Objective

Smartphone use, psychological stress, and sleep quality are increasingly recognized as lifestyle factors that may influence dietary behaviors in young adults; however, their associations with overall diet quality remain unclear.
Methods
This cross-sectional study investigated the associations of daily smartphone use, perceived stress, and perceived sleep quality with diet quality and macronutrient intake among 497 Korean adults aged 20–39 years. Diet quality was assessed using the Nutrition Quotient for Korean Adults 2021 (NQ-2021), and dietary intake was evaluated using a 24-hour dietary recall.
Results
Longer smartphone use was inversely associated with total NQ and practice scores after adjustment for potential confounders. Participants with higher perceived stress consumed a greater amount of carbohydrates and a lower amount of fat per 1,000 kcal, whereas total NQ scores did not differ according to perceived stress level. Participants reporting poorer sleep quality had significantly lower total NQ, balance, and moderation scores and lower protein intake than those with better sleep quality.
Conclusion
These findings suggest that self-reported smartphone use, perceived stress, and perceived sleep quality are associated with different aspects of diet quality and macronutrient intake among Korean young adults. Prospective studies using validated or
objective
measures are warranted to clarify the temporal relationships between these lifestyle-related factors and dietary behaviors.