Problems with sleep and eating are common among patients with a bipolar disorder (BD). While learning to control rhythms is a common and evidence based aim of psychotherapy, no naturalistic study has explored correlations between sleep and eating rhythms. Consenting BD patients (n=75) completed hourly charts of mood and eating occasions for two weeks. Sleep was calculated based on periods of inactivity derived from actigraphy recordings (≥10 days). In addition to conventional sleep onset/offset, we calculated center of daily inactivity [CenDI] as a measure of sleep phasing, and consolidation of inactivity [ConDI] as a measure of sleep fragmentation. The regularity of eating patterns was assessed by quantifying the stability of eating events with regard to timing [I^TIM] and intervals [I^INT]. Sleep timing variability and fragmentation was robustly associated with eating irregularity, despite several other factors thought to mask this chronobiological association in humans with a psychiatric illness. Future work should confirm whether this relationship is causal, bidirectional and/or consequence of a shared dysregulation. The finding provides a theoretical framework for therapeutic interventions in improving outcome in BD. Our novel dimensional measures for sleep and eating patterns could serve as helpful tools for biofeedback and diagnostic and intervention assessment.