Introduction: The obesity epidemic is leading to wide-ranging public health problems and potentially reduced life expectancy. This thesis aims to characterise secular trends of anthropometric change among Singaporeans aged 6 to 18 and explore relationships of their latent body mass index (BMI) Z-score growth trajectories during childhood and adolescence on mental health status in later life. It also presents a systematic review of the evidence on the associations of weight change on later life health outcomes. Methods: The uniqueness of this research lies in the development of a new Singapore Longitudinal and Life Course Cohort (SLLCC), an extensive individual-level dataset of repeatedly measured anthropometric data, from about 2.7 million students born between 1973 to 2003, collected through routine annual school-based health screening programmes from 1990 to 2011. Life course growth models were used to model latent developmental trajectories in the SLLCC and age-period-cohort (APC) analyses were conducted to determine secular trends in BMI. Results: Cohorts of people born from 2000 to 2010 had successively higher body weights than cohorts born two decades earlier. These effects were attenuated when cohort influences were removed. Findings from piecewise linear regression and the Zivot-Andrews Unit Root test suggested an upward shift in obesity rates for children aged 6 to 12 years and a levelling off between ages 13 to 18, occurring around the year 2008. In a sub-sample of 519 members of the SLLCC cohort linked with the 2010 National Health Survey, results from latent class growth mixture modelling suggested that individuals who experienced a distinct developmental trajectory of an increasing rate of weight gain from age 10 resulting in obesity at age 16 was associated with a 37% increased risk of later poor mental health well-being, all else held constant. This is the first study to show that cumulative duration of obesity during childhood and adolescence is associated with significant risks of psychological distress later in life. Discussion: The findings from this thesis could lead to new evidence-informed public health imperatives for investments to monitor early childhood growth development so as to mitigate deleterious effects on health, social and economic outcomes in adulthood.