Circadian rhythms, metabolism and nutrition are closely inter-linked. A great deal of recent research has not only investigated how aspects of metabolic physiology are driven by circadian clocks, but how these circadian clocks are themselves sensitive to metabolic change. At the cellular level, novel feedback loops have been identified that couple circadian ‘clock genes’ and their proteins to expression of nuclear receptors, regulation of redox state and other major pathways. Using targeted disruption of circadian clocks, mouse models are providing novel insight into the role of tissue-specific clocks in glucose homeostasis and body weight regulation. The relationship between circadian rhythms and obesity appears complex, with variable alteration of rhythms in obese individuals. However, it is clear from animal studies that the timing and nutritional composition of meals can regulate circadian rhythms, particularly in peripheral tissues. Translation of these findings to human physiology now represents an important goal. This seminar will highlight protocols for the study of human circadian rhythms and the development serial biopsy analysis. It will then demonstrate how these techniques can be utilised to investigate the interactions between human rhythms, obesity, type 2 diabetes and feeding time.