Youth to adult body mass index trajectories as a predictor of metabolically healthy obesity in adulthood

Background: Adiposity in childhood and adolescence (youth) has been shown to associate with adult metabolic health. What is not known, is whether youth body mass index (BMI) associates with metabolically healthy obesity (MHO) in adulthood, and if so, the age when the BMI to MHO association emerges. This study aimed to determine if BMI trajectories from youth to adulthood differed between adults with MHO and metabolically unhealthy obesity (MUHO).

Methods: The Cardiovascular Risk in Young Finns Study had measured weight and height up to eight times in individuals from youth (3-18 years in 1980) to adulthood (24-49 years). Adult MHO was defined as BMI ≥ 30 kg m^-2, normal fasting glucose (<5.6 mmol l^-1), triglycerides (<1.695 mmol l^-1), high density lipoprotein cholesterol (≥1.295 mmol l^-1 females, ≥1.036 mmol l^-1 males), blood pressure (<130/85 mmHg) and no medications for these conditions. BMI trajectories were compared for adults with MHO and MUHO using multilevel mixed models adjusted for age, sex and follow-up time.

Results: Mean (SD) follow-up time was 29 (3) years. Five hundred and twenty-four participants were obese in adulthood, 66 (12.6%) had MHO. BMI was similar through childhood, adolescence and young adulthood. BMI trajectories diverged at age 33, when individuals with MHO had at least 1.0 kg m^-2 lower BMI than those with MUHO, significantly lower at 36 (-2.1 kg m^-2, P = 0.001) and 42 years (-1.7 kg m^-2; P = 0.005).

Conclusion: Adult MHO was characterized by lower adult BMI, not youth BMI. Preventing additional weight gain among adults who are obese may be beneficial for metabolic health.