Young adults gain more weight annually than other adult age group. Foods prepared outside home such as fast food have been implicated in increased energy consumption and obesity. The current study explores the associations of body mass index (BMI) and energy consumed from fast foods among young adults in Australia.


A cross-sectional study was conducted among 1001 diverse participants aged 18 to 30 years. Each participant recorded all food and beverages consumed over three days using a purpose-designed smartphone app. Data on weight, height and other sociodemographic variables were collected. The proportion of total energy consumed from food prepared at fast food outlets was calculated. The relationship between BMI and proportion of fast food energy was examined using multivariate linear regression with adjustment for gender, socioeconomic status (SES) and geographic location (metropolitan, regional and rural). SPSS was used for all analyses.


The mean proportion of energy from fast food was 14.7 (SE 0.8) % for males and 9.8 (SE 0.5) % for females. BMI showed a positive association with proportion of energy intake from fast food chains (β= 0.3, SE 0.1 % kJ with each unit increase in BMI; p<0.003). Percentage energy from fast food was also positively associated with being male (β= 4.9, SE 0.1, p<0.001) and of lower SES (β= 3.5, SE 1.0, P<0.001).


BMI is positively associated with fast food consumption in young adults. However, the observed relationship cannot be considered causal and it may be that those with higher BMI favor fast food.