Background Worldwide consumption of ultra-processed foods is continued to rise. Growing evidence has linked ultra-processed food consumption with elevated risks of obesity, non-communicable diseases, and mortality in adults. Associations between ultra-processed food consumption and long-term adiposity trajectories have never been investigated in children.

Methods Data were obtained from the Avon Longitudinal Study of Parents and Children (ALSPAC), a prospective birth cohort study conducted in Avon County, south-west England. Participating children with baseline dietary intakes collected using 3-day food diaries and repeated measures of adiposity outcome were included and followed up from ages 7 to 24 years (1998–2017). Adiposity outcomes included objectively assessed anthropometrics (body mass index, weight, waist circumference) and dual-energy X-ray absorptiometry measurements (fat and lean mass index, body fat percentage). All foods and drinks consumed were categorised according to the degree of processing applying the NOVA food classification system. Individual’s consumption of ultra-processed foods was derived as a percentage of its weight contribution (gram per day) in the total diet and categorised into quintiles. Associations between quintiles of ultra-processed food consumption and trajectories of adiposity outcomes were evaluated using linear growth curve models and adjusted for study covariates.

Results A total of 9025 children (49.6% female) were followed up over a median (IQR) of 10.2 (5.2–16.4) years. Mean (SD) ultra-processed food consumption at baseline from the lowest to highest consumption quintiles was 23.2% (5.0%), 34.7% (2.5%), 43.4% (2.5%), 52.7% (2.8%) and 67.8% (8.1%). Trajectories of body mass index, fat mass index, weight and waist circumference increased significantly by an additional 0.06 (95% CI, 0.04 to 0.08) kg/m², 0.03 (95% CI, 0.01 to 0.05) kg/m², 0.20 (95% CI, 0.11 to 0.28) kg and 0.17 (95% CI, 0.11 to 0.22) cm per year among those in the highest quintile of ultra-processed food consumption compared with their lowest quintile counterpart. Evidence of dose-response relationships were consistently observed with those in the two highest quintiles of ultra-processed food consumption showing significantly more rapid progression of body mass index, weight, and waist circumference.

Conclusion These findings provide important and novel evidence that higher consumption of ultra-processed foods is associated with more rapid progression of adiposity from childhood to early adulthood. Radical and effective public health actions that reduce children’s exposure and consumption of ultra-processed foods and encourage greater consumption of minimally processed foods are urgently needed to counteract the growing burden of obesity in England and globally.