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About obesity

More about obesity: Definition, symptoms and diagnosis

Obesity is a chronic disease that can seriously impact your quality of life and wellbeing. Here’s everything you need to know about obesity - including symptoms, diagnosis, and an accurate obesity definition.

4 min. read

Obesity definition

Obesity is defined as a chronic disease characterized by an excess amount of body fat.

Obesity has been linked to other major chronic diseases such as heart disease, cancer, stroke, and diabetes. It can also be a serious condition in its own right. In most groups of people, a BMI equal to or more than 25 kg/m² represents an increased risk and requires additional evaluation. A BMI equal to or more than 30 kg/m² is associated with increased cardiovascular risk factors and mortality, so it should be used to screen for obesity.

One of the ways to classify obesity is by using the Body Mass Index (BMI). This is a calculation that takes your height and body weight into account. BMI is calculated by dividing weight in kilograms by the square of height in meters. 

BMI is used to measure body fat and is an objective way to classify underweight, overweight, and obesity in adults. If your BMI is equal to or more than 30kg/m² you may be diagnosed as a person with obesity. Within the official obesity definition, there are different classifications of the disease.

BMI Classification Underweight - Below 18.5 kg/m²  
  Normal - 18.5–24.9 kg/m²  
  Overweight - 25.0–29.9 kg/m²  
  Obesity Class I - 30.0-34.9 kg/m²  
  Obesity Class II - 35.0–39.9 kg/m²  
  Obesity Class III - Above 40 kg/m²  


These classifications are a standardised measurement and form part of an internationally recognised obesity definition. 

What are the symptoms of obesity?

In addition to a BMI greater than 30 kg/m², there are also other symptoms associated with obesity that can impact your ability to do certain activities. Here are some symptoms of obesity that you might notice in your day-to-day life:

  • Difficulty doing physical activity like climbing stairs
  • Breathlessness
  • Increased sweating
  • Snoring
  • Feeling tired regularly
  • Joint pain
  • Back pain
  • Low confidence and self-esteem
  • Feeling isolated
  • Depression, anxiety, and mood disorders

If you're experiencing any of these symptoms of obesity, it's a good idea to talk to your doctor.

Getting a formal obesity diagnosis

A formal obesity diagnosis may be an important step in treating and managing obesity and losing weight.

However, few patients get a formal obesity diagnosis and this can lead to barriers in getting the help you need. Research shows that only 55% of patients with BMI of 30 or above received a formal obesity diagnosis.

This may be because many doctors feel uncomfortable talking about obesity with their patients. It's important that you raise the issue with your doctor to begin moving forward with treating or managing obesity.

You can also find obesity care providers who are trained in obesity management to help make the process easier. They might do several things to make an obesity diagnosis, including asking questions about your medical history, a physical examination, and laboratory assessment.

The process might involve some or all of these steps.

Questions about your lifestyle and medical history

To make an obesity diagnosis, your doctor might ask you some questions about your lifestyle, medical history, and family history.

This includes questions related to your:

  • Ethnicity
  • Family history
  • Diet
  • Physical activity and exercise habits
  • Eating disorders
  • Depression and other mood disorders
  • Genetics
  • Drugs
  • Chronic stress
  • Smoking habits

These are all factors that are related to obesity and can be used to understand possible causes of obesity.

A physical exam

In addition to questions and discussing possible causes of obesity, your doctor may also give you a physical exam to help them identify any symptoms of obesity.

This might include:

  • Measuring weight, height, and waist circumference
  • Measuring blood pressure
  • Assessing if you have obesity-related diseases (for example, diabetes, hypertension, respiratory disease, and others)
  • Looking for acanthosis nigricans (dry, dark patches of skin that can be a sign of insulin resistance)

The results of your physical exam can help your doctor make an accurate obesity diagnosis based on the symptoms of obesity.

Laboratory tests

Your doctor may also want to do laboratory tests to identify any underlying symptoms of obesity.

Laboratory tests can be used to find out:

  • Fasting blood glucose
  • Serum lipid profile (including total, HDL and LDL cholesterol, triglycerides)
  • Uric acid
  • Thyroid function (thyroid-stimulating hormone (TSH) level)
  • Liver function (hepatic enzymes)
  • Cardiovascular assessment
  • Endocrine evaluation
  • Liver investigation (including ultrasound or biopsy)
  • NAFLD or other liver pathology
  • Sleep laboratory investigation for sleep apnoea.

Your doctor will select which laboratory tests to run depending on your specific case and can give you more information during your consultation.

Expectations and treatment options

Your doctor might also want to talk to you about your expectations and treatment options for managing symptoms of obesity. 

This might include questions about how willing you are to manage weight, any previous treatments for the symptoms of obesity, and information on the benefits of weight loss.

They might also outline the health consequences of obesity and potential complications associated with the disease.

If you show that you’re motivated to manage weight, your doctor might talk about introducing a diet plan and exercise program tailored to your needs. 

What are the causes of obesity?

The cause of obesity is complex and linked to many different factors

Obesity develops when the amount of calories you take in is higher than the amount of energy you expend. But, there is also growing evidence that obesity is caused by inherited traits that affect the mechanisms which regulate weight in the body.

In recent years, the official obesity definition has changed. Health professionals now understand that the disease is influenced by a complex mix of genetic, environmental, and behavioral factors that contribute to symptoms of obesity.

What is an accurate obesity definition?

People can have different ideas about what is considered an accurate obesity definition.  

To understand if you are living with obesity and get a formal obesity diagnosis, it is important to talk to your doctor. They will be able to advise you on healthy ways to manage your weight and the symptoms of obesity.

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Find your local obesity care provider

Talk to your obesity care provider about treatment options that could prevent the weight you lose from coming back.

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