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 CDC, “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.
What are the symptoms of obesity?
There are no specific symptoms associated with obesity. A doctor may diagnose obesity based on the following factors:
excess amounts of abdominal (visceral) fat that are higher than the amounts of body fat in other areas
a waist circumference of greater than 40 inches for men or 35 inches for women
a BMI over 30
How is obesity classified?
The following classes are used for adults who are at least 20 years old:
How is obesity classified?
The following classesTrusted Source are used for adults who are at least 20 years old:
What causes obesity?
Taking in more calories than you burn in daily activity and exercise — on a long-term basis — can lead to obesity. Over time, these extra calories add up and cause weight gain.
But it’s not always just about calories in and calories out or having a sedentary lifestyle. While those are indeed causes of obesity, some causes you can’t control.
Common specific causes of obesity include:
genetics, which can affect how your body processes food into energy and how fat is stored
growing older, which can lead to less muscle mass and a slower metabolic rate, making it easier to gain weight
not sleeping enough, which can lead to hormonal changes that make you feel hungrier and crave certain high calorie foods
high stress, which may trigger the production of hormones that cause you to eat more and store more fat
pregnancy, as weight gained during pregnancy may be difficult to lose and might eventually lead to obesity
Certain health conditions can also lead to weight gain, which may lead to obesity. These include:
metabolic syndrome, a group of risk factors that include high blood pressure, high blood sugar, high levels of triglycerides, low levels of HDL cholesterol, and excess fat around your waist that raise your chance of developing certain serious health conditions
polycystic ovary syndrome (PCOS), a condition that causes an imbalance of hormones called androgens.
Prader-Willi syndrome, a rare condition present at birth that causes excessive hunger
Cushing syndrome, a condition caused by having high levels of cortisol (the stress hormone) in your system
hypothyroidism (underactive thyroid), a condition in which the thyroid gland doesn’t produce enough of certain important hormones
osteoarthritis (OA) and other conditions that cause pain that may lead to reduced activity
Who is at risk of obesity?
A complex mix of factors can increase a person’s risk of obesity.
Genetics
Some people have genes that make it more likely for them to gain weight and body fat.
Environment and community
Your environment at home, at school, and in your community can all influence how and what you eat, as well as how active you are.
You may be at a higher risk of developing obesity if you:
live in a neighborhood with limited nutritious food options or with manyTrusted Source high calorie food options, like fast-food restaurants
haven’t learned to cook balanced meals
think you can’t afford more nutritious foods
haven’t found a good place to play, walk, or exercise in your neighborhood
Psychological and other factors
Depression can sometimes lead to weight gain, as some people may turn to food for emotional comfort.
Having disturbed sleeping patterns can make you eat more during the day, especially foods high in fat and carbohydrates.
If you smoke, quitting smoking is beneficial to your health, but quitting may lead to weight gain too. In some people, it may lead to excessiveTrusted Source weight gain. For that reason, it’s important to focus on diet and exercise while you’re quitting, at least after the initial withdrawal period.
Medications
Certain medications can also raise your risk of weight gain. These medications can include:
corticosteroids, which may treat autoimmune disease
antidepressants
antipsychotics
beta-blockers, which may treat high blood pressure
How is obesity diagnosed?
BMI provides a rough calculation of a person’s weight in relation to their height.
Other more accurate measures of body fat and where body fat is located include:
skinfold thickness tests
waist-to-hip comparisons
dual energy radiographic absorptiometry (DEXA) scans
other screening tests, such as ultrasounds, CT scans, and MRI scans
A doctor may also order certain tests to help diagnose obesity-related health risks. These may include:
blood tests to examine cholesterol and glucose levels
liver function tests
diabetes screening
thyroid tests
heart tests, such as an electrocardiogram (ECG or EKG)
How is obesity diagnosed?
BMI provides a rough calculation of a person’s weight in relation to their height.
Other more accurate measures of body fat and where body fat is located include:
skinfold thickness tests
waist-to-hip comparisons
dual energy radiographic absorptiometry (DEXA) scans
other screening tests, such as ultrasounds, CT scans, and MRI scans
A doctor may also order certain tests to help diagnose obesity-related health risks. These may include:
blood tests to examine cholesterol and glucose levels
liver function tests
diabetes screening
thyroid tests
heart tests, such as an electrocardiogram (ECG or EKG)
