We tested a battery of potential mechanisms involved in the effect of feeding on the ChP clock, such as changes in glucose, temperature, selected feeding-related hormones, and osmolarity, of which we identified changes in glucose levels in the CFS as the most potent mediator that may affect the ChP clock via O-GlcNAcylation. The gene discussed is CLOCK; the disease is myalgic encephalomeyelitis/chronic fatigue syndrome.