CMET he prevalence of obesity in adults has increased worldwide and has almost doubled in Canada, from 14% in 1978/79 1 to 26% in [2009][2010][2011]2 with 2% of men and 5% of women having a body mass index (BMI) score greater than 40 (Appendix 1, available at www .cmaj.ca/lookup/suppl/doi :10.1503/cmaj .140887 /-/DC1).3 Over two-thirds of Canadian men (67%) and more than half of Canadian women (54%) are overweight or obese, based on measured weight.2-4 Excess weight is a well-recognized risk factor for several common chronic conditions, such as cardiovascular disease, cancer, type 2 diabetes, osteoarthritis and back pain.
5About two-thirds of adults who are overweight or obese were in the healthy weight range as adolescents, but gained weight in adulthood (about 0.5-1.0 kg every two years on average). 6,7 Slow weight gain may go unnoticed until health problems develop in middle age. However, this overall mean increase masks substantial variation in the population, and some people remain weight stable over long periods, whereas others experience substantial gains and losses. Currently, we cannot predict future health effects of weight gain over the life course.The causes of obesity are complex. Although excess adiposity is ultimately the result of an imbalance in the amount of energy consumed and the amount of energy expended by an individual, there are many biological, behavioural, social and environmental factors that interact to affect this balance. The dramatic increase in obesity since the 1970s, however, suggests environmental causes are prominent and potentially amenable to interventions and prevention. 8,9 Possible approaches include a wide range of legislative and policy options, in addition to health-promotion advice to maintain a healthy weight, increase physical activity and eat a healthy diet.10 Primary care providers have an important role in preventing and managing obesity through services offered to patients.Overweight or obese status is commonly assessed using the BMI. The internationally recognized cut-off BMI values for adults are as follows: underweight (< 18.5), normal weight (18.5-24.9), overweight (25-29.9) and obese (≥ 30). The obese category is further broken down by BMI into class I (30.0-34.9), class II (35.0-39.9) and class III (≥ 40).11 Distribution of body fat is also an independent indicator of health risk, and high waist circumference is associated with an increased risk for cardiovascular disease and type 2 diabetes.
12Lifestyle interventions (e.g., behavioural therapies, and dietary and physical activity programming and support) are the first line of treatment for most patients with overweight or obesity. Pharmacotherapy and surgery are options for more severe cases of obesity. A weight loss of 5% is considered clinically important, 13 as many cardiovascular risk factors (e.g., elevated blood pres-
