Changes in body mass index in Canadians over a five-year period: Results of a prospective, population-based study

Height and weight were measured at baseline and 5 years and used to calculate BMI and assign one of six weight categories. Multiple imputation was used to adjust for missing weight at year 5. Data were stratified by age and gender. The proportion of participants moving between categories was generated, and multivariable linear regression was used to identify factors associated with weight change.Baseline data were available for 8548 participants, year 5 data for 6721, and year 5 weight was imputed for 1827 (17.6%). Mean BMI for every age and gender group exceeded healthy weight guidelines. Most remained within their BMI classification over 5 years, but when change occurred, BMI category was more likely to increase than decrease. Several sociodemographic, lifestyle and clinical characteristics were associated with change.Mean baseline BMI tended to be higher than recommended. Moreover, on average, men under age 45 and women under age 55 were gaining approximately 0.45 kilograms (one pound) per year, which leveled off with increased age and reversed in the oldest age groups. These findings underscore the need for public health efforts aimed at combating obesity.The World Health Organization has recommended an updated classification system for the assessment of body mass index (BMI, defined as weight in kilograms divided by height in meters squared) in adults [1]. This system defines underweight as a BMI of < 18.5, normal as 18.5–24.99, overweight as 25.0–29.99, and includes three classes of obesity for those with a BMI of 30.0–34.99, 35.0–39.99, and ≥ 40.0 [1,2]. Given this new classification, it is helpful to understand changes in BMI over time in the general population.It is widely accepted that given a certain height, there is a range of weight that is associated with good general health [2,3]. Despite this knowledge, there is evidence that the prevalence of being overweight or obese is reaching epidemic proportions across all age groups, both in developed and deve