METABOLIC FACTORS. “Also, metabolomics analyses in human serum, plasma, and skeletal muscle have identified major populations of rhythmic metabolites over the circadian cycle.”
https://www.nature.com/articles/s41591-018-0271-8?fbclid=IwAR01C2Z4J5lxVYDLhxIb9dPb3fhNSZSxwimZvhHaJ4n3-nVPpkt2PNqoukk