Obesity is defined in the Canadian Adult Obesity Clinical Practice Guidelines as a complex and progressive disease where excess or abnormal body fat impairs health. Obesity can lead to increased risk of long-term health complications and shortened lifespan.

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 metres. In most people, a BMI of 25 kg/m² or more represents an increased risk of obesity affecting your health and requires additional evaluation. While BMI alone cannot be used to diagnose obesity, a BMI of 30 kg/m² or more is associated with increased cardiovascular risk and mortality, and anyone looking for more support with their obesity should consult their healthcare practitioner.

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.

Cut-offs are different for people of South-, Southeast- or East Asian descent.

Remember, these classifications are part of an international standardized measurement and cannot predict how obesity will impact your health. 

There are many symptoms of obesity that can impact your day-to-day life. Obesity symptoms may include:

• Difficulty doing physical activity like climbing stairs
• Breathlessness
• Sleep disturbances
• Feeling tired regularly
• Joint pain
• Back pain
• Low confidence and self-esteem
• Personality changes
• Depression, anxiety, and mood disorders

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

Diagnosing obesity is an important first step in treating and managing your weight.

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

During an assessment, a healthcare provider may ask questions related to:

• Ethnicity
• Family history
• Eating patterns/commercial weight loss programs
• 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.

This may include:

• Measuring weight, height, and waist circumference
• Measuring blood pressure
• Assessing if you have obesity-related diseases (for example, osteoarthritis, gout, 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 which laboratory tests to run depending on your assessment.

Laboratory tests may be used to assess:

• Fasting blood glucose (to measure your sugar levels when they are at their lowest) or HbA1C 
• Cholesterol levels (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 health (to assess your hormone levels)
• Metabolic dysfunction-associated steatotic liver disease (MASLD) using ultrasound, biopsy, or other liver tests 
• Cardiovascular health
• The presence of sleep apnea (when your breathing stops and starts in your sleep) at a sleep laboratory

If you live with obesity or are overweight, you may have experienced weight bias or had stigmatized conversations with a healthcare professional in the past. This is because obesity as a disease is a relatively new area of 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 that obesity is becoming a priority for healthcare teams all over the world. In fact, some countries now have specialized weight management clinics for treating obesity.