Causes and Risk Factors of Obesity

Reviewed by: HU Medical Review Board | Last reviewed: May 2023

Obesity is a complex condition that has become a major public health concern around the world. In the United States alone, nearly 1 in 4 adults live with obesity. There are many different causes and risk factors of obesity, which adds to its complexity.1,2

Obesity can lead to several chronic diseases. These include heart disease, diabetes, and certain types of cancer. Knowing the causes and risk factors of obesity is crucial to preventing and managing it and other conditions.1

How is obesity measured?

One way obesity is measured is by calculating a person’s body mass index (BMI). This is a measurement of body fat based on a person’s height and weight. A BMI of 30 or above is considered obese.1,3

That said, BMI is not the only tool that healthcare providers use to determine whether a person has obesity. Many other factors come into play.1

What are the causes and risk factors of obesity?

There are many causes and risk factors of obesity, including:1,3

  • Calories in versus calories out
  • Genetics
  • Lifestyle and diet
  • Medical conditions and treatments
  • Environmental factors

Calories in versus calories out

One of the main causes of obesity is an imbalance between calories consumed and calories burned. The body burns calories by carrying out bodily functions and physical movement. When a person eats or drinks (consumes) more calories than they burn throughout the day, the excess calories are stored as fat. This can lead to weight gain over time.1,3


Genetics also play a role in the development of obesity. Certain genetic conditions can affect metabolism, the body’s process of changing food into energy. A slow metabolism can make it harder for some people to maintain a healthy weight.1,3

People with a family history of obesity are more likely to develop the condition themselves. But genetics is not the only determinant of obesity. Lifestyle factors, like diet and exercise, also play a big role.1,3

Lifestyle and diet

A sedentary lifestyle can play a huge role in a person’s weight. In the modern world, many people spend long hours sitting at a desk or in front of a screen, with little to no physical activity. This is known as a sedentary lifestyle. It can lead to a decreased number of calories burned and an increased risk of weight gain.3

Be sure you are getting regular physical activity throughout your day. This will look different for different people based on their level of ability. If you sit at a desk to work, consider getting up every hour to move around or stretch. You can take the stairs rather than the elevator if you are able. Even small changes can make a big difference.1,3

Diet is also extremely important. Consuming a diet high in calories, saturated fats, and added sugars can lead to weight gain. Processed foods and fast foods are often high in calories and low in nutritional value. This makes them a major contributor to obesity.3

Try to eat a diet rich in whole, unprocessed foods, including fruits, vegetables, lean proteins, and healthy fats. This can help prevent weight gain and improve your overall health.3

Medical conditions and treatments

Certain medical conditions also can contribute to obesity. Hypothyroidism, Cushing's syndrome, and polycystic ovary syndrome (PCOS) are examples of conditions that can cause weight gain.1,3,4

Weight gain is also a common side effect of some medicines, such as antidepressants. If you are taking medicine and have noticed an increase in your weight, tell your doctor about your concerns. There may be a different drug you can switch to.1,3

Environmental factors

Sometimes, there are factors in your environment that are out of your control. For example, you may live in a neighborhood with limited access to healthy food options. You may not have safe places to go for exercise. These factors can make it harder to maintain a healthy weight.1,3

Other risk factors

There are still other factors that can increase a person's chances of developing obesity. These include:3,5

  • Older age – Hormone changes and mobility issues can affect weight.
  • Increased stress – Turning to food during times of stress is a common coping mechanism that may lead to weight gain.
  • Pregnancy – Many find the added weight from pregnancy is hard to lose after the baby is born.
  • Sleep problems – Studies show that poor sleep changes hormone levels and metabolism, which can affect weight.

Know your risk for obesity

Obesity is a complex condition that is affected by a variety of factors. Knowing these risk factors can help you prevent or manage obesity. Maintain a healthy diet, get regular exercise, and reduce sedentary behavior as best you can. These can help prevent obesity.1,3

Talk with your doctor about your risk factors and any concerns you may have about your overall health. They can help you make a plan to prevent unhealthy weight gain or pursue weight loss in a safe way for your body.1,3

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