Circadian lipid and hepatic protein rhythms shift with a phase response curve different than melatonin

While studies suggest that light and feeding patterns can reset circadian rhythms in various metabolites, whether these shifts follow a predictable pattern is unknown. We describe the first phase response curves (PRC) for lipids and hepatic proteins in response to combined light and food stimuli. The timing of plasma rhythms was assessed by constant routine before and after exposure to a combined 6.5-hour blue light exposure and standard meal schedule, which was systematically varied by ~20° between individuals. We find that the rhythms shift according to a PRC, with generally greater shifts for lipids and liver proteins than for melatonin. PRC timing varies relative to the stimulus, with albumin and triglyceride PRCs peaking at a time similar to melatonin whereas the cholesterol and high-density lipoprotein PRCs are offset by ~12 h. These data have important implications for treating circadian misalignment in shiftworkers who consume meals and are exposed to light around the clock. A key property of circadian rhythms is that they can be reset in response to environmental time cues; this response is described by a Phase Response Curve (PRC). Here the authors describe PRCs for resetting circadian rhythms in lipids and hepatic proteins in response to combined light and food exposure.