That's according to an Australian study published in The American Journal of Clinical Nutrition.
Carbs which quickly raise blood sugar (those with a high glycemic index) may hasten sleep, especially when eaten four hours before bedtime, the researchers report.
Such carbs may boost tryptophan and serotonin, two brain chemicals involved in sleep, the study suggests.
The University of Sydney's Chin Moi Chow, PhD, and colleagues studied 12 healthy men who were 18-35 years old.
The men, who had no sleep problems, spent three nights at the researchers' sleep lab. They took one week off between stays at the lab.
Step No. 1: Eat
First, the men fasted for five hours. Afterwards, the researchers served them a meal at the sleep lab.
The basic menu -- rice with steamed vegetables in tomato puree -- was the same each night. But the type of rice and mealtime varied.
One meal included jasmine rice and was served one hour before bedtime.
Another meal featured jasmine rice and was served four hours before bedtime.
The third meal included long-grain rice and was also served four hours before bedtime.
The researchers changed the rice to measure the effects of carbs with high and low glycemic indices. Jasmine rice has a high glycemic index; long-grain rice has a lower glycemic index.
They changed the meal schedule to see whether timing tweaked the carbs' sleep impact.
Step No. 2: Sleep
The men tried all three meals over the course of the study, eating one meal per night. They were free to go to bed whenever they wanted.
The researchers timed how long it took the men to fall asleep once in bed.
The men fell asleep fastest after eating the jasmine rice meal four hours before bedtime. It took them nine minutes, on average, to fall asleep that night.
The men took nearly 15 minutes, on average, to fall asleep after eating the jasmine rice meal one hour before bedtime.
They were slowest to fall asleep after eating the long-grain rice meal four hours before bedtime, taking nearly 18 minutes, on average, to fall asleep.
The meals had no other effect on the men's sleep, the study shows.
Chow's team doesn't know exactly how carbs with a high glycemic index affect sleep.
Although the researchers speculate such carbs raise tryptophan and serotonin levels, making people sleepier, they didn't measure the levels of the brain chemicals in the men.
Adding protein to the meal might change the results, Chow's team notes.
SOURCE: Afaghi, A. The American Journal of Clinical Nutrition, February 2007; vol 85: pp 426-430.
By Miranda Hitti
Reviewed by Louise Chang