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Ramadan fasting involves marked shifts in sleep–wake cycles, dietary habits, and daily routines, all of which may influence psychological well-being. Although Ramadan represents a naturalistic model of structured, time-restricted fasting, limited research in Saudi Arabia has explored how sociodemographic factors shape mental health, sleep, and eating behaviors during this period. This study examined these outcomes in adults across multiple regions of the country. A descriptive cross-sectional survey was conducted in March 2025 among adults aged 18–60 years residing in Saudi Arabia who observed daytime fasting during Ramadan. A total of 464 participants were recruited through convenience sampling. Data were collected using a validated, culturally adapted questionnaire that assessed psychological well-being, sleep patterns, and eating behaviors. Analyses included descriptive statistics, chi-square tests, and multivariable logistic regression, with p < 0.05 as the significance threshold. Most respondents were female (56.5%) and aged 18–40 years (77.1%). Female sex was significantly associated with depressive feelings and reduced interest (p < 0.05) and independently predicted psychological distress (AOR = 1.35, 95% CI: 1.08–1.72). Adults aged 26–39 and 40–60 years showed higher odds of sleep disturbance and altered eating behaviors (p < 0.05). Participants from the Eastern region demonstrated elevated odds of psychological distress (AOR = 1.80), sleep disturbances (AOR = 2.05), and changes in eating patterns (AOR = 1.50). Employment status was associated with daytime fatigue and non-hunger-driven eating patterns. Ramadan-related lifestyle changes are associated with measurable variations in psychological well-being, sleep quality, and eating behavior. Women, middle-aged adults, and residents of the eastern region appeared to be more vulnerable to these effects. Tailored public health strategies promoting mental health, sleep hygiene, and healthy eating during altered daily routines may help mitigate these impacts.