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Overview of Obesity

Facts about obesity

Overweight and obesity together make up one of the leading preventable causes of death in the U.S. Obesity is a chronic disease that can seriously affect your health.  

Overweight means that you have extra body weight, and obesity means having a high amount of extra body fat. Being overweight or obese raises your risk for health problems. These include coronary heart disease, type 2 diabetes, asthma, high cholesterol, osteoarthritis, high blood pressure, sleep apnea, and certain types of cancer.

Public health experts agree that overweight and obesity have reached epidemic proportions in this country and around the world. More than a third of U.S. adults are obese. People ages 60 and older are more likely to be obese than younger adults, according to the most recent data from the National Health and Nutrition Examination Survey. And the problem also affects children. Approximately 20%, of U.S. children and teens ages 2 to 19 are obese.

Who's obese?

View of a man's belly as he sits on a park bench, wearing a yellow shirt

Overweight and obesity are different points on a scale that ranges from being underweight to being morbidly obese. Where you fit on this scale is determined by your body mass index (BMI).

BMI is a measure of your weight as it relates to your height. BMI usually gives you a good idea of the amount of body fat you have. Your healthcare providers use BMI to find out your risk for obesity-related diseases. Occasionally, some very muscular people may have a BMI in the overweight range. But these people are not considered overweight because muscle tissue weighs more than fat tissue.

In general, a BMI from 20 to 24.9 in adults is considered ideal. A BMI of more than 25 is considered overweight. A person is considered obese if the BMI is greater than 30 and is considered to have morbid obesity if the BMI is 40 or greater.

In general, after the age of 50, a man's weight tends to stay the same and often decreases slightly between ages 60 and 74. In contrast, a woman's weight tends to increase until age 60, and then begins to decrease.

Obesity can also be measured by waist-to-hip ratio. This is a measurement tool that looks at the amount of fat on your waist, compared with the amount of fat on your hips and buttocks. The waist circumference tells the amount of stomach fat. Increased stomach fat is associated with type 2 diabetes, high cholesterol, high blood pressure, and heart disease. A waist circumference of more than 40 inches in men and more than 35 inches in women may increase the risk for heart disease and other diseases tied to being overweight.

Talk with your healthcare provider if you have questions about healthy body weight.

What causes obesity?

In many ways, obesity is a puzzling disease. Experts don't know exactly how your body regulates your weight and body fat. What they do know is that a person who eats more calories than he or she uses for energy each day will gain weight.

But the risk factors that determine obesity can be complex. They are usually a combination of your genes, socioeconomic factors, metabolism, and lifestyle choices. Some endocrine disorders, diseases, and medicines may also affect a person's weight.

Factors that may affect obesity include the following.


Studies show that the likelihood of becoming obese is passed down through a family's genes. Researchers have found several genes that appear to be linked with obesity. Genes, for instance, may affect where you store extra fat in your body. But most researchers think that it takes more than just one gene to cause an obesity epidemic. They are continuing to do more research to better understand how genes and lifestyle interact to cause obesity. Because families eat meals together and share other activities, environment and lifestyle also play a role.

Metabolism factors

How your body uses energy is different from how another person's uses it. Metabolism and hormones differ from person to person, and these factors play a role in how much weight you gain. One example is ghrelin, the "hunger hormone" that regulates appetite. Researchers have found that ghrelin may help trigger hunger. Another hormone called leptin can decrease appetite. Another example is polycystic ovary syndrome (PCOS), a condition in women caused by high levels of certain hormones. A woman with PCOS is more likely to be obese.

Socioeconomic factors

How much money you make may affect whether you are obese. This is especially true for women. Women who are poor and of lower social status are more likely to be obese than women of higher socioeconomic status. This is especially true among minority groups.

Lifestyle choices

Overeating and a lack of exercise both contribute to obesity. But you can change these lifestyle choices. If many of your calories come from refined foods or foods high in sugar or fat, you will likely gain weight. If you don't get much if any exercise, you'll find it hard to lose weight or maintain a healthy weight.


Medicines like corticosteroids, antidepressants, and antiseizure medicines can cause you to gain some extra weight.


Emotional eating–eating when you're bored or upset–can lead to weight gain. Too little sleep may also contribute to weight gain. People who sleep fewer than 5 hours a night are more likely to become obese than people who get 7 to 8 hours of sleep a night.

Health effects of obesity

Obesity has a far-ranging negative effect on health. Each year in the U.S., obesity-related conditions cost more than $ 150 billion and cause premature deaths. The health effects linked with obesity include:

High blood pressure

Excess weight needs more blood to circulate to the fat tissue and causes the blood vessels to become narrow (coronary artery disease). This makes the heart work harder, because it must pump more blood against more resistance from the blood vessels and can lead to a heart attack (myocardial infarction). More circulating blood and more resistance also means more pressure on the artery walls. Higher pressure on the artery walls increases the blood pressure. Excess weight also raises blood cholesterol and triglyceride levels and lowers HDL ("good") cholesterol levels, adding to the risk of heart disease.

Type 2 diabetes

Obesity is the major cause of type 2 diabetes. Obesity can make your body resistant to insulin, the hormone that regulates blood sugar. When obesity causes insulin resistance, your blood sugar level rises. Even moderate obesity dramatically increases the risk for diabetes.

Heart disease

Atherosclerosis, or hardening of the arteries, happens more often in obese people. Coronary artery disease is also more common in obese people because fatty deposits build up in arteries that supply the heart. Narrowed arteries and reduced blood flow to the heart can cause chest pain called angina or a heart attack. Blood clots can also form in narrowed arteries and travel to the brain, causing a stroke.

Joint problems, including osteoarthritis

Obesity can affect the knees and hips because extra weight stresses the joints. Joint replacement surgery may not be a good choice for an obese person because the artificial joint has a higher risk of loosening and causing more damage.

Sleep apnea and respiratory problems are also related to obesity

Sleep apnea causes people to stop breathing for brief periods during sleep. Sleep apnea interrupts sleep and causes sleepiness during the day. It also causes heavy snoring. Sleep apnea is also linked to high blood pressure. Breathing problems tied to obesity happen when added weight of the chest wall squeezes the lungs. This restricts breathing.


Being overweight or obese increases your risk for a variety of cancers, according to the American Cancer Society. Among obese women, the risk increases for cancer of the endometrium or the lining of the uterus in younger women. Obese women also increase their risk for breast cancers in those who have gone through menopause. Men who are overweight have a higher risk for prostate cancer. Both men and women who are obese are at increased risk for colorectal cancer.

Metabolic syndrome

The National Cholesterol Education Program says that metabolic syndrome is a risk factor for cardiovascular disease. Metabolic syndrome has several major risk factors. These are stomach obesity, high blood triglyceride levels, low HDL cholesterol levels, high blood pressure, and insulin resistance (severe type 2 diabetes). Having at least three of these risk factors confirms the diagnosis of metabolic syndrome. 

Psychosocial effects

People who are overweight or obese can have problems socially or psychologically. This is because the culture in the U.S. often values a body image that's overly thin. Overweight and obese people are often blamed for their condition. Other people may think of them as lazy or weak-willed. It's not uncommon for people who are overweight or obese to earn less than other people or to have fewer or no romantic relationships. Some people's disapproval and bias against of those who are overweight may progress to discrimination, and even torment. Depression and anxiety are more common in people who are overweight and obese. 

Online Medical Reviewer: Jonas DeMuro MD
Online Medical Reviewer: Raymond Kent Turley BSN MSN RN
Online Medical Reviewer: Rita Sather RN
Date Last Reviewed: 10/1/2020
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