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Why Girls Gain Weight (From Prepuberty through Adolescence)

When your girl is gaining weight, it can cause you to worry. Learn why this happens by understanding the most common reasons a girl gains weight.

As the mom of four kids (three of which are girls) who have moved through the teen growth spurt, I’ve had firsthand experience with growing teenage girls and weight gain.

In my practice as a pediatric nutritionist, teen girls (and their parents) oftentimes show up with concerns about weight.

In this article, I highlight the most common reasons why girls gain weight.

Often, parents are looking for a medical reason for weight gain, such as low thyroid (hypothyroidism), but in my experience, this is less common. 

Even so, most pediatricians and other healthcare providers will want to rule out a medical basis for rapid weight gain.

More often than not, though, weight gain before and during puberty is related to a teen’s stage of development, lifestyle, and/or daily food and eating habits.

Normal Weight Gain versus Rapid Weight Gain

First, let’s clear something up. Weight gain is supposed to happen in girls. When a girl gains weight, it’s very likely to be a sign they are growing and developing. In other words, it may be perfectly normal.

Until the weight gets distributed and situated, the whole situation can look and feel awkward.

If you look at the growth chart, you’ll notice a surge in the weight and height curves around the time of puberty and adolescence. This reflects the normal uptick in weight gain and height growth.

However, some teens gain too much weight, and too rapidly for their health. According to the Centers for Disease Control (CDC), 21% of 12- to 19 -year olds females carry too much body fat.

Extra, unhealthy weight is associated with high blood pressure, high cholesterol, pre-diabetes, orthopedic problems, and more. As a parent who may be worried about your girl, your first job is to do a reality check: Is this normal weight gain and growth, which you will see on the growth chart, or is this problematic?

A group of middle school girls in the most common reasons girls gain weight

Why is My Daughter Gaining Weight?

Let’s look at the possible reasons why your girl may be gaining weight.

1. A Normal Growth Spurt 

The female body morphs quite a bit during the pre-teen and teen years. Did you know during growth spurts in boys more muscle is gained, while girls gain more fat? Generally, girls get more curvy and boys get more muscular.

The timing of weight gain is something to note as well. The growth spurt ages differ for boys and girls. During the start of puberty, around age 10 to 12, girls begin to see a lot of body changes. They start menstruating around 12 ½ years.

Most girls have completed the majority of their growth by age 14 or 15, but this depends on when they started menstruation. Girls who are late bloomers will start their growth spurt later and finish later.

Weight gain is normal at peak growth times like puberty and should not be a cause for worry. If your daughter is experiencing normal weight gain, be as supportive as possible by focusing on my 7 strategies to support a teenage growth spurt

2. Poor Food Choices

In my own experience as a mom of daughters, I’ve witnessed how nutritious foods and healthy meals can get off track. Especially in the teenage years.

If your teen is driving, that adds another challenge to the situation. Teens who can drive often find themselves heading out the door to social events that involve food.

“I’m heading to meet my friends for coffee!”
 “We’re meeting for ice cream.”
 “I’m getting dinner with my friend…”

As a result, food choices may not be as nutritious as they can be.

For example…

  • Sugary drinks such as soda or flavored coffee drinks that pack a lot of calories, fat and sugar (not to mention caffeine).
  • Sweets and treats like candy and ice cream.
  • Fatty foods such as pizza, French fries and chips.

Having too many unhealthy foods in the diet disrupts the overall food balance and may contribute to extra weight. Of course, some of these foods are perfectly fine in the diet, and can be quite enjoyable.

It’s all about the overall balance.

3. Poor Eating Habits

Many of our eating habits are formed in the early years. That’s why I’m a stickler about using an eating schedule with regular meals and establishing boundaries with feeding kids.

[If you want to know the secret to success, it relies on using a diplomatic feeding style.]

As a result of increasing independence, I often see females change their eating habits. They want more agency over their lives and this can include decision-making around eating.

They may:

  • Skip breakfast
  • Eat a light lunch
  • Raid the pantry or refrigerator after school
  • Eat late at night
  • Use crash diets to lose weight

If these tendencies become habitual eating patterns, they can contribute to extra weight gain.

4. Less Physical Activity

Teen girls are generally getting less physical activity than they were twenty or thirty years ago. I find it disheartening that schools nix regular physical activity around middle school. It’s a time when our kids need it the most to help them balance their health, wellness and stress levels.

In high school, gym class is minimized to a few days a week and actual exercise may be less than that. Recess, or a break to encourage physical movement? Nope.

While some girls play a regular sport and engage in training during the week, studies show that even athletes tend to sit around (quite a lot) when they’re not training, potentially minimizing some of the benefits of exercise.

Even if you have a daughter who is not inclined to move, she can be encouraged to be physically active. Muscle strengthening activities to spike muscle gains, gentle yoga, or a walk outside are ways to move the body for mental and physical health.

Exercise helps boost metabolism (aka calorie burning) and build muscle, both factors in maintaining a healthy weight and optimal body functions.

5. Smart Phones and Computers 

Did you know that 20% of US teens spend 5 or more hours a day on their screens (computer, smartphone, tablet, and video games)? Social media and screen time are contributing to a more sedentary lifestyle.

One 2016 study found that teens who spent 5 or more hours using smartphones and computers were twice as likely to drink more sugary drinks and less likely to exercise.

6. Lack of Sleep 

Does your daughter stay up later and have a hard time getting up in the morning? During the teen years, the circadian rhythm shifts. This means all teenagers get tired later than they did when they were younger. As a result, they go to bed later.

Yet, due to early school start times, they may need to rise early. This shortens their total sleep time, which may affect their ability to regulate their appetite and eating. Additionally, growth hormones are released while sleeping, so getting enough rest is key to growing optimally.

A 2016 study showed that inadequate sleep, poor sleep quality and late bedtimes were associated with extra food intake, poor food choices, and weight gain in adolescents.

All teens function at their best when they get at least 8-10 hours of sleep each night. Obviously, getting enough sleep along with daily exercise and a healthy diet is the key to a healthy, growing daughter. Sleep is not a waste of time!

7. Weight Training 

Strength training and the muscle mass gains that come along with it means that an overall weight gain can occur. Muscle weighs more than fat (or adipose tissue), so it’s a healthy gain, not a weight gain that comes with an increased risk of medical conditions.

8. Mental Health Challenges

More and more, girls from preteen to teen are experiencing more mental health challenges. An anxious or depressed state may contribute to emotional eating or overeating.

9. Eating Disorder or Dysfunctional Eating Behaviors

Some girls gain weight because they have dysfunctional eating behaviors like sneak eating, or an eating disorder like binge eating disorder. Be on the lookout for changes in eating patterns, behaviors or attitudes about food. 

More Help for Feeding Your Child

Check out our workshops, classes and guidebooks to help you nourish your teen, inside and out.

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