Diagnosis and therapeutic interventions in pathological conditions rely upon clinical monitoring of key metabolites in the serum. Recent studies show that a wide range of metabolic pathways are controlled by circadian rhythms whose oscillation is affected by nutritional challenges, underscoring the importance of assessing a temporal window for clinical testing and thereby questioning the accuracy of the reading of critical pathological markers in circulation. We have been interested in studying the communication between peripheral tissues under metabolic homeostasis perturbation. Here we present a comparative circadian metabolomic analysis on serum and liver in mice under high fat diet. Our data reveal that the nutritional challenge induces a loss of serum metabolite rhythmicity compared with liver, indicating a circadian misalignment between the tissues analyzed. Importantly, our results show that the levels of serum metabolites do not reflect the circadian liver metabolic signature or the effect of nutritional challenge. This notion reveals the possibility that misleading reads of metabolites in circulation may result in misdiagnosis and improper treatments. Our findings also demonstrate a tissue-specific and time-dependent disruption of metabolic homeostasis in response to altered nutrition.Circadian rhythms govern a large variety of behavioral, physiological, and metabolic processes (1-4). Recent advances reveal that a very large fraction of mammalian metabolism undergoes circadian oscillations (5-12). This notion is critical, and it raises awareness of the need for increased attention to the time of monitoring clinically relevant values in patients. Indeed, studies in humans show that levels of key markers oscillate significantly (13-18), possibly leading to false or misleading reads that may result in questionable therapeutic outcomes. Thus, a comprehensive comparative analysis of the circadian metabolome in the serum versus peripheral tissues is critical to decipher the circulating metabolites that constitute a specific signature of a given physiological state.Circadian rhythms are under the control of clocks that ensure cyclic regulation of a large spectrum of cellular and molecular mechanisms. In mammals, the central clock is located in the suprachiasmatic nucleus (SCN) 2 of the anterior hypothalamus. The SCN integrates external daily cues, such as the light-dark cycle, and operates as a synchronizer for a multitude of peripheral clocks located in most tissues (19 -21). Peripheral clocks respond to nutritional cues and can be uncoupled from the SCN by restricted feeding (9,(22)(23)(24). Recent studies have shown that restriction of the time of feeding (9) as well as nutritional challenge by a high fat diet (HFD) (24 -26) result in extensive modifications of liver metabolism. Furthermore, the liver clock displays a highly dynamic homeostasis associated with an elaborate reprogramming of its molecular gears under nutritional challenge (26). Accumulating evidence underscores the intimate interplay between ...