Obesity is a disease in which a person has an excess amount of body fat. Learn about obesity, including its causes and signs, and how to keep a healthy weight.

What is Obesity?

Obesity is disease in which a person has an excess amount of body fat. Research has shown that extra fat in the body produces several chemicals that can cause serious diseases. This can include diabetes, high blood pressure, high cholesterol, liver problems and a condition called polycystic ovary syndrome in females (where females make higher than typical amounts of male hormones).

How Common is Obesity?

Obesity is one of the most common chronic (long-term) diseases that affects all ages. One out of every 3 children ages 10-17 years has overweight or obesity.

What Causes Weight Gain?

Everyone has a set target for how much fat their body needs – called the fat mass goal. The fat mass goal is determined by a variety of factors like genetics, age, race/ethnicity and the environment. This fat mass goal changes to a higher level in some situations, like after eating a high fat diet for a long time or due to some medications.

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Rev. 3/2020/ MassGeneral Hospital for Children and Massachusetts General Hospital do not endorse any of the brands listed on this handout. This handout is intended to provide health information so that you can be better informed. It is not a substitute for medical advice and should not be used to treatment of any medical conditions.