Obesity is defined by medical professionals as a complex and progressive disease where excess or abnormal body fat causes and increases the risk of long-term health complications.

The most common way to classify obesity is by using the Body Mass Index (BMI) - a measure calculated by dividing weight in kilograms by the square of height in meters. In most people, a BMI of 25 kg/m² or more represents an increased risk of obesity and overweight symptoms and requires additional evaluation. While BMI does not qualify an obesity diagnosis, a BMI of 30 kg/m² or more is associated with increased cardiovascular risk and mortality, and anyone with a BMI of 30 or above should consult their doctor for support.

BMI is an objective way to classify underweight, normal weight, overweight, and obesity in adults. Within the official obesity definition, there are different classifications of the disease.

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

In addition to a BMI of 30 kg/m² or more, there are other symptoms of obesity that can impact your day-to-day life.  Obesity symptoms may include:

• 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, it's a good idea to speak to a healthcare professional.
 

An obesity diagnosis may be an important step in treating and managing obesity the condition.

Diagnosing obesity usually involves an assessment of lifestyle, medical and family history, a physical examination and/or laboratory tests.

To assess lifestyle, medical and family history, a healthcare provider may ask 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

A physical examination may also be necessary to support a formal diagnosis of obesity. Guidelines recommend healthcare professionals carry out an Edmonton Obesity Staging System (EOSS), which is a measure of the mental, metabolic and physical impact of obesity. This can then help your healthcare professionals find the right treatment plan for you.  

This may include:

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

Lastly, laboratory tests may be administered to identify the underlying signs and symptoms of obesity. Your healthcare professional will select what laboratory tests to run depending on your case and assessment needs. 

Laboratory tests may be used to assess:

• Fasting blood glucose (to measure your sugar levels when they are at their lowest)
• Cholesterol test (including total, HDL and LDL cholesterol, triglycerides)
• Uric acid (a normal waste product that passes through your kidneys and leaves your body in urine)
• Thyroid function and endocrine evaluation (to assess your hormone levels)
• Liver function
• Liver investigation (including ultrasound or biopsy)
• Non-alcoholic fatty liver disease (NAFLD) or other liver pathology
• Cardiovascular assessment
• Sleep laboratory investigation for sleep apnoea (when your breathing stops and starts in your sleep)

If you live with overweight or obesity, you may have experienced weight-bias or had stigmatised conversations with a doctor or healthcare provider in the past. This is because obesity as a disease is a relatively new area for scientific research and development. This has led to a long period of misunderstanding by society and healthcare professionals alike. The important thing to remember is there is a lot of progress being made to make the treatment of obesity a priority for healthcare teams all over the world. In fact, some countries now have specialised weight management clinics for treating overweight and obesity.