Background Early adulthood is typically a period of poor diet and rapid weight gain. It is also an age of transition, including changes in social and physical environments which may be associated with changes in health-related behaviours. We examine the association of five life transitions (leaving the family home, leaving full-time education, beginning full-time employment, beginning cohabitation, and becoming a parent) with change in fast food intake.

Methods We used four waves of data from adolescence (mean age 15) through early adulthood (to mean age 31) from the longitudinal, population-based Project EAT study (Minnesota, US). The underlying trajectory of fast food intake was modelled as a latent growth curve. Additional latent intercepts at waves 2, 3 and 4 were included, regressed on the 5 life transitions, to allow for additional effects of experiencing life transitions between waves. All life transitions were included in a single model allowing adjustment for other transitions and the underlying growth curve.

Results Fast food was consumed 1.69 times/week (SE 0.03) at age 15, and followed a negative quadratic trajectory through early adulthood. Beginning full-time employment and becoming a parent were associated with increases in fast food intake of 0.16 times/week (SE 0.007) and 0.16 times/week (SE 0.004) respectively. Leaving the family home and beginning cohabitation were associated with decreases in fast food intake of -0.18 times/week (SE 0.003) and -0.16 times/week (SE 0.008) respectively. Leaving full-time education was not associated with any change in fast food intake (-0.01 times/week (SE 0.89)).

Conclusion Social transitions in early adulthood contribute to changes in fast food consumption, which may affect dietary intake and long-term health. These findings suggest a further focus on the life transitions of beginning employment and becoming a parent for public health policies and intervention.