Familial risk of overweight and obesity in the Canadian population using the WHO/NIH criteria

Objective: To determine the familial risk of overweight and obesity in Canada. Research Methods and Procedures: The sample was comprised of 15,245 participants from 6377 families of the Canada Fitness Survey. The risk of overweight and obesity among spouses and first-degree relatives of individuals classified as underweight, normal weight, pre-obese, or obese (Class I and II) according to the WHO/NIH guidelines for body mass index (BMI) was determined using standardized risk ratios. Results: Spouses and first-degree relatives of underweight individuals have a lower risk of overweight and obesity than the general population. On the other hand, the risk of Class I and Class II obesity (BMI 35 to 39.9 kg/m²) in relatives of Class I obese (BMI 30 to 34.9 kg/m²) individuals was 1.84 (95% CI: 1.27, 2.37) and 1.97 (95% CI: 0.67, 3.25), respectively, in spouses, and 1.44 (95% CI:1.10, 1.78) and 2.05 (95% CI: 1.37, 2.73), respectively in first-degree relatives. Further, the risk of Class II obesity in spouses and first-degree relatives of Class II obese individuals was 2.59 (95% CI: -0.91, 6.09) and 7.07 (95% CI: 1.48, 12.66) times the general population risk, respectively. Discussion: There is significant familial risk of overweight and obesity in the Canadian population using the BMI as an indicator. Comparison of risks among spouses and first-degree relatives suggests that genetic factors may play a role in obesity at more extreme levels (Class II obese) more so than in moderate obesity.