Scientists have discovered that eating lots of rice can trigger a deep slumber, while pasta and noodles can actually hinder sleep.
The Japanese researchers also found eating bread products – including white bread, pancakes and pizza – had no effect on the quality of sleep.
They say eating food high on the glycaemic index (GI) – such as rice – was found to be associated with good quality sleep.
Foods with a high GI release sugar in the blood more quickly, leading to spikes in blood sugar levels that can last for a longer time.
Low GI foods, on the other hand, tend to cause small blood sugar rises that don’t last as long.
A high GI diet may affect sleep quality because of the effects of tryptophan, an amino acid known for its tranquilising effects and link to the sleep-inducing hormone melatonin.
This backs up previous research which found eating a meal high in carbohydrate – with a high GI – increased the amount of tryptophan being transported into the brain compared with other amino acids.
In the brain, tryptophan is converted into serotonin and then to melatonin, which induces sleep.
According to the study, people in Japan consume up to ten times more rice than those in Europe and North America.
Rice accounts for approximately 28 per cent of the Japanese people’s daily energy intake.
The study analysed data from the annual health examinations of 1,848 factory workers (1,164 men and 684 women).
The Industrial Health and Safety Law in Japan requires that employers offer annual health examinations to all of their employees, so this data could be used by researchers.
The participants also answered a questionnaire in 2003 and a year later in 2004 on health-related behaviours such as their diet, whether they smoked and how much exercise they took.
To assess the participants’ sleep quality, researchers used the Japanese version of the Pittsburgh Sleep Quality Index, which assesses a person’s quality of sleep.
This looked at sleep quality; the amount of time it took to fall asleep after the lights were turned off, duration, efficiency, disturbances, use of medication and how the workers felt and performed during the day.
Those with a higher rice intake and higher GI intake scored much better on the sleep scale – i.e. they slept well.
The researchers also found a higher rice and GI intake were linked with better sleep duration.
Higher noodle intake, however, was associated with a more frequent sleep disturbance, higher levels of daytime dysfunction, increased use of sleep medication, poorer subjective sleep quality, and taking longer to get to sleep, they found.
Bread consumption was not found to be linked to sleep quality.
Writing in the study, the researchers said: ‘The present study indicates that high consumption of rice and a high dietary GI are associated with good sleep, especially good sleep duration.
‘Meanwhile, higher noodle consumption is associated with poor sleep quality. The effects of starchy foods on sleep may differ according to their GI values.
‘Diets with a high-GI, especially those with high rice intake, may contribute to good sleep.’