Day Versus Night: Within-Person Associations in Diet Quality Among Shift Workers in Urban Thailand

Background: As the 24-h economy expands, an increasing share of the global workforce engages in nighttime work. Most previous studies have documented adverse effects among healthcare workers and in high-income countries. Evidence in low-income earners in low- and middle-income countries is limited. This study analyzed the association between night shift work and the diets of convenience store workers in Bangkok, Thailand, focusing on fruit and vegetable intake. Methods: The study used a within-person repeated-measures design with questionnaires administered to 100 convenience store workers in Bangkok during their regular daytime and nighttime shifts. The Diet Quality Questionnaire (DQQ) was used and relied on self-reported food intake over the past 24 h. Data were analyzed using a paired t-test and panel regression. Predictors included food sources and personal domains of the food environment. Results: Mean fruit and vegetable intake was 198 g per day, half the amount recommended by the World Health Organization. There was no statistically significant difference in combined fruit and vegetable intake between days with a day shift and days with a night shift for both the panel logistic regression (p = 0.184) and the paired t-test analysis (p = 0.156). However, diet diversity (MD = 0.40, SEMD = 0.16, p < 0.05) and the non-communicable disease (NCD)-Protect score (MD = 0.61, SEMD = 0.17, p < 0.01) statistically differed across shifts. Night shifts were associated with lower diet diversity (B = −0.41, p < 0.01) and reduced NCD-Protect (B = −0.63, p < 0.001). The number of convenience store visits was significantly associated with NCD-Protect (B = −0.45, p < 0.01). Conclusions: Night shift workers generally have low fruit and vegetable intake. Night shift work is negatively associated with dietary diversity and intake of protective foods. There is a need for employer and policy measures to protect shift workers’ health regardless of work hours.