Purpose We explored how shift work in UK prison officers and firefighters is associated with body composition, stress, and sleep, and with the quantity, quality, and timing of dietary intake whilst on-shift and off-shift. Methods Secondary analysis of cross-sectional data from an intensive 7 day study on anthropometry, stress, sleeping patterns and dietary intake, obtained in 22 prison officers and 51 firefighters (both male and female), taking part in the neurobiology of food addiction and stress (NeuroFAST) study. Results Mean age was 37.4 ± 7.23 years, while 78% of prison officers and 61% of firefighters were classified as living with either overweight or obesity. Overall, daily energy and total fat intakes were within recommended ranges. However, carbohydrate and dietary fibre intakes were below, while saturated fat and salt intakes exceeded, recommended amounts for health. Prison officers had a significantly lower frequency of breakfast and dinner occasions when on-shift, whereas firefighters had a significantly lower frequency of all eating occasions when on-shift, than when off-shift (all p < 0.001). In prison officers, intake of energy and sugar was significantly higher when off-shift (p = 0.001 and p = 0.002, respectively). Both prison officers and firefighters had higher stress scores during shift days than on non-shift days (p = 0.007 and p < 0.001 respectively). Both groups had longer sleep durations on non-shift days than on shift days (all p < 0.001). Conclusion Prison officers and firefighters had a high prevalence of overweight and obesity and their dietary patterns, and timing of eating occasions, especially when off-shift, may increase risk of metabolic disease