In conclusion, the results of the present study demonstrate that rats fed a powdered diet exhibited less NREMS during the early dark, active/feeding phase compared with rats fed a pelleted diet. This may be due to the reduced mastication required to consume a powdered diet. Further studies are needed to examine the physiological mechanisms responsible for this effect, particularly the involvement of orexin and histaminergic pathways in the central nervous system, and the potential role of the post-prandial glycemic response.