Obesity and Overweight

Overweight and obesity are diseases in which a person’s weight, given their height, is too high and can cause health problems. Obesity carries greater health risks than having overweight.

NICHD is one of many federal agencies and NIH institutes working to understand overweight and obesity. NICHD supports and conducts research on the causes of excess weight, how to prevent and treat obesity, and related topics, including conditions caused by having obesity.

About Obesity and Overweight

Weight that is higher than what is considered healthy, based on a person’s height, is called “overweight” or “obesity.”  A person with obesity has too much body fat. A person with overweight weighs too much, but the extra weight may come from muscle, bone, body water, and/or fat.1

Healthcare providers often use body mass index (BMI) to determine if a person is affected by overweight or obesity. Adults who have a BMI between 25 and 29.9 are generally considered to be affected by overweight. Adults who have a BMI of 30 or higher are considered to be affected by obesity.2 A child’s weight status is determined using a special chart that takes into account the child’s age and sex.3Learn more about BMI and other measurements of overweight and obesity.

Obesity is a chronic disease. Being affected by obesity increases a person’s risk for health conditions, such as diabetes, cardiovascular disease, bone and joint problems, and circulatory issues, to name a few.

The U.S. Centers for Disease Control and Prevention gathers and reports statistics on obesity and overweight in adults and children at https://www.cdc.gov/obesity/data/index.html.


  1. National Library of Medicine. (2012). Obesity. Retrieved 2021, from MedlinePlus: http://www.nlm.nih.gov/medlineplus/obesity.html
  2. Centers for Disease Control and Prevention. (2012). Overweight and obesity: Defining overweight and obesity. Retrieved 2021, from http://www.cdc.gov/obesity/adult/defining.html
  3. Centers for Disease Control and Prevention. (2012). Overweight and obesity: Basics about childhood obesity. Retrieved August 8, 2012, from https://www.cdc.gov/obesity/childhood/defining.html

How are obesity & overweight diagnosed?

Using Body Mass Index (BMI)

The most common way to determine if a person is affected by overweight or obesity is to calculate BMI, which  is an estimate of body fat that compares a person’s weight to their height.

Healthcare providers use BMI, along with information about additional risk factors, to determine a person’s risk for developing weight-related diseases. Usually, the higher a person’s BMI, the higher the risk of disease.

BMI for Adults

An adult’s BMI can be determined using a BMI calculator. Healthcare providers use BMI ranges to indicate a person's weight status. For adults, a BMI of:

  • 18.5 to 24.9 is considered normal weight
  • 25.0 to 29.9 is considered overweight
  • 30.0 to 39.9 is considered obesity
  • 40.0 and higher is considered extreme obesity1

It is important to remember that although BMI is generally a good way to estimate how much body fat a person has, it does not measure body fat directly and therefore is not reliable in all cases. For example, a person may have extra weight because he or she is athletic and has a lot of muscle, and not because he or she has excess body fat.

BMI for Children and Teens

For children age 2 and older and for teens, BMI uses weight and height, but adds sex and age into the calculation. Instead of using a specific number like the BMI charts for adults, the BMI for children and teens is listed as a percent. This percentage indicates a child’s BMI in relation to the BMIs of other children of the same sex and age. A child and teen BMI calculator can provide a BMI.

Children age 2 and older are considered to have:

  • A healthy weight if their BMI falls between the 5th and the 85th percentiles
  • Overweight if their BMI is between the 85th and 95th percentiles
  • Obesity if their BMI is at or higher than the 95th percentile2

Other Ways to Measure Body Fat

Body fat can be measured in other ways than BMI, including waist circumference, calculation of waist-to-hip circumference ratios, measuring the thickness of a skinfold (a pinch of skin and fat), and techniques such as ultrasound that are more precise than BMI. A healthcare provider can help determine if such tests are necessary.


  1. National Heart, Lung, and Blood Institute. (2012). How are overweight and obesity diagnosed? Retrieved August 8, 2012, from https://www.nhlbi.nih.gov/health/educational/lose_wt/risk.htm
  2. Barlow, S. E., & the Expert Committee. (2007). Expert committee recommendations regarding the prevention, assessment, and treatment of child and adolescent overweight and obesity: Summary report. Pediatrics, 120, S164–S192.

What are the treatments for obesity & overweight?

To maintain a healthy weight, it is important to create a balance between the calories taken in and the calories used. To lose weight, a person usually needs to reduce calories and increase physical activity.

If lifestyle changes are not enough to reduce weight, medicines and weight-loss surgery may also be options for some people.1

What are some tips for healthy eating?

  • Emphasize fruits, vegetables, whole grains, and fat-free or low-fat milk and dairy products.
  • Include lean meats, poultry, fish, beans, eggs, and nuts.
  • Eat a diet low in saturated fats, trans fats, cholesterol, salt (sodium), and added sugars.
  • Drink more water instead of sugary drinks.

How much physical activity does an adult need?

Getting enough physical activity is an important way to help prevent or reduce the risk of overweight and obesity and related health problems.

  • Adults age 18 and older need at least 30 minutes of physical activity on 5 or more days of the week to be healthy.
  • Children and teens need at least 60 minutes of activity a day for their health.

Learn more about weight-loss techniques, medications, and surgery options.


  1. National Heart, Lung, and Blood Institute. (2012). How are overweight and obesity treated? Retrieved August 8, 2012, from https://www.nhlbi.nih.gov/health-topics/overweight-and-obesity

What causes obesity & overweight?

Several factors can play a role in gaining and retaining excess weight. These include diet, lack of exercise, environmental factors, and genetics. Some of these factors are discussed briefly in the following section. The National Heart, Lung, and Blood Institute offers more information on the causes of overweight and obesity.

Food and Activity

People gain weight when they eat more calories than they burn through activity. This imbalance is the greatest contributor to weight gain.


The world around us influences our ability to maintain a healthy weight. For example:

  • Not having area parks, sidewalks, and affordable gyms makes it hard for people to be physically active.
  • Oversized food portions increase Americans’ calorie intake, making even more physical activity necessary to maintain a healthy weight.
  • Some people don’t have access to supermarkets that sell affordable healthy foods, such as fresh fruits and vegetables.
  • Food advertising encourages people to buy unhealthy foods, such as high-fat snacks and sugary drinks.1


Research shows that genetics plays a role in obesity. Genes can directly cause obesity in such disorders as Prader-Willi syndrome.

Genes also may contribute to a person’s susceptibility to weight gain. Scientists believe that genes may increase a person’s likelihood of having obesity but that outside factors, such as an abundant food supply or little physical activity, also may be required for a person to have excess weight.2

Health Conditions and Medications

Some hormone problems may cause overweight and obesity, such as underactive thyroid, Cushing syndrome and polycystic ovary syndrome.

Certain medicines also may cause weight gain, including some corticosteroids, antidepressants, and seizure medicines.1

Stress, Emotional Factors, and Poor Sleep

Some people eat more than usual when they are bored, angry, upset, or stressed.

Studies also have found that the less people sleep, the more likely they are to have overweight or obesity. This is partly because hormones that are released during sleep help control appetite and the body’s use of energy.1


  1. National Heart, Lung, and Blood Institute. (2012). What causes overweight and obesity? Retrieved August 8, 2012, from https://www.nhlbi.nih.gov/health-topics/overweight-and-obesity
  2. Centers for Disease Control and Prevention. (2012). Overweight and obesity: Causes and consequences. Retrieved August 8, 2012, from https://www.cdc.gov/obesity/basics/causes.html
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