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Teen Gaining Weight? 10 Sneaky Reasons for Teen Weight Gain

Many parents start to worry when they see their teen gaining weight. From rapid and unexpected weight gain to a slow and gradual filling out, there’s a lot going on during the teen years.

I’ve seen it over and over in my pediatric nutrition practice: teenage weight gain. Parents worry, but it’s not always something to be concerned about.

But, parents wonder if there’s something they should do about it. If they should somehow intervene and stop it. Many parents want to know how to handle teen weight gain without causing more problems, such as disordered eating or an eating disorder. 

Learn about teen weight gain and what you can do to help (without harming) in this article.

You’ll learn:

  • What is considered normal weight in teens
  • The common causes of too much weight gain
  • Ways to help the teen who is putting on extra body weight
Rapid weight gain in teens - how to help and not harm

Is Pre-Puberty Weight Gain Normal?

Yes, tween weight gain is a normal part of development. It’s expected that all tweens will experience a weight increase, called preteen weight gain. When you look at the total amount of weight gained across the span of the teenage growth spurt, it is significant.

That awkward, pudgy appearance many tweenagers go through is a completely normal part of puberty. Adolescent girls can gain fifteen pounds or more during puberty, while boys gain upwards of thirty pounds during this time.

[Read: When Do Girls Stop Growing?]

What Does the Average Teen Weigh?

The growth charts give you a sense of how your teenager is growing, and you can easily check it at your child’s next checkup. Although these growth charts have a median, or “average” weight for each age, using this as a marker to compare your child’s weight can be problematic.

Each child grows to his or her own potential. There really is no “average” teen weight or height. Teen growth is based on a genetic predisposition and the environment within which they grow up.

The first way to assess whether weight is becoming problematic is to look at your child’s individual growth pattern over time. One point in time won’t give you the information you need to realistically assess what’s going on.

Over the years, is your teen growing along the same channel as usual? If so, there’s nothing to worry about. Or, is he jumping up on the charts into a higher percentile channel? Then there may be excess weight gain that could be worrisome. (Keep reading!)

85+ Healthy Snacks for Teens!

What Causes Unintentional Teen Weight Gain?

Rapid weight gain can be caused by several things: a disturbance in hormonal activity of the thyroid, for example, can lead to fast weight gain. However, in many cases, rapid weight gain is a sign that extra calories, eating and activity is getting off track.

As a parent, there’s a fine line to walk when your teen, who is fairly independent with eating, starts to show signs of gaining weight. Should you do something? Or should you do nothing at all?

First, you need to understand what may be causing your teen to gain weight.

How Teens Grow and Gain Weight

According to Robert Malina, a researcher on childhood growth, adolescents gain weight and height in a predictable pattern. Height growth occurs first, followed by weight gain. I like to call this pattern “stretching out, then filling out.”

(This is different from childhood growth where pudginess often happens before increases in height.)

In teen girls, peak height growth occurs between ages 11-13 years. In boys, the peak height gain happens between 13 and 15 years, on average. The weight gain from lean tissue (muscle and bone) during this time is about 15 pounds for girls and twice that for boys (~30#).

Girls gain more fat (~6#) on average than boys (~3#).

[Read: When Do Boys Stop Growing?]

Given these “norms,” and the typical signs of the growth spurt that go along with it, you can begin to see that an important physical transformation happens for teens. A 15-30# gain in a couple of years can be shocking, especially if you’re used to looking at a lean child, but it is normal.

(Even if weight gain is beyond these “norms,” it can still be normal for your teenager, depending on genetics and your child’s historical growth pattern.)

What may not be normal is large meals and extra calories, both of which can cause unwanted and unhealthy weight gain. Another contributor: Lack of regular exercise. When teens aren’t active, it can promote an imbalance of energy. Meaning, energy consumed is greater than energy burned.

Read: How to Be a Fit Kid

teen girls eating pizza - what to do if your teen is gaining weight

What’s Behind Body Changes in Adolescence?

In 2020, about 20% (1 in 5) of children and teens aged 12-19 were classified as “overweight or obese,” terms that indicate an individual is carrying too much body fat, according to the Centers for Disease Control (CDC).

Note, some teens are genetically predisposed to carry more body fat. That’s a topic for another article, however, if you want to learn more about this, listen to my podcast interview with Ted Kyle. If your teen is gaining weight, here are some common reasons:

1. Independence and Calorie Intake

The increased independence associated with adolescence can lead to more eating. For example, a teenager with a new driver’s license may land in the drive thru lane. He may gather with friends at the local coffee shop. Or grab lunch and dine out more often.

Translated: extra calories.

2. Reduced Physical Activity Levels or a Sedentary Lifestyle

Teens may not get daily activity if they don’t play a sport and school-based physical education has been declining for decades. The opportunities for natural activity is less due to classroom schedules and lack of gym time.

This can slow metabolism and reduce daily calorie expenditure (also known as calorie burn).

3. Food Choices and Food Intake

Food choices may not be rooted in wholesome, nutritious foods. Fast food, ultra-processed foods, candy, and other unhealthy choices may be the norm rather than the rarity.

All these foods can contribute to a higher calorie intake.

4. Poor Eating Habits

Eating habits can also play a role. Late night snacking, skipping breakfast, and social eating can disrupt appetite regulation and add more calories.

5. Medical Conditions

Some medical conditions may cause unexpected weight gain, including hypothyroidism (low thyroid hormone), Cushing’s disease, and polycystic ovary syndrome (PCOS), to name a few.

Thyroid hormone is made in the thyroid gland and helps the body burn the energy (calories) it ingests. When there is inadequate thyroid hormone, the metabolism slows down and the chances for weight gain increase.

6. Insulin Resistance 

Insulin is a hormone that helps the body regulate blood sugar. When children and teens have excess body fat it may make their bodies less sensitive to insulin. This causes an elevation of blood sugar and an inability for insulin to help sugar enter into the cells. High levels of insulin circulating in the blood may cause extra hunger.

7. Lack of Sleep

All children and teens need a good night’s sleep. Studies show that when teens (and kids and adults) get less sleep than what is needed, they are at increased risk for gaining weight.

According to the CDC, children and middle school kids need about 9-12 hours of sleep and teens need at least 8 to 10 hours each night.

8. Hormonal Changes: Stress Levels

Some teens experience more stress, especially as they get closer to graduating high school and feel a pressure to figure out their next steps. 

The stress hormone, cortisol, can contribute to weight gain, especially in the mid-section. Cortisol levels that are chronically high may promote overeating and weight gain.

9. Menstrual Cycle

In girls who have their period, progesterone is produced during the cycle. Progesterone may cause water retention, which may appear as bloating, swelling and puffiness. This subsides after the period is over.

10. Mental Health Conditions

For adolescents who experience anxiety or depression, the motivation to exercise or eat healthfully may decline. Food can become a source of comfort. 

Teenagers who are treated with medications for depression or anxiety may experience the side effect of weight gain. All told, there are many reasons that teenagers may experience unwanted weight gain.

What to Do When Your Teen Has Extra Weight 

It can be hard to figure out why weight gain is happening. The first thing you want to do is assess whether your teen is going through her normal stage of growth and development. If weight and height seem to be progressing along a normal path, then you’ve got nothing to worry about (and nothing to say).

If there is a clear bump in your teen’s weight curve, indicating sudden or excess weight gain, I still believe you should say nothing about it to your teen. Why?

Because calling this out can be very disturbing and disruptive to a teen’s developing self-esteem and body satisfaction. Body dissatisfaction has been highlighted as a risk factor for dieting and other dangerous, weight-reducing efforts. It can also contribute to the development of an eating disorder.

What You Say to Your Teen Can Help or Harm

If you have concerns about your teen’s weight, tread lightly, particularly with what you say to them.

Starting on a tirade of what’s healthy to eat and what’s not, or extolling the virtues of exercise will likely be received as hurtful commentary.

Nagging your teen to exercise, or commenting on her appearance may do more harm than good. And, it’s unlikely to spur her to eat better or exercise more. In fact, it can make eating worse and turn your teen off from exercising!

Many teens are self-aware. They know their bodies are changing. They may be secretly unhappy or self-conscious about their weight or appearance. You may hear questions like, “Do you think I’m fat?”

Don’t panic if this happens. Many teens are simply looking for your reassurance and acceptance.

Should You Promote Weight Loss for the Teen? 

Weight loss diets aren’t a good idea. But it’s normal to wonder and think about this. We have a culture of dieting, and our teens are experiencing it, too.

The pursuit of weight loss with restrictive diets can lead to a lifetime of yo-yo dieting, poor self-esteem, and a higher risk for mental health problems. You can, however, help your teen move toward healthy eating patterns and lifestyle choices. And this is the safer path for all teens.

When Your Teen Isn’t Concerned about Weight

Your teen may not be as concerned about their body as you are. They may tune out your lectures about long-term health. An appointment with a dietitian or other health care provider, if not inspired by your teen, may be unsuccessful. It could even be damaging.

How to Help the Teen Who’s Gaining Weight (Without Harming Them)

Most parents can’t stand to watch their teen overeat, or sit around and be lazy. They want to do something about it! This often turns into nagging, inspirational discussions, or offers of help.

These direct interventions often fall flat with teens. The good news, though, is that there are plenty of things you can do to help your teen without harming her.

Here are four positive ways to encourage health:

Is your teen gaining weight? Here's what you can do to help

Create a Healthy Food Environment

You are the nutritional gatekeeper in your home. In other words, you allow food in. You choose it, purchase it, and stock it.

While you can’t do much about your teen’s eating patterns outside of your home, you can keep your homestead healthy and offer a nutritious, healthy diet.

Make sure you’ve got plenty of nutritious snacks and other items in your kitchen pantry and refrigerator. Place them front and center. Because teens are growing rapidly, they may have a voracious appetite and eat what’s available to them.

Stock up on healthy snacks such as yogurt, cut up fruit, vegetables, whole grain cereals and breads, nuts, seeds, popcorn and more. And stick with regularly timed meals and snacks, so overeating due to hunger isn’t likely to happen.

Be a Good Role Model Yourself

Show your teen what it means to eat nutritiously and exercise. Lead by example, not by talking about the virtues of being healthy or slim.

Remember, actions speak louder than words. Be what you want your teen to be: a good eater, a regular exerciser, and a good sleeper.

I know from my own experience as a mom of teens, what my teens see me doing day in and day out sets the bar for how they will conduct their daily lives.

Keep the Lines of Communication Open

Be non-judgmental and open to discussing your teen’s body and weight concerns.

Your teen may tell you that he is frustrated with his lack of muscle, or the appearance of his belly, or that they’re uncomfortable in their clothing.

That’s your lead in for a productive conversation. Your intention should be to help: “Is there something I can do to help with that?” is a good response to these concerns.

Just being available to listen without unsolicited suggestions can work wonders.

85+ Healthy Snacks for Teens!

Lifestyle Changes: Invite Your Teen to Join You

Often, teens are leading an independent life, hanging out with friends, studying on their own, and hardly around the house. When you can, invite your teen to go for a walk, to a movie, to the grocery store, to a local event, or to the gym.

An invitation to your teen is a sign you’re still interested in spending time together, which can go a long way in keeping the relationship strong and opportunities for communication and your influence alive.

For anyone who experiences weight gain, the motivation to change lifestyle habits or exercise comes from within – teens included. In other words, if your teen wants to work on this, she will because she is motivated to do so.

Being told what to do, or what to eat may fall on deaf ears, or be met with resentment or resistance. Be ‘chill’ with your teen on the topics of weight and exercise, but be ready and open to help when you’re called to do so.

Have you had an experience with this? How did you handle it?

What if Your Teen Has Unexplained Weight Gain?

Usually, weight gain in teens is a gradual process, but sometimes, a teen may have what appears to be sudden weight gain. This may be due to lifestyle choices, but sometimes lifestyle is in a good place and the weight keeps piling on.

You may need to further investigate medical causes of sudden weight gain.

Talk with your family doctor regarding additional testing to rule out or uncover a medical condition that may be responsible for your teen’s weight gain.

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This post was updated on September 12, 2020.

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