The volume of food in the gut can impact wakefulness due to sensory fibers in the gut that communicate with neurons in the no-dos ganglia, which then send signals to the brain stem and areas involved in producing neuromodulators.
Sex differences related to karyotype have been found to have a powerful impact on health practices, particularly in response to drugs, different sleep schedules, and overall health practices. Recent studies exploring both sexes have been mandated by institutions such as the National Institutes of Health to explore biases towards only using male subjects.