When children eat more than they need, their bodies store the extra calories in fat cells to use for energy later. If their bodies do not need this stored energy, they develop more fat cells and may become overweight or develop obesity.

No single factor or behavior causes obesity. Obesity is caused by many things, including a person's habits, lifestyle, and environment. Genes and some medical problems also increase a person's chances of developing obesity.

Overweight in children - causes and risks

Infants and young children are very good at listening to their bodies' signals of hunger and fullness. They will stop eating as soon as their bodies tell them they have had enough. But sometimes a well-meaning parent tells them they have to finish everything on their plate. This forces them to ignore their fullness and eat everything that is served to them.

The way we eat when we are children may strongly affect our eating behaviors as adults. When we repeat these behaviors over many years, they become habits. They affect what we eat, when we eat, and how much we eat.

Other learned behaviors include using food to:

• Reward good behaviors
• Seek comfort when we feel sad
• Express love

These learned habits lead to eating no matter if we are hungry or full. Many people have a very hard time breaking these habits.

The family, friends, schools, and community resources in a child's environment reinforce lifestyle habits regarding diet and activity.

Children are surrounded by many things that make it easy to overeat and harder to be active:

• Parents have less time to plan and prepare healthy meals. As a result, children are eating more processed and fast foods that are usually less healthy than home-cooked meals.
• Children see up to 10,000 food commercials every year. Many of these are for fast food, candy, soft drinks, and sugared cereals.
• More foods today are processed and high in fat and contain too much sugar.
• Vending machines and convenience stores make it easy to get a quick snack, but they rarely sell healthy foods.
• Overeating is a habit that is reinforced by restaurants that advertise high-calorie foods and large portion sizes.

If a parent is overweight and has poor diet and exercise habits, the child is likely to adopt the same habits.

Screen time, such as watching television, gaming, texting, and playing on the computer are activities that require very little energy. They take up a lot of time and replace physical activity. And, when children watch TV, they often crave the unhealthy high-calorie snacks they see on commercials.

Schools have an important role in teaching students about healthy food choices and exercise. Many schools now limit unhealthy foods in lunches and vending machines. They are also encouraging students to exercise more.

Having a safe community that supports outdoor activities at parks, or indoor activities at community centers, is important for encouraging physical activity. If a parent feels it is not safe to allow their child to play outside, the child is more likely to do sedentary activities inside.

The term eating disorders refers to a group of medical problems that have an unhealthy focus on eating, dieting, losing or gaining weight, and body image. Examples of eating disorders are:

• Anorexia
• Bulimia

Obesity and eating disorders often occur at the same time in teens and young adults who may be unhappy with their body image.

Some children are at greater risk for obesity because of genetic factors. They have inherited genes from their parents that make their bodies gain weight easily. This would have been a very good trait hundreds of years ago, when food was hard to find and people were very active. Today, though, this can work against people who have these genes.

Genetics is not the only cause of obesity. To develop obesity, children must also eat more calories than they need for growth and energy.

Obesity may be linked to rare genetic conditions, such as Prader-Willi syndrome. Prader-Willi syndrome is a disease that is present from birth (congenital). It is the most common genetic cause of severe and life threatening childhood obesity.

Certain medical conditions can increase a child's appetite. These include hormone disorders or low thyroid function, and certain medicines, such as steroids or anti-seizure medicines. Over time, any of these can increase the risk for obesity.

Centers for Disease Control and Prevention website. Childhood obesity facts. www.cdc.gov/obesity/php/data-research/childhood-obesity-facts.html. Updated April 2, 2024. Accessed June 25, 2024.

Gahagan S. Overweight and obesity. In: Kliegman RM, St. Geme JW, Blum NJ, Shah SS, Tasker RC, Wilson KM, eds. Nelson Textbook of Pediatrics. 21st ed. Philadelphia, PA: Elsevier; 2020:chap 60.

O'Connor EA, Evans CV, Burda BU, Walsh ES, Eder M, Lozano P. Screening for obesity and intervention for weight management in children and adolescents: evidence report and systematic review for the US Preventive Services Task Force. JAMA. 2017;317(23):2427-2444. PMID: 28632873 pubmed.ncbi.nlm.nih.gov/28632873/.