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There is evidence which suggests that sleep behavior and dietary intake are interlinked. Thus, we investigated whether a seasonal rhythm in food-energy density exists, and how this relates to quality of sleep.Two hundred and thirty adult volunteers were investigated across the four seasons. Anthropometrical measurements were obtained and The Pittsburgh Sleep Quality Index was used for an assessment of sleep quality and disturbances. The dietary intake was evaluated using a 24 h dietary recall. Generalized estimating equations were used to estimate seasonal changes in energy density and sleep quality, as well as the association of energy density with sleep quality. All analyses were adjusted for age, sex, education, occupation and shift-work.Mean food energy density was significantly higher in winter as compared with other seasons (P < 0.05), although no seasonal variations were observed in macronutrient intake (fat and protein). Overall, the sleep quality was low (score value > 5) in all seasons, with the lowest quality occurring in winter and the highest in spring (P < 0.05). The components of sleep quality score showed that winter had statistically (P < 0.05) poorer subjective sleep quality, sleep latency and sleep disturbances, but lower daytime dysfunction compared with spring and summer. After adjusting for seasonal effects (correlated outcome data) and shiftwork, energy density was found to be inversely associated (P < 0.0001) with sleep quality.An inverse association between seasonal fluctuation of food energy density and sleep quality was found with winter time, associated with the intake of higher energy dense food products and the lowest sleep quality.