenagers to have increased appetites to affect weight gain as they are going through growth spurts and puberty as well. But regular overeating without increased activity will lead to weight gain.

What is a Healthy Weight for a Teenager?

Every teenager is different and the number on the scale is not what is most important, but the overall health and body composition of a teen is what will give you a better picture.

Teenagers should maintain a healthy body composition and weight for height. Body Mass Index or BMI, gives a general idea of how much body fat you have for your height. BMI is a screening method that is accurate in most cases at determining a person’s weight group. BMI is commonly used for adults and is assessed slightly differently for children and teens ages 2-19 by using growth charts and percentiles.

For adults, BMI is calculated from height and weight and a result between 18.5- 24.9 indicates normal weight, while over 30 indicates obese, and under 18.5 is underweight.

Use this BMI calculator for children and teens:


For teens, height and weight are plotted onto a growth chart and then assessed to find the corresponding BMI-for-age percentile for your teen’s age and gender. Check out the calculator to see where your teen falls.

For children and teens, a BMI-for-age percentiles are categorized as follows:

  • Underweight= less than the 5th percentile
  • Healthy Weight= 5th percentile up to 85th percentile
  • Overweight= 85th percentile up to the 95th percentile
  • Obese= 95th percentile or greater

It’s important to note that two teenagers may be the same weight, but different heights, and so will be in a different BMI percentile. The number on the scale should not be important as long as teenagers are maintaining a healthy BMI percentile based on their growth rate.

Developing healthy habits in the teenage years is important regardless of BMI. For overweight and obese teens, see your doctor or dietitian and only approach weight loss under their care and guidance.

When Should Parents be Worried About their Teenager’s Weight?

Body changes including weight gain during teenage years can have an effect on a teenager’s self confidence. This means weight gain should be addressed sensitively by parents. But when should you say something and intervene as a parent?

Some weight gain should not be alarming to teenagers and parents. The pattern of weight gain is more important than the amount of weight gain. If a teenager is maintaining a healthy BMI and not gaining weight too quickly, nothing should be brought up. Parents should not talk about their own weight or their teen’s weight, especially not negatively. You should only be worried if continual weight trends plotted on a growth chart over time are concerning. Follow up with your teen’s pediatrician or doctor at every regular yearly checkup to assess growth trends. If a teen is still going through growth spurts, it’s best not to say anything. Their weight will likely regulate over time. If a teen is developing unhealthy habits and plotting too high on a growth chart over and over again, it may be time to think about some changes.

When is A Teen’s Weight Concerning?

  • Sudden weight gain that does not stop
  • Rapid weight gain
  • Consistently gaining more than 2-4 pounds per month
  • Overeating without enough physical activity
  • Unexplained weight loss in healthy teens

Healthy habits such as physical activity and eating a balanced diet develop early, making it important to help your teen learn these skills. This starts by modeling the healthy habits you wish your teen to have, such as a healthy diet, regular physical activity, enough sleep, and a positive body image.  

How to Help a Teenager Make Good Food Choices so They Don’t Gain Extra Weight

Teenagers typically have a busy lifestyle with school and activities and the pressures and responsibilities of adulthood looming. As they are away from home more often, they have more control and independence of their food choices than they do at home. Friends also will have an effect on what food choices they have.

Food that is readily available at school and on the go such as in vending machines and drive thrus is generally not as nutritious and may result in too many calories consumed. Teenagers need to make sure they are getting enough food AND nutrients to provide enough energy for them during the day. If they have access to healthier options they are more likely to choose those, especially when they are very hungry.

Help teenagers have access to healthy snacks that are easy to take with them and have as a quick snack. Such as:

  • Trail mix
  • Hummus, veggies, and crackers
  • Cut up fruits and vegetables
  • String cheese
  • Portable natural peanut butter packets with pretzels
  • An energy bar such as a LARABAR
  • Protein fruit smoothie in reusable smoothie bottle
  • Dried fruit and fruit leather
  • Greek yogurt with granola and fruit
  • Rice cakes with nut butter and banana slices
  • Portable applesauce pouches
  • Whole wheat cereal with milk
  • Overnight oats
  • Cottage cheese and fruit
  • Veggies and dip
  • Whole wheat muffins
  • Lightly flavored popcorn
  • Salads with dressing
  • Pasta salad

For those times when you don’t have snacks readily available, teach your teenager how to make good food choices at restaurants and social events. Focus on filling half the plate with fruits and vegetables and only eating small amounts of the “favorite foods” that are typically high in calories, sugar, sodium, and fat. Teach and model to them how to eat enough food without overeating, and choose options that will keep them full. 

Tips for Helping Your Teen Make Good Food Choices:

  • Make sure your teen isn’t skipping meals because that can lead to unhealthy cravings and overeating later in the day
  • Meals should focus on protein, healthy carbs, and veggies
  • Limit processed foods and fast food
  • Model a healthy relationship with food
  • Cook and plan meals together when possible
  • Keep healthy food easily accessible- healthy snacks in the pantry and cut up fruits and vegetables in the fridge

Weight gain is not necessarily something to stress about, but healthy habits should be important no matter your teenager’s size.

Related Questions

How Much Weight Should a Teenager Gain Each Year? It’s normal for teenagers to go through growth spurts and put on pounds quickly. Normal weight gain in a teenager is about 5-10 pounds per year. However, your teenager may not fit the “normal” mold and still be perfectly healthy. The most important part of weight classification is overall trend on a growth chart.

How Can a Skinny Teenager Gain Weight? There are some teenagers who fall into the “underweight” category on a growth chart and can’t seem to gain weight. For health reasons some of these teens may be encouraged by a health professional to gain weight. To healthily gain weight a teenager should eat regular meals and snacks, get 15-30 grams of protein at every meal and snack, always eat until comfortably full, switch to 2% or whole fat dairy products, add dressings/dips/sauces to foods, use butter for cooking, always have healthy snacks on hand, and learn to listen to hunger cues. Check out: How Do I Get My Teen to Eat More? for more tips.

What To Do About Unexplained Weight Gain in Teenage Girls? With all the changes of puberty in the teenage years, there may be some extra unexplained weight gain. This should only be alarming if a teen has gained more than 5-10 pounds in a short period of time, has had a large decrease in physical activity, and/or has increased food consumption. Check in with the pediatrician and dietitian to assess next steps to take and see if there are any underlying problems. Check out: How Do I Get My Teen to Eat More? for more tips.

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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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