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The Basics of Obesity

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

Obesity is a very serious health issue in the United States and around the world. About 93 million Americans currently live with obesity, including both adults and children. And experts expect that number to continue to rise in the future. In fact, a global study predicts that about 1 in 4 people will live with obesity by the year 2035.1,2

With so many people affected by this condition, it is important to understand the basics of obesity and weight loss. When you understand obesity and how to address it, you can begin to work toward a healthy weight and improve your health.

What is obesity?

Obesity is a condition in which a person has an unhealthy amount of body fat. When their proportion of body fat is too high, it can lead to a number of health problems. Obesity can be caused by genetics as well as environmental and lifestyle factors.3

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There are several ways to diagnose obesity. One common way is to measure a person’s body mass index (BMI). BMI takes into account the person's height and weight.3

  • A BMI of 18.5 to 24.9 is considered healthy.
  • A BMI of 25.0 to 29.9 is considered overweight.
  • A BMI of 30 or above is considered obese.

While BMI is a tool that can provide helpful information, it is only one part of the obesity equation. There are many other factors that should be considered when diagnosing obesity.3

What causes obesity?

Obesity can be a complex condition with many different causes. One of the main causes of obesity is an imbalance between calories consumed and calories burned.2

When a person eats or drinks (consumes) more calories than they burn, the extra calories are stored in the body as fat. This can happen when a person consumes too much food, consumes unhealthy foods or drinks, or does not get enough physical activity.2

But there also may be other factors at play that can cause obesity, such as:3

  • Genetics
  • Hormonal imbalances
  • Depression or stress
  • Socioeconomic factors (for example, having limited access to fresh, healthy foods due to income level or location)
  • Medicines that can cause weight gain

What are the complications of obesity?

If left untreated, obesity may lead to a variety of health problems, including:4

  • Joint issues
  • Heart disease
  • Type 2 diabetes
  • High blood pressure
  • High cholesterol
  • Gallbladder disease
  • Sleep apnea
  • Stroke
  • Some types of cancer

How can weight loss help people with obesity?

If you are living with obesity, losing weight can offer a variety of health benefits. Even a small amount of weight loss can lead to great health rewards, such as:2,3

  • Improved blood pressure, cholesterol, and blood sugars
  • Less joint pain
  • Improved sleep apnea
  • Better overall quality of life

Is weight loss right for you?

Not everyone with obesity will develop these health problems. But being aware of these complications is important. Talk with your doctor if you are living with obesity and are concerned about developing any of these conditions. They may recommend a weight loss strategy that incorporates different tactics to get you to a healthy weight.3,4