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Last Updated: Mar 1, 2019


An obese person has more body fat than what is considered normal for his or her height. Although sometimes used interchangeably, the term “overweight” refers to increased body weight from fat, muscle, bone and fluids, while “obese” only refers to excess fat.

Obesity, which is the disease of carrying excess fat, affects one third of Americans (about 78.6 million) and is a leading cause of mortality and soaring healthcare costs in the country. This is because obesity increases the risk of developing a myriad of chronic diseases including heart disease, high cholesterol, hypertension, liver disease, type 2 diabetes, respiratory disorders, sexual dysfunction, osteoarthritis and some cancers. Additionally, obese people are more likely to suffer from depression, social isolation and physical limitations.

Obesity is the result of an imbalance between calorie intake and calorie expenditure. Genetics, a high-calorie diet and low physical activity are all contributors to a buildup of body fat. Dietary and lifestyle trends that cause obesity are showing global impact, with both adulthood and childhood obesity on the rise around the world. Over the last 30 years in the United States, the numbers of obese children in the 6-11 and 12-19 age groups have more than doubled and quadrupled, respectively.

With lifestyle changes and medication, it is possible to achieve a healthy weight and avoid secondary diseases; even modest weight loss can delay or prevent associated complications. Surgical procedures that force a limit on the amount of food intake or slow fat absorption are also available.

Causes and Risk Factors

The body stores excess fat as a result of too much caloric intake and a lack of calorie expenditure through physical activity. Poor diet and inactivity are often influenced by environmental factors like community behavior and socioeconomics. Genetics and other health conditions may also play a role. Known causes and risk factors for obesity include:

  • Poor diet. An unbalanced diet with few fruits/vegetables and a disproportionally high amount of fat and added sugars (such as from fast foods and sodas) - consuming more calories than what the body needs, and choosing nutrient-poor foods rather than nutritious foods - causes weight gain.
  • Sedentary lifestyle. Regular physical activity burns calories gained through diet. Poor health, disability, occupation or other conditions that bring about prolonged inactivity cause obesity.
  • Family. Children with obese parents are more likely to become obese themselves because they generally adopt a similar diet and lifestyle.
  • Socioeconomics. Easy access to outdoor space and healthy foods can greatly influence the overall health of a community. Cities with sidewalks and public transportation encourage walking or biking, which help burn calories. Importantly, low-income families are more likely to choose low-cost fast foods that are rich in calories.
  • Genetics. Evidence suggests that genes may play a role in hunger, fat storage and calorie expenditure in some obese individuals.
  • Illness. Some medical conditions like Prader-Willi syndrome and Cushing’s syndrome are linked to obesity.
  • Medication. Steroid and beta blocker drugs and some medications used for treating depression, diabetes and seizures can cause excess weight gain.
  • Pregnancy. Pregnant women who necessarily gain weight during pregnancy, but then have trouble losing the weight or continue to gain weight post-pregnancy, are at risk of becoming obese.
  • Age. The risk of obesity grows with age due to inactivity and decreased muscle mass, both of which lead to weight gain.


The symptoms of obesity include:

  • High body mass index (BMI)
  • An expanding waistline
  • Gaining weight
  • Switching to larger sized clothing.

Diagnosis and Treatment

Doctors diagnose obesity by performing a general exam and learning about the patient’s personal/family medical history. The body mass index (BMI) and waist circumference are routinely used to estimate “fatness”. The BMI is calculated by dividing a person’s weight (kilograms) by the square of their height (meters); it is solely an estimate and not a direct measurement for body fat. The BMI is associated with weight in the following way:

  • BMI is below 18.5 = Underweight
  • BMI is 18.5-24.9 = Normal weight
  • BMI is 25.0-29.9 = Overweight
  • BMI is 30.0 or more = Obese.

Excess abdominal fat is also reflected in the waist circumference. The risk of obesity and related complications increases when the waist circumference measures over 35 inches for women, and over 40 inches in men.

Obesity is treated by achieving and maintaining a healthy weight through a combination of diet, exercise, medication and, in some cases, surgery. At-risk or obese children are encouraged to eat healthy and increase physical activity. Obese adults are advised to lose 5-10 percent of their body weight as an initial step in a comprehensive treatment plan that includes:

  • Dietary changes. Choosing healthy foods and reducing caloric intake are key to losing weight. The ideal diet is low in cholesterol and saturated fats, and includes fruits, vegetables, whole grains and lean meats. The recommended number of daily food calories varies for each person but is roughly 1,000-1,200 calories per day for women, and 1,200-1,600 calories per day for men.
  • Physical activity. Doing 150-300 minutes of moderate to intense exercise per week will help remove excess weight and maintain a healthy weight. Simple changes in habit that encourage more movement (e.g. gardening) also help burn calories.
  • Behavior changes. It is important to identify and manage the triggers of hunger or unnecessary snacking. Counseling and support groups can facilitate this process and help patients manage their food cravings.
  • Medication. Obese patients who cannot reduce their weight with diet and exercise alone are candidates for prescription drugs that curb hunger or reduce fat absorption.
  • Surgery. Extremely obese patients or those with serious weight-related complications may consider weight-lost surgery. Although surgery offers excellent results with respect to weight loss and maintenance, it carries important risks. Surgical procedures work by either reducing the stomach’s holding capacity (gastric banding, gastric sleeve), reducing fat absorption through the small intestine (biliopancreatic diversion with duodenal switch), or both (gastric bypass).


The best way to maintain a healthy weight is through regular exercise and a balanced diet that is low in saturated fats and added sugars. It is also important to address medical or environmental factors that trigger hunger and inactivity.


  • “Obesity”. The Obesity Society. Retrieved Jul 15, 2015.
  • “Obesity”. Mayo Clinic. Mayo Foundation for Medical Education and Research. Retrieved Jul 15, 2015.
  • “Obesity”. National Institutes of Health. NIH. Retrieved Jul 15, 2015.

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Tina Shahian, PhD

Tina is a writer for Innerbody Research, where she has written a large body of informative guides about health conditions.


A communication specialist in life science and biotech subjects, Tina’s successful career is rooted in her ability to convey complex scientific topics to diverse audiences. Tina earned her PhD in Biochemistry from the University of California, San Francisco and her BS degree in Cell Biology from U.C. Davis. Tina Shahian’s Linkedin profile.


In her spare time, Tina enjoys drawing science-related cartoons.