One in three adults in the U.S. and globally suffers from insufficient sleep and/or poor sleep quality, which are associated with poor health outcomes, including all top 10 leading causes of death. Sleep affects health outcomes, in part, by directly and indirectly influencing undesirable dietary behaviors, which, in this work, is defined as frequent consumption of foods that are inconsistent with health. For example, insufficient sleep leads to more frequent consumption of sweets, a direct effect, and stress negatively influences sleep where insufficient and poor-quality sleep can lead to unhealthy dietary behaviors, and indirect effect. Additionally, sleep influences taste measures, such as sweet taste preference; therefore, sleep may also alter dietary intake through changes in taste preference. Singular relationships between sleep, stress, taste measures, and undesirable dietary behaviors and dietary intake have been investigated; however, more complex relationships between these measures have yet to be explored. Therefore, the overall objective of this research was to explore relationships between sleep and undesirable dietary behaviors in a more holistic manner. This was achieved by investigating the role of sleep in the relationship between stress and dietary behavior as well its influence on taste measures and dietary intake relationships.Chapter 2 characterizes and compares health behaviors of higher education students from seven different countries during the COVID-19 pandemic and investigates the effects of changes in sleep duration and quality on dietary risk, alcohol misuse, physical activity, and sitting time. A total of 2,254 students completed the study. Health behaviors were consistent across countries, and students from all countries reported poor sleep quality. Additionally, students who experienced a decline in sleep quality during the COVID-19 pandemic had higher dietary risk scores than students who did not experience a change in sleep quality (p=0.001). Improved sleep quality was associated with less sitting time (p=0.010). The chapter reveals the pressing concern of poor sleep quality that students in higher education were experiencing, and worsened sleep quality was associated with more frequent engagement in unhealthy dietary behaviors. Therefore, addressing poor sleep quality among higher education student is urgent. After investigating how changes in sleep predicted dietary risk, alcohol misuse, physical activity, and sitting time, chapter 3 considers mental health measures and explores more complex relationships between stress, sleep, resilience, undesirable dietary behaviors, and alcohol misuse. This study investigates whether sleep duration and quality mediated and resilience moderated the relationships between stress and undesirable dietary behaviors and the relationship between stress and alcohol misuse. A total of 2,254 students from seven countries completed the study. Results indicated sleep quality, but not sleep duration, mediated the relationship between perceived stress and undesirable dietary behaviors as well as the relationship between perceived stress and alcohol misuse. Further, increased resilience reduced the strength of the relationship between perceived stress and undesirable dietary behaviors but not alcohol misuse. Therefore, chapter 3 demonstrates that students in higher education are likely to benefit from sleep education and resilience trainings, especially during a stressful period. Chapter 4 presents two studies, one methodological and one experimental. The methodological study examined whether a standardized tool used in evaluating sweet taste preference could be used in determining salt taste preference, and the experimental study used the new tool to investigate the effects of sleep curtailment on salt taste measures and explored the relationship between salt taste measures and dietary intake under the habitual and the curtailed sleep conditions. A total of 59 participants completed the study and slept one curtailed night (33% sleep duration reduction) and one habitual night in random order wearing a single-channel electroencephalograph (EEG). Results illustrated the adapted forced-choice paired-comparison tracking test can serve as a valid tool for determining salt taste preference. No changes in salt taste function (slopes of intensity ratings: p=0.844) and hedonic measures (slopes of liking ratings: p=0.074; preferred NaCl concentrations: p=0.092) were observed after a night of curtailed sleep compared to habitual sleep (study 2). However, the slope of liking was associated with energy-corrected Na intake only under the habitual sleep condition (p<0.001). These results suggest that the adapted forced-choice paired-comparison tracking test can be adopted as a tool to assess salt taste preference, and sleep should be accounted for when performing taste studies. In summary, the work presented in this dissertation explores the relationship between sleep and dietary intake in a complex manner. The results reveal 1) poor sleep quality among higher education students is a pressing concern, especially during the COVID-19 pandemic; 2) decline in sleep quality is associated with higher dietary risk, and improvement in sleep quality is associated with less sitting time; 3) sleep quality, but not sleep duration, mediated the relationship between perceived stress and undesirable dietary behaviors and the relationship between perceived stress and alcohol misuse; 4) acute sleep curtailment does not affect salt taste function or hedonic measures; 5) the slope of salt taste liking was associated with energy-corrected Na intake only under the habitual sleep condition. Overall, the work demonstrates the importance of improving sleep, which could reduce dietary risks, alcohol misuse, and sitting time, and the significance of accounting for sleep in taste studies.
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