Certain food constituents seem to have effects on rhythm adjustment. A high carbohydrate low protein meal, facilitating brain uptake of tryptophan and its conversion to serotonin, may induce drowsiness and sleep. On the other hand, a high protein low carbohydrate meal, which enhances tyrosine uptake and convertsion to noradrenaline, increases levels of arousal. Moreover, programmed use of theophylline and caffeine can speed rhythm readaptation and help to raise arousal levels in the morning. However, although studies on military personnel consuming such diets reported reduced sleep disturbance and less subjective feelings of fatigue in the days immediately after a transmeridian flight compared with controls, a clear link between diet and jet lag has not been formally established. Two studies have investigated the effects of light treatment on sleep patterns after flights. In the former, 19 subjects returning to the United States from Oriental or South Pacific localities (advance shifts of 6.5 to 10 hours) were instructed to expose themselves to either bright white light (2000 lux) or dim red light (<100 lux) for 2 or 3 hours on awakening in the morning for 3 days.” No differences were found between the group means for any sleep measure, but exposure to bright light early in the morning appeared to facilitate the consolidation of sleep into a single night-time episode.In the latter, four subjects were polysomnographically recorded before and after a flight from Tokyo to San Francisco (8 hour advance).” In San Francisco, the subjects were requested to go bed at 2300 hours and wake up by 1000 hours and were exposed for 3 consecutive days to either bright ( > 3000 lux) or dim ( <500 lux) light for 3 hours starting at 1100 hours (0300 hours Tokyo time). The bright light treatment seemed to be effective in accelerating circadian re-entrainment.However, the sparse number of field studies and the small sample population considered do not yet allow a clear judgment on the beneficial effect of bright light treatment for jet lag.61 In fact, the Consensus Report for Light Treatment for Sleep Disorders concluded that “much remains to be learned before procedures can be developed that are at once effective, reliable, and practical. For this to happen, optimal combinations of several light exposure parameters must be first defined and tailored to specific flight situations”.