The Facts

Obesity is a leading cause of preventable illness and death in North America. In recent years, the number of overweight people in industrialized countries has increased significantly; so much so that the World Health Organization (WHO) has called obesity an epidemic. In the United States, 69% of the adult population is overweight or obese. In Canada, the self-reported data shows that 40% of men and 27% of women are overweight, and 20% of men and 17% of women are obese.

People who are obese are at a much higher risk for serious medical conditions such as high blood pressure, heart attack, stroke, diabetes, gallbladder disease, and different cancers than people who have a healthy weight.


Obesity occurs when your body consumes more calories than it burns. In the past, many people thought that obesity was simply caused by overeating and under-exercising, resulting from a lack of will power and self-control. Although these are significant contributing factors, doctors recognize that obesity is a complex medical problem that involves genetic, environmental, behavioural, and social factors. All these factors play a role in determining a person's weight.

Recent research shows that in some cases, certain genetic factors may cause the changes in appetite and fat metabolism that lead to obesity. For a person who is genetically prone to weight gain (e.g., has a lower metabolism) and who leads an inactive and unhealthy lifestyle, the risk of becoming obese is high.

Although a person's genetic makeup may contribute to obesity, it's not the primary cause. Environmental and behavioural factors have a greater influence – consuming excess calories from high-fat foods and doing little or no daily physical activity over the long run will lead to weight gain. Psychological factors may also foster obesity. Low self-esteem, guilt, emotional stress, or trauma can lead to overeating as a means to cope with the problem.

Symptoms and Complications

The health risks associated with obesity include:

  • breathing disorders (e.g., sleep apnea, chronic obstructive pulmonary disease)
  • certain types of cancers (e.g., prostate and bowel cancer in men, breast and uterine cancer in women)
  • coronary artery (heart) disease
  • depression
  • diabetes
  • gallbladder or liver disease
  • gastroesophageal reflux disease (GERD)
  • high blood pressure
  • high cholesterol
  • joint disease (e.g., osteoarthritis)
  • stroke

People who are obese may have the symptoms of the medical conditions mentioned above. High blood pressure, high cholesterol levels, breathing problems, and joint pain (in the knees or lower back) are common. The more obese a person is, the more likely they are to have medical problems related to obesity.

Aside from the medical complications, obesity is also linked to psychosocial problems such as low self-esteem, discrimination, difficulty finding employment, and reduced quality of life.

Making the Diagnosis

The diagnosis of obesity is usually based on a physical examination and a patient history (i.e., eating and exercise habits).

A measurement called the body mass index (BMI) does not directly measure body fat, but it is a useful tool to assess the health risk associated with being overweight or obese. A BMI of 18.5 to 24.9 is considered within the healthy range. The BMI is calculated using kilograms (kg) and metres (m) instead of pounds (lb) and inches/feet. Keep in mind that 1 lb equals 0.45 kg and 1 inch equals 0.0254 m.

BMI is calculated as follows:

BMI = body weight (kg) ÷ height² (m)

Example: if you weigh 150 lbs (68 kg) and are 5'8" (1.73 m) tall, divide 68 by (1.73 × 1.73), or 2.99. The result is 22.74, which is right in the middle of the healthy range.

Health Canada classifies BMI according to the associated risk of developing health problems:

BMI value


Health risk

Less than 18.5



18.5 to 24.9

Normal weight


25.0 to 29.9



30.0 to 34.9

Obese class I


35.0 to 39.9

Obese class II

Very high

40 or higher

Obese class III

Extremely high

*The above classification does not apply to people younger than 18 years of age, pregnant women, or breast-feeding women. For people 65 years and older, the "normal" range is higher, beginning slightly above 18.5 and extending into the "overweight" range.

Doctors may also use other measurements, such as waist size, to evaluate health risks associated with excess abdominal fat. When BMI and waist size indicate a high risk for health problems, additional tests may also be performed.

The Canadian Guidelines for Body Weight Classification in Adults are available on the Internet.

Treatment and Prevention

Changing your lifestyle

Obesity is managed and treated to decrease the health risks caused by obesity and to improve quality of life. An appropriate weight management program usually combines physical activity, healthy diet, and change in daily habits. Other programs may also involve psychological counselling and, in some cases, drug therapy. Losing weight and keeping it off is very challenging because lifestyle and behavioural changes are required.

What's important is to eat a healthy, balanced diet. Fad and crash diets don't work and can be dangerous. The body needs a minimum amount of energy from food to function normally. No daily diet with less than 1,000 to 1,200 calories should be used without medical supervision. "Crash diets" are never successful in the long-term because once the diet is stopped, the weight usually comes back. Commercial weight-loss plans and clinics are successful businesses because they have so many return customers.

To lose weight successfully, and to maintain a healthy weight, requires lifelong changes in eating and exercise habits as well as an understanding of emotional factors that lead to overeating. It also involves setting and achieving specific and realistic goals. People who are medically obese should consult a doctor or dietitian for a safe and personalized weight-loss program. Behavioural therapy or modification can also help. Seeing a therapist or counsellor can help you understand the emotional and psychological reasons for overeating and can teach you ways to manage your eating triggers.

Regular physical activity is an important part of weight management. In addition to managing weight, exercise also improves overall health and can help reduce the risk of diseases such as certain cancers, heart disease, and osteoporosis. Regular physical activity doesn't mean you have to join the nearest gym. It can be as simple as climbing the stairs instead of taking the elevator, walking or cycling to work and leaving the car at home (if at all possible), or going for a walk at lunchtime with coworkers. What's important is to add exercise to your daily routine, and to work towards a higher activity level. Choose activities and exercises you enjoy.

Medical intervention

Medications may be part of a weight management program. Medications aren't "magic cures" leading to permanent weight loss. They're generally used in combination with a proper diet and exercise program. They are only for people who are classified as obese (i.e., those with a BMI over 30), or people with a BMI of 27 and extra heart disease risk factors such as high cholesterol or diabetes.

Some medications are approved for short-term use only. One example of a weight-loss medication available in Canada is orlistat*, which blocks the absorption of fat from the bowel. Talk to your doctor about whether medications are an option for you.

Surgery is only considered when other weight management options have not been successful. There are many forms of obesity surgery, but often surgery reduces the size of the stomach so that only a small amount of food can be eaten comfortably. Some of the terms used to describe the surgeries used to treat obesity include:

  • gastric surgery
  • gastric bypass surgery
  • laparoscopic band surgery
  • Roux-en-Y gastric bypass
  • stomach "stapling"

When reviewing suitable management options, it's important to consider the risks and benefits of each option. Your doctor and other health care professionals can provide you with the information you need to make an informed choice about what options are best for you.

*All medications have both common (generic) and brand names. The brand name is what a specific manufacturer calls the product (e.g., Tylenol®). The common name is the medical name for the medication (e.g., acetaminophen). A medication may have many brand names, but only one common name. This article lists medications by their common names. For information on a given medication, check our Drug Information database. For more information on brand names, speak with your doctor or pharmacist.