Obesity means having too much body fat. It is different from being overweight, which means weighing too much. The weight may come from muscle, bone, fat, and/or body water. Both terms mean that a person’s weight is greater than what’s considered healthy for his or her height.
The US obesity prevalence was 42.4% in 2017 – 2018. The estimated annual medical cost of obesity in the United States was $147 billion in 2008, according to the CDC. Medical costs for people who had obesity were $1,429 higher than medical costs for people with a healthy weight.
Additionally, Non-Hispanic Black adults (49.6%) had the highest age-adjusted prevalence of obesity.
Obesity happens over time after continuously eating more calories than you use. This causes your body to store the calories as fats. The balance between calories in and calories out differs for each person. Factors that might affect your weight include your genetic makeup, overeating, eating high-fat foods, and not being physically active.
According to the CDC, in the United States, most people’s diets are too high in calories — often from fast food and high-calorie beverages. People with obesity might eat more calories before feeling full, feel hungry sooner, or eat more due to stress or anxiety.
Many people also have jobs that are much less physically demanding, so they don’t tend to burn as many calories at work. Even daily activities use fewer calories, due to the convenience of remote controls, escalators, online shopping and drive-through banks.
Obesity usually results from a combination of causes and contributing factors:
Family inheritance and influences
The genes you inherit from your parents may affect the amount of body fat you store, and where that fat is being distributed. Genetics may also play a role in how efficiently your body converts food into energy, how your body regulates your appetite and how your body burns calories during exercise.
Obesity tends to run in families. That’s not just because of the genes they share. It’s because family members also tend to share similar eating and activity habits.
- Unhealthy diet. A diet that’s high in calories, lacking in fruits and vegetables, full of fast food, and laden with high-calorie beverages and oversized portions contributes to weight gain.
- Liquid calories. People can drink many calories without feeling full, especially calories from alcohol. Other high-calorie beverages, such as sugary soft drinks, can contribute to significant weight gain.
- Inactivity. If you have a sedentary lifestyle, you can easily take in more calories every day than you burn through exercise and routine daily activities. Looking at computer, tablet and phone screens is a sedentary activity. The number of hours spent in front of a screen is highly associated with weight gain.
Certain diseases and medications
In some people, medical conditions can be the cause of their obesity. These conditions include Prader-Willi syndrome, Cushing syndrome and other conditions. Medical problems, such as arthritis, can also lead to decreased activity, which may result in weight gain.
Some medications can also cause you to gain weight if you don’t compensate through diet or activity. These medications include some antidepressants, anti-seizure medications, diabetes medications, antipsychotic medications, steroids and beta blockers.
Social and economic issues
Social and economic factors are also linked to obesity. Avoiding obesity may be more difficult if you don’t have safe areas to walk or exercise. Similarly, you may not have been taught healthy ways of cooking, or you may not have access to healthier foods. In addition, the people you spend time with may have a negative influence on your weight making you more likely to develop obesity if you have friends or relatives with obesity.
Obesity can occur at any age, even in young children. But as you age, hormonal changes and a less active lifestyle can increase your risk of obesity. In addition, the amount of muscle in your body tends to decrease with age. Generally, lower muscle mass leads to a decrease in metabolism. These changes also reduce calorie needs and can make it harder to keep off excess weight. If you don’t consciously control what you eat and become more physically active as you age, you’ll likely gain weight.
- Pregnancy. Weight gain is common during pregnancy. Some women may find it difficult to lose weight after the baby is born. This weight gain may contribute to the development of obesity in women.
- Quitting smoking. Quitting smoking is often associated with weight gain. And for some, it can lead to enough weight gain to qualify as obesity. Many people use food to cope with smoking withdrawal. In the long run, however, quitting smoking is still a greater benefit to your health than continuing to smoke. If you are having trouble, your doctor can help you prevent weight gain after quitting smoking.
- Lack of sleep. Not getting enough sleep or getting too much sleep can cause changes in hormones that increase appetite. You may also crave foods high in calories and carbohydrates, which can contribute to weight gain.
- Stress. Many external factors that affect mood and well-being may contribute to obesity. People often seek more high-calorie food when experiencing stressful situations.
- Microbiome. Your gut bacteria are affected by what you eat and may contribute to weight gain or difficulty losing weight.
Even if you have one or more of these risk factors, it doesn’t mean that you’re destined to develop obesity.
If you have obesity, losing even 5 to 10% of your weight can delay or prevent some of the diseases that obesity causes. For example, that means a person that weighs 200 pounds would lose 10 to 20 pounds.
People with obesity are more likely to develop a number of potentially serious health problems, including:
- Heart disease and strokes. Obesity makes you more likely to have high blood pressure and abnormal cholesterol levels, which are risk factors for heart disease and strokes.
- Type 2 diabetes. Obesity can affect the way the body uses insulin to control blood sugar levels. This raises the risk of insulin resistance and diabetes.
- Certain cancers. Obesity may increase the risk of cancer of the uterus, cervix, endometrium, ovary, breast, colon, rectum, esophagus, liver, gallbladder, pancreas, kidney and prostate.
- Digestive problems. Obesity increases the likelihood of developing heartburn, gallbladder disease and liver problems.
- Sleep apnea. People with obesity are more likely to have sleep apnea, a potentially serious disorder in which breathing repeatedly stops and starts during sleep.
- Osteoarthritis. Obesity increases the stress placed on weight-bearing joints, in addition to promoting inflammation within the body. These factors may lead to complications such as osteoarthritis.
- Severe COVID-19 symptoms. Obesity increases the risk of developing severe symptoms if you become infected with the virus that causes coronavirus disease (COVID-19). People who have severe cases of COVID-19 may require treatment in intensive care units or even mechanical assistance to breathe.
Quality of life
Obesity can also diminish your overall quality of life meaning you may not be able to do the physical activities that you once enjoyed. This may cause you to avoid public places. People with obesity are also subjected to discrimination.
Other weight-related issues that may affect your quality of life include:
- Shame and guilt
- Social isolation
- Lower work achievement
Body mass index (BMI) is often used to diagnose obesity. To calculate your BMI, multiply your weight in pounds by 703, divide by height in inches and then divide again by height in inches. Or divide your weight in kilograms by height in meters squared.
For most people, BMI provides a reasonable estimate of body fat. However, BMI doesn’t directly measure body fat, so some people, such as muscular athletes, may have a BMI in the obesity category even though they don’t have excess body fat.
Many doctors also measure a person’s waist circumference to help guide treatment decisions. Weight-related health problems are more common in men with a waist circumference over 40 inches (102 centimeters) and in women with a waist measurement over 35 inches (89 centimeters).
You can counteract most risk factors through diet, physical activity and exercise, and behavior changes.