Skip to contentSkip to navigation

Neat Little Guide — 15 minutes

What is obesity and what are the risks?

Obesity: Definition, Diagnosis and Causes

child's feet on a scale

According to the World Health Organization (WHO), overweight and obesity are characterized by “abnormal or excessive fat accumulation that may impair health.”

The WHO says that globally:

  • Obesity has nearly tripled since 1975.
  • In 2016, more than 1.9 billion adults, 18 years and older, were overweight. Of these, over 650 million were obese.
  • 39% of adults aged 18 years and over were overweight in 2016, and 13% were obese.
  • Most of the world's population lives in countries where overweight and obesity kill more people than underweight.
  • In 2016, 41 million children under the age of 5 were overweight or obese.
  • In 2016, over 340 million children and adolescents aged 5-19 were overweight or obese.
  • Closer to home, Statistics Canada indicates that in 2018, 36.3% of Canadians aged 18 or older were overweight and 26.8% (25% of Quebecers) were obese. Therefore, more than 63% of the Canadian population is at risk of health problems associated with overweight and obesity.

But how do you judge whether you are overweight or obese? To help you find out, you can consult Health Canada’s Canadian Guidelines for Body Weight Classification in Adults, which are based on WHO recommendations. To estimate adult overweight and obesity, the guidelines use the Body Mass Index (BMI), a simple measure of your weight relative to your height (your weight divided by the square of your height, expressed in kg/m2).

Click here to access the BMI calculator on the Centers for Disease Control and Prevention website.

Health Canada recommends not to use an online calculator to assess overweight or obesity if you are under the age of 18, pregnant or breastfeeding. Other factors should be taken into account if you are naturally very thin, have strong muscles, have not stopped growing or are over the age of 65.

Health Canada classifies health risks based on BMI as follows:

Classification BMI category Risk of developing health problems
Insufficient weight < 18.5 Higher
Normal weight 18.5 to 24.9 Less
Excess weight 25.0 to 29.9 Higher
Obesity, Class I 30.0 to 34.9 Elevated
Obesity, Class II 35.0 to 39.9 Very high
Obesity, Class III > 40.0 Extremely high

Other factors are also taken into consideration, in addition to BMI, including the waist circumference, which makes it possible to determine excess abdominal fat (this is referred to as abdominal obesity when the waist is more than 88 cm in women and 102 cm in men) and the waist to hip circumference ratio which provides an even more precise picture of the distribution of fat in the body (the ratio is considered elevated when the result is higher than 1 in men and higher than 0.85 in women).

Causes and risk factors

Obesity is a chronic, complex and evolving disease that depends on a combination of physical activity, diet, socio-economic status, ethnicity, environment and food marketing, genetic predisposition and depression.

When you burn fewer calories than you consume, obesity occurs gradually. In the past, the health sector attributed obesity to a lack of willpower and self-control that could lead to excessive eating and a lack of physical activity. Today, health professionals are now well aware that obesity is a complex medical problem that is linked to genetic, environmental, behavioural and social factors.

Recent research has also shown that certain genetic factors affect the appetite and metabolism of fats that lead to obesity and increase the risk to a person who is genetically predisposed to weight gain.

While genetic predisposition may contribute to obesity, it is not its main cause. Environmental and behavioural factors exert greater influence, including consumption of excess calories from high-fat foods and little or no daily physical activity. And various psychological factors can also contribute to obesity, such as a sense of worthlessness, guilt, emotional stress, or trauma that can trigger a defensive mechanism such as over-eating.

Some health conditions (binge eating, Cushing’s disease and polycystic ovary syndrome) can also lead to weight gain and obesity.

Risks to your Health

Obesity can lead to significant health risks including respiratory problems (e.g., sleep apnea, asthma), certain cancers (e.g., prostate and colon cancer in men, breast and cervical cancer in women), cardiovascular diseases, reproductive system disruptions, depression, diabetes, gallbladder and liver problems, gastroesophageal reflux disease, hypertension, high cholesterol and musculoskeletal problems.

In addition to physiological complications, obesity is also linked to psychosocial problems such as low self-esteem, discrimination, difficulty finding employment, and reduced quality of life.

Read more: High blood pressure impact on your health

Impacts on Your Sleep

Sleep well

Metabolic Syndrome

Obesity can lead to metabolic abnormalities known as metabolic syndrome. Metabolic syndrome is not a disease, it is a condition that, untreated, can greatly increase your risk of developing several chronic diseases. It is diagnosed when you have three of the following conditions:

  • High blood pressure (≥ 130/85 mm HG, or medication)
  • High blood glucose (≥ 5.6 mmol/L, or medication)
  • High triglycerides (≥ 1.7 mmol/L, or medication)
  • Low HDL cholesterol (< 1.0 mmol/L in men and < 1.3 mmol/L in women)
  • High waist circumference (≥ 102 cm in men, 88 cm in women: may vary depending on ethnicity)

Obstructive sleep apnea is a manifestation of metabolic syndrome. When you do not sleep much or if your sleep is disturbed, you have a tendency to eat more the following day because sleep contributes to regulating hormones such as leptin, which sends out the signal for satiety, and ghrelin, which stimulates the feeling of hunger.

Read more: The impact of sleep deprivation on weight

Find answers with our online screening form.

Healthy tea


Since the risk of obesity in adults depends largely on eating habits adopted during childhood, an effective preventive measure is to instill good behaviour in your children as early as possible. The following tips can help parents:

  • Lead by example.
  • Eat meals together as a family in a pleasant environment without the television.
  • Avoid praising your children when they finish the food on their plate. Eating well is normal behaviour, not a way to please one’s parents.
  • Avoid rewarding or punishing your children using food.
  • Limit your child’s consumption of fruit juices, even natural ones, to one glass per day and give preference to water.


To effectively treat obesity, a change of habits and the adoption of better ones are required over the long term. This is not an easy task. In most cases, mainstream recipes and weight-loss diets do not produce the results expected. Above all, a personalized approach is needed. The best solutions seem to involve a multidisciplinary team consisting of a health care professional for medical and psychological follow-up, a dietician for the preparation of menus, and a kinesiologist or other physical training specialist. Keep in mind that losing 5% to 10% of one’s body weight already leads to measurable health improvements.

If dietary adjustments, physical activity, and the management of stress and psychological issues are not enough, certain medications can be used. In cases of morbid obesity (BMI greater than 40 or BMI greater than 35 with obesity-related disease), bariatric surgery may be the solution.

Why is it so important to eat well for good health? This handy guide clears up some common misconceptions.

Some recommendations from Health Canada

To help you achieve and maintain a healthy weight, Health Canada makes the following recommendations:

  • Reduce the size and frequency of servings by avoiding restaurants that serve large plates or all-you-can-eat meals.
  • Limit the consumption of alcoholic or sweetened beverages, which are high in calories.
  • Set aside time every day to be active: physical activity helps burn a lot of calories!
  • Avoid “miracle” diets that allow you to lose weight quickly and often forbid certain foods. You will quickly regain the weight you lost as soon as you return to a normal diet.

If you are concerned about your weight, consult your health care professional to get a complete assessment and discuss the risks to your health.

For more information on obesity:

World Health Organization

Public Health Agency of Canada

When you need professional support, we're here to help.

We provide services that can help your doctor diagnose sleep disorders and determine the appropriate treatment.

You have question about an equipment? Chat online or get a free teleconsultation with a respiratory therapist.