Many people experience difficulty in getting off to sleep. Scientists have shown that carbohydrate foods with a high Glycaemic Index (GI) may induce a quicker sleep onset.

GI  tells us how quickly a carbohydrate food is absorbed by the body. High GI foods include rice, potatoes, white bread and soft drinks. In contrast, low GI foods include pasta, beans, fruit and vegetables.

In a study looking at sleep onset and quality, 12 healthy men were asked to consume different test meals either 1 hour or 4 hours before going to bed. The rice-based meals varied in GI, but calorie (energy), fat and protein levels were similar. The results showed that subjects fell asleep within 9 minutes when they ate a high GI meal. Sleep onset increased to 17 ½ minutes when subjects ate a low GI meal. These effects were apparent when the meal was eaten 4 hours before bed-time. Eating the meal 1 hour before bedtime had a minimal impact on sleep onset. No changes in sleep quality were seen with either of the meals.

Dietary carbohydrate is likely to have an effect on sleep because it increases blood levels of a protein component called tryptophan. Tryptophan is used by the body to make serotonin, which is a well-known sleep-inducing agent. The high GI meals taken 4 hours before bed probably maximise serotonin levels, helping sleep to occur more quickly.

For more information see Afaghi A et al (2007). High-glycemic-index carbohydrate meals shorten sleep onset. American Journal of Clinical Nutrition, vol 85: pp 426-30.

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Nutrition - Carbohydrates