What is childhood obesity?

Childhood obesity is a body weight that is greater than that considered healthy for a child's height. Carrying excess body fat can have a range of serious consequences for children's health, particularly in their future.

In the United States, the percentage of children and adolescents affected by obesity has more than tripled since the 1970s. Data from 2015-2016 show that nearly 1 in 5 school age children and young people (6 to 19 years) in the United States has obesity.

Obesity is defined as having excess body fat. Body mass index (BMI) is a widely used screening tool for measuring obesity. BMI is a person's weight in kilograms divided by the square of a person's height in meters. Scientists have found that BMI is moderately related to direct measures of body fatness. Measuring height and weight is easier and less expensive than other methods for assessing weight status.

The US Centers for Disease Control and Prevention (CDC) recommends that health professionals use BMI percentile when measuring the bodies of children and young people aged 2 to 20 years. BMI percentile takes into account that young people are still growing and are growing at different rates depending on their age and sex. Health professionals use growth charts to determine whether a young person's weight falls into a healthy range for his or her height, age, and sex.

Measurement of overweight and obesity

Because carrying excess weight can affect many aspects of your health, your doctor may ask to weigh and measure your child and discuss their weight at regular visits.

There are a number of measures that can be applied to determine whether a child's weight may cause health problems. These include:

  • Body mass index (percentile charts) for children aged 2-18 years of age, and;
  • World Health Organization (WHO) growth charts for babies and infants up to two years of age.

Waist circumference, which is commonly used to estimate abdominal fat and therefore assess overweight or obesity in adults, is not used in the same way in children. Your doctor may measure the waist circumference of your child in order to monitor changes in growth, but it does not indicate a potential health risk from carrying extra abdominal weight.

Body mass index 

Body mass index (BMI) is a tool that is used to classify the weight of adults into healthy, overweight and obese. It is recommended by the WHO and used as the main measurement in many guidelines for obesity around the world.

BMI is calculated by dividing the weight (in kilograms) by height (in meters) squared. In children, BMI is assessed in conjunction with percentile charts that take into account your child's gender and age. This is because weight and growth varies as children develop.

There are two different BMI percentile charts that may be used to assess a child as overweight or obese:

  • WHO percentile charts, and;
  • US-CDC percentile charts.

Chart

Percentile Range

Weight range

WHO

85-97

Overweight

 

≥98

Obesity

US-CDC

85-95

Overweight

 

≥96

Obesity

The type of chart that is used to assess your child does not matter greatly, but if your child is assessed by different doctors who use different charts, the results might vary slightly. It is also important to remember that the BMI is an approximate guide and is not accurate for everyone.

One reason for this is that people with the same weight can carry different amounts of fat compared to their lean body mass (bone and muscle). 

Also, BMI does not take into account where body fat is accumulated on the body. Not all body fat contributes equally to health problems. Fat underneath the skin, particularly on the hips and thighs does not tend to cause as many problems as fat around your abdomen. In particular, fat that builds up around the organs inside the abdominal cavity can cause inflammation within the body and contribute to many of the health problems associated with obesity.

At any given weight, different people will carry varying amounts of fat around their abdomen. The greater the amount of abdominal fat, the higher the risk of health problems.

In assessing the potential risk that extra weight can pose to your child, your doctor, in addition to estimating the BMI, will also take into account many other lifestyle and health aspects. 

Causes

Consuming more energy from foods and beverages than the body uses for healthy functioning, growth, and physical activity can lead to extra weight gain over time. The Dietary Guidelines for Americans encourage children and adolescents to maintain calorie balance to support normal growth and development without promoting excess weight gain. Energy imbalance is a key factor behind the high rates of obesity seen in the United States and globally.

Many factors contribute to childhood obesity, including:

  • Genetics
  • Metabolism--how your body changes food and oxygen into energy it can use.
  • Community and neighborhood design and safety.
  • Short sleep duration.
  • Eating and physical activity behaviors.

Genetic factors are difficult to change. However, people and places can play a role in helping children achieve and maintain a healthy weight. Families, communities, schools, out-of-school programs, medical care providers, faith-based institutions, government agencies, the media, food and beverage companies, and entertainment industries all influence the dietary and physical activity behaviors of children and adolescents.

Changes in the environments where young people spend their time--like homes, schools, and community settings--can make it easier to achieve and maintain a healthy weight. Schools can adopt policies and practices that help young people eat more fruits and vegetables, get at least 60 minutes of physical activity daily, and eat fewer foods and beverages that are high in added sugars or solid fats.

In some respects the cause of obesity is quite simple - it occurs because your child takes in more energy through food and drink than their body uses, so the excess energy gets converted into fat.

Energy in

Energy in food is measured in kilojoules or calories (1 calorie = 4.2 kilojoules). Foods vary in the amount of energy they provide. For example, vegetables tend to be low in energy and high in fiber and nutrients that the body requires. Foods that contain a lot of carbohydrates and fats tend to be high in energy, and not necessarily high in fiber and nutrients.

Beverages also contribute to energy intake. While water contains no energy, soft drinks and fruit juices are high in energy. The portion size of the foods your child eats is also important. Even foods with moderate amounts of energy can contribute to weight gain if they are eaten to excess.

Energy out

Metabolism describes the chemical processes that occur inside the cells in the body in order for the body to function. These processes require energy - this is called basal metabolism.

Physical activity also uses up energy. The more vigorous the exercise (such as running), the more energy the body will use, although all activities - such as playing, walking to the shops and even standing still - contribute to the amount of energy the body uses every day.

With high-energy foods, your child can take in large amounts of energy very quickly, while it takes much more time and effort to work off that energy.

Control of body weight

Taking in small amounts of extra energy on a daily basis can eventually add up to carrying quite a lot of extra weight if your child does it over a long period of time.

However, the way the body regulates weight is more complex. It involves a system of hormones in the body (including insulin, leptin and ghrelin) that:

  • Increase hunger;
  • Decrease appetite and food intake, and;
  • Increase metabolism and the amount of energy the body expends.

Generally speaking, this system works to try to maintain body weight in a healthy range over time. Although as children grow, it is normal at various stages of their development for weight and amount of body fat they carry to change.

Medical conditions that can contribute to weight gain

There are some medical conditions that can contribute to weight gain and make it harder to lose weight.

They include:

Some medications can also contribute to weight gain.

Growth hormone deficiency

A condition in children in which the pituitary gland does not produce enough growth hormone. This can affect a child’s growth.

Insulin

A hormone secreted by the pancreas in order to regulate glucose levels in the body's cells, which is used for energy.

Prader-Willi syndrome

A rare genetic disorder that affects development and growth, typically causing poor muscle tone, short stature, incomplete sexual development, cognitive disabilities, problem behaviors and obsessive eating.

Leptin

A chemical produced by the fatty tissue that signals to the brain feelings of fullness.

Ghrelin

A chemical produced by stomach cells that signals to the brain feelings of hunger.

Cushing's syndrome

A group of disorders characterized by high levels of cortisol, an important chemical in the body with numerous functions including stress responses, maintaining blood sugar levels and helping the immune system.

Risk factors

Beyond the personal choices about what foods your child eats and how physically active they are, there are many factors that can affect their weight.

Risk factors include:

Genetics

Evidence suggests that the genes a child inherits from their parents strongly affect their weight.

Epigenetics

Epigenetics describes how genes can be turned on and off (a process called gene expression) without the genes themselves being changed. It is thought some epigenetic changes may play a significant role in controlling body weight.

Early life

Factors in early life, such as the nutrition of the mother during pregnancy, low or high birth weights and the amount of weight gained during the first few months of life can affect body weight later in life.

Environment

Environment affects the way people behave. Factors that contribute to weight gain are sometimes called 'obesogenic' and research into how they contribute to weight gain in the community is ongoing. These factors can include the kinds of foods that are easily available, neighborhood design and infrastructure that makes physical activity difficult or unsafe, sedentary activities such as spending a lot of time in front of the TV or computer, and poor-quality or disrupted sleep (which can affect metabolism and hormones that control appetite).

Psychological factors

Stress has been linked to increased eating and a lack of energy, which can reduce the motivation to be physically active. Mental health issues and obesity are strongly linked. For example, people with depression are more likely to become obese and people who are obese are more likely to become depressed.

Health consequences of being overweight or obese

Carrying extra weight has a range of consequences for the body. Not only can it increase levels of inflammation in the body and affect the body's metabolic processes, it also places extra load and stress on important structures such as the joints, the airways and the bladder.

Health risks that are increased in childhood by carrying extra weight include:

A child who is overweight or obese is more likely to carry extra weight as an adult. As well as the risks above, as an adult they can also be at greater risk of developing:

Carrying very large amounts of extra weight can also make it more difficult for doctors to treat a wide range of other health problems. For example, surgery can be more complicated and it can take longer to recover.

Anxiety

A feeling of tension, nervousness and dread about future events. It can trigger physical symptoms such as a rapid pulse or breathing difficulties.

Endometrial

Relating to the internal lining of the uterus.

Gall bladder

A small organ attached to the liver that stores bile until it is released into the small intestine, to aid the digestion of food.

Incontinence

The uncontrollable loss, small or large, of bladder or bowel control, resulting in leakage of their contents.

Insulin

A hormone secreted by the pancreas in order to regulate glucose levels in the body's cells, which is used for energy.

Stroke

A disruption in the oxygen supply to the blood, due to an artery leading to the brain becoming blocked or ruptured.

Esophageal

Pertaining to the esophagus, the muscular tube connecting the throat and stomach. Also known as the food pipe.

Pancreatic

Relating to the pancreas, an organ located in the abdomen that secretes important chemicals, such as insulin, into the bloodstream and digestive enzymes into the intestines.

Types of treatment

For most children, weight loss is not recommended as an approach to deal with overweight and obesity. Rather, the focus is on maintaining weight so that as the child grows, their BMI will steadily decrease.

For children who are very obese, and particularly where there are signs of other health problems or mental health issues that may be contributing to weight gain, your doctor may recommend a referral to a pediatrician or a psychologist specializing in treating children and adolescents.

Recommended approaches to weight loss include:

  • Reducing energy intake via a healthy eating plan, and; 
  • Increasing a child's physical activity levels to increase their energy output.

For children, the family environment is particularly important. Parents and caregivers are responsible for providing nutritious food and opportunities to be physically active and also serve as role models for the kinds of behaviors that are key to being a healthy weight. Getting the whole family involved can help children achieve a healthier weight.

For adolescents who are very obese, options such as medication to assist weight loss (orlistat) and bariatric surgery (also known as obesity surgery) may be considered if they:

  • Have not been able to prevent weight gain despite trying lifestyle changes, and/or;
  • Have related health problems such as diabetes.

Your doctor can discuss whether these options are suitable for your child.

A boy being physically active by playing football. 

Prognosis

Being overweight or obese increases your child's risk of a range of serious health conditions and can be linked with reduced life expectancy. However, making lifestyle changes that help to reduce weight gain and help your child achieve a healthy weight can help to reduce these risks.

Prevention

It is easier to prevent weight gain than to try and lose excess weight. The same lifestyle changes that can help to lose weight can also help to prevent weight gain.

Further references

Obesity Facts | Healthy Schools | CDC