Obesity is a long-term (chronic) health condition that progresses over time. Obesity is defined by excess body fat (adipose tissue) that may impair health.

Body mass index (BMI) is a calculation that takes a person’s weight and height into account to measure body size. Doctors typically use it as a screening tool for obesity.

In adults, obesity is often defined as having a BMI of 30 or moreTrusted Source

, according to the Centers for Disease Control and Prevention (CDC). Obesity is associated with a higher risk of developing serious diseases, including:

• type 2 diabetes
• heart disease
• cancer

While BMI tends to relate to the level of body fat, it has some limitations as a measurement.

According to the CDCTrusted Source

, “Factors such as age, sex, ethnicity, and muscle mass can influence the relationship between BMI and body fat. Also, BMI doesn’t distinguish between excess fat, muscle, or bone mass, nor does it provide any indication of the distribution of fat among individuals.”

Despite these limitations, BMI continues to be widely used as a way to measure body size. This is because it’s less expensive than other methods.

It’s worth noting that the effects of weight discrimination can also contribute to negative health effects.

Obesity is common. The CDC estimates that 41.9%Trusted Source

 of people in the United States had obesity from 2017 to March 2020.

Keep reading to learn more about obesity causes, risk factors, and treatment.