Doctors use the medical terms "overweight" or "obese" to tell if someone has a greater chance of developing weight-related health problems.

How Are Overweight and Obesity Defined?

Body mass index (BMI) uses height and weight measurements to estimate a person's body fat. But calculating BMI on your own can be complicated. An easier way is to use a BMI calculator.

After calculating BMI and plotting the result on standard BMI charts, doctors use four categories to describe weight in kids ages 2 to 19:

• underweight: BMI below the 5th percentile
• normal weight: BMI at the 5th and less than the 85th percentile
• overweight: BMI at the 85th and below 95th percentiles
• obese: BMI at or above 95th percentile

For kids younger than 2 years old, doctors use weight-for-length charts instead of BMI to determine how a baby's weight compares with their length. A child under 2 who falls at or above the 95th percentile is considered overweight.

BMI is not a perfect measure of body fat and can be misleading in some cases. For example, a muscular person may have a high BMI without being overweight (extra muscle adds to body weight — but not fatness). Also, BMI might be hard to interpret during puberty when kids have periods of fast growth. Remember, BMI is usually a good indicator of body fat, but it's not a direct measurement.

If you're worried about your child’s weight, take them to see the doctor. The doctor will ask about eating and activity habits and make suggestions on how to make healthy lifestyle changes. The doctor also may order blood tests to look for some of the medical problems linked to obesity.

Depending on your child's BMI (or weight-for-length measurement) and health, the doctor may refer you to a registered dietitian or a weight management program. Doctors also can prescribe medicine or surgery for some kids.

Why Do Kids Become Overweight or Obese?

Things that can contribute to a person becoming overweight included poor diet habits, not enough exercise, genetics, or a combination of these. Lack of access to healthy food and safe places to be active is a challenge for many families. Rarely, too much weight gain may be due to an endocrine problem, genetic syndrome, or some medicines.

Diet and Lifestyle

We often choose foods that are quick and easy to eat — from fast food to processed and prepackaged meals and snacks. Busy schedules can leave little time to make healthier meals or to squeeze in some exercise. Portion sizes, at home and away, are too large.

Plus, modern life is sedentary. Kids often spend more time playing with electronic devices than actively playing outside. Kids who spend a lot of time in front of screens are more likely to be overweight. Screen time also interferes with sleep. Kids who don’t get enough sleep are more likely to be overweight.

Exercise and Physical Activity

Many kids don't get enough physical activity. Older kids and teens should get 1 hour or more of moderate to vigorous exercise every day, including and muscle- and bone-strengthening activities. Kids ages 2 to 5 years should be active at least 3 hours throughout each day.

Genetics

Genetics can play a role in what kids weigh. Our genes help determine body type and how the body stores and burns fat. But genes alone can't explain the current obesity crisis. Because both genes and habits are passed down from one generation to the next, multiple members of a family may struggle with weight.

People in the same family tend to have similar eating patterns, sedentary behaviors, and levels of physical activity. A child's chances of being overweight increase if a parent is overweight or obese.

What Health Problems Can Being Overweight Cause?

People with high BMI are more likely to have weight-related health problems. These include type 2 diabetes, high blood pressure, and high cholesterol — all of which used to be considered adult diseases.

Overweight kids and teens may also have:

• bone and joint problems
• shortness of breath that makes exercise, sports, or any physical activity harder. It also can make asthma symptoms worse or lead kids to develop asthma.
• restless sleep or breathing problems at night, such as obstructive sleep apnea
• a tendency to mature earlier. Overweight kids may be taller and more sexually mature than their peers, raising expectations that they should act as old as they look, not as old as they are.
• irregular menstrual cycles and fertility problems in adulthood
• liver and gallbladder disease

Cardiovascular risk factors (including high blood pressure, high cholesterol, and diabetes) that develop in childhood can lead to heart disease and stroke in adulthood. Preventing or treating overweight and obesity in kids may help protect them from these problems as they get older.

Kids also might have emotional issues to deal with (such as low self-esteem), and may be teased, bullied, or rejected by peers. Kids who are unhappy with their weight can be at risk for:

• unhealthy dieting and eating disorders
• depression
• substance abuse

How Can We Prevent Overweight and Obesity?

Preventing kids from becoming overweight means making choices about how your family eats, exercises, and spends time together. Helping kids adopt a healthy lifestyle begins with parents who lead by example.

To keep kids of all ages at a healthy weight, take a whole-family approach. Make healthy eating and exercise a family affair. Get your kids involved by letting them help you plan and prepare healthy meals. Take them along when you go grocery shopping. Teach them how to make good food choices.

Try to avoid these common traps:

• Don't reward kids for good behavior or try to stop bad behavior with sweets or treats. Talk to your doctor about other ways to change behavior.
• Don't have a clean-plate policy. Even babies turn away from the bottle or breast to send signals that they're full. If kids are satisfied, don't force them to keep eating. Reinforce the idea that they should eat only when they're hungry and stop when they're full.
• Don't talk about "bad foods" or completely ban all sweets and favorite snacks. Kids may rebel and overeat forbidden foods outside the home or sneak them in on their own. Serve healthy foods most of the time and offer treats once in a while.

Recommendations by Age

Other recommendations for kids of all ages:

• Birth to age 1: Besides its many health benefits, breastfeeding may help prevent excessive weight gain. Follow your doctor’s recommendations about when to introduce solid foods.
• Ages 1 to 5: Start good habits early. Help shape food preferences by offering a variety of healthy foods. Encourage kids' natural tendency to be active and help them build on developing skills.
• Ages 6 to 12: Encourage kids to be physically active every day, whether through an organized sports team or being active during recess. Keep your kids active at home with everyday activities like playing outside or going for a family walk. Teach them to make good food choices and get them involved in preparing food, such as packing lunch.
• Ages 13 to 18: Teach teens how to prepare healthy meals and snacks at home. Encourage them to make healthy choices when outside the home and to be active every day.
• All ages: Cut down on TV, phone, computer, and video game time and discourage eating in front of a screen (TV or otherwise). Serve a variety of healthy foods and eat family meals together as often as possible. Encourage kids to eat breakfast every day; have at least 5 servings of fruits and vegetables daily; and limit sugar-sweetened beverages, like soda, juice, and sports drinks. Make sure they get enough sleep.

Talk to kids about the importance of eating well and being active. Be a role model by eating well, exercising regularly, and building healthy habits into your own daily life. Make it a family affair, and a healthy lifestyle will be second nature for everyone.