Final answer:
L-tryptophan affects sleep by playing a role in the synthesis of serotonin and melatonin, neurotransmitters that regulate sleep-wake cycles.
Step-by-step explanation:
L-tryptophan affects sleep by playing a role in the synthesis of the neurotransmitter serotonin, which is involved in regulating sleep-wake cycles. Tryptophan is converted into serotonin, which can then be further converted into melatonin, a hormone that helps regulate sleep. Serotonin levels are generally higher during daylight hours and decrease at night, while melatonin levels increase in the evening and peak during the night, promoting sleep. Therefore, consuming foods rich in tryptophan, such as turkey, milk, and nuts, may indirectly promote better sleep.