What Is Obesity?

Obesity is a serious, chronic disease that can have a negative effect on many systems in your body. People who are overweight or obese have a much greater risk of developing serious conditions, including:

• Heart disease
• Type 2 diabetes
• Bone and joint disease

Obesity in the United States

The U.S. Surgeon General has declared that obesity has reached epidemic proportions in the United States. Approximately:

• 35 percent of women and 31 percent of men are considered seriously overweight
• 15 percent of children between the ages of six and 19 are overweight

Public health officials warn that the results of physical inactivity and poor diet are catching up to tobacco as a significant threat to health. We are committed to helping you get healthy and stay that way. Learn about obesity prevention.

Causes of Obesity

The causes of obesity are complex. There are many interrelated factors, such as genetics, lifestyle and how your body uses energy. Learn more about the causes of obesity and risk factors.

Body Mass Index (BMI) Calculator

Take the first step to managing your weight from the comfort of your home. Use our BMI calculator to help you determine whether or not you are considered obese. If you are obese, or have one or more risk factors for obesity, our physicians can help. In cases of severe obesity, surgery may be an option. Learn more about obesity treatments at Stanford.

Health Effects of Obesity

Obesity has a far-ranging negative effect on health. Each year obesity-related conditions cost over 150 billion dollars and cause an estimated 300,000 premature deaths in the US. The health effects associated with obesity include, but are not limited to, the following:

• High blood pressure - Additional fat tissue in the body needs oxygen and nutrients in order to live, which requires the blood vessels to circulate more blood to the fat tissue. This increases the workload of the heart because it must pump more blood through additional blood vessels. More circulating blood also means more pressure on the artery walls. Higher pressure on the artery walls increases the blood pressure. In addition, extra weight can raise the heart rate and reduce the body's ability to transport blood through the vessels.
• Diabetes - Obesity is the major cause of type 2 diabetes. This type of diabetes usually begins in adulthood but, is now actually occurring in children. Obesity can cause resistance to insulin, the hormone that regulates blood sugar. When obesity causes insulin resistance, the blood sugar becomes elevated. Even moderate obesity dramatically increases the risk of diabetes.
• Heart disease – Atherosclerosis (hardening of the arteries) is present 10 times more often in obese people compared to those who are not obese. Coronary artery disease is also more prevalent because fatty deposits build up in arteries that supply the heart. Narrowed arteries and reduced blood flow to the heart can cause chest pain (angina) or a heart attack. Blood clots can also form in narrowed arteries and cause a stroke.
• Joint problems, including osteoarthritis - Obesity can affect the knees and hips because of the stress placed on the joints by extra weight. Joint replacement surgery, while commonly performed on damaged joints, may not be an advisable option for an obese person because the artificial joint has a higher risk of loosening and causing further damage.
• Sleep apnea and respiratory problems - Sleep apnea, which causes people to stop breathing for brief periods, interrupts sleep throughout the night and causes sleepiness during the day. It also causes heavy snoring. Respiratory problems associated with obesity occur when added weight of the chest wall squeezes the lungs and causes restricted breathing. Sleep apnea is also associated with high blood pressure.
• Cancer - In women, being overweight contributes to an increased risk for a variety of cancers including breast cancer, colon, gallbladder, and uterus. Men who are overweight have a higher risk of colon cancer and prostate cancers.
• Metabolic syndrome - The National Cholesterol Education Program has identified metabolic syndrome as a complex risk factor for cardiovascular disease. Metabolic syndrome consists of six major components: abdominal obesity, elevated blood cholesterol, elevated blood pressure, insulin resistance with or without glucose intolerance, elevation of certain blood components that indicate inflammation, and elevation of certain clotting factors in the blood. In the US, approximately one-third of overweight or obese persons exhibit metabolic syndrome.
• Psychosocial effects - In a culture where often the ideal of physical attractiveness is to be overly thin, people who are overweight or obese frequently suffer disadvantages. Overweight and obese persons are often blamed for their condition and may be considered to be lazy or weak-willed. It is not uncommon for overweight or obese conditions to result in persons having lower incomes or having fewer or no romantic relationships. Disapproval of overweight persons expressed by some individuals may progress to bias, discrimination, and even torment.