Falling Asleep and Food

Summarized by Robert W. Griffith, MD
March 22, 2007

Summary

In healthy young volunteers, a high-glycemic-index meal taken 4 hours before bedtime had the effect of almost halving the time taken to fall asleep, from an average of 17½ minutes to 9 minutes.

Introduction

Many people complain about difficulty in falling asleep. (Of course, they complain about staying asleep and waking too soon, but those are different problems.) The falling-asleep time is known technically as 'sleep onset latency' (SOL), and it can be improved, or shortened, like the other sleep problems, using cognitive behavioral therapy.¹ But Australian researches wondered if there could be another approach - changing the content of the evening meal. Dietary carbohydrate has been shown to increase the plasma concentration of tryptophan, which is used to synthesize serotonin, a sleep-inducing agent that acts by increasing melatonin at the appropriate time of day.

High-glycemic-index (GI) carbohydrates² increase the amount tryptophan in the blood by releasing insulin, while a high protein meal contributes less tryptophan. The researchers investigated the effect of a high-GI meal 4 hours before bedtime on sleep onset latency, comparing it with a low-GI meal. This is a summary of their publication in the American Journal of Clinical Nutrition.

What was done

The study employed 12 healthy male volunteers aged 18 to 35; they had to have a normal body mass index (BMI), i.e. between 18.5 and 25. They completed a 2-week sleep diary before having a familiarization night in the sleep lab. Then, one week apart and in randomized order, they were given one of the following evening meals: a high-GI meal 4 hours before bedtime; a high-GI meal 1 hour before bedtime; and a low-GI meal 4 hours before bedtime. On these evenings they slept in the sleep lab.

The meals all had the same total calories and included 600 g of steamed rice; the rice was either low- or high-GI (values of 50 and 109, respectively). On test days, the subjects fasted for 5 hours before their evening meal. Blood glucose levels were measured at intervals after the test meals. Urine was collected for measuring a melatonin derivative, after the meal and an overnight sample.

A sleep electroencephalogram (sleep EEG) on the test nights allowed the total sleep time and SOL to be recorded.

What was found

The average SOL 4 hours after the low-GI meal was 17.5 minutes; 4 hours after the high-GI meal it was almost halved - 9.0 minutes. This difference was statistically significant. All the 12 subjects showed a reduction in SOL except one, who showed an increase. Blood glucose levels showed, as expected, a significantly greater response to the high- than the low-GI meal, although by 2 hours after the meals average values were similar for the two groups. There were no significant differences in the melatonin output between the two 4-hour groups.

The SOL one hour after the high-GI meal was 14.6 minutes, significantly different from that of the 4-hour high-GI meal. There were no other effects on sleep patterns.

What these findings mean

A high-glycemic-index meal taken 4 hours before bedtime had the effect of almost halving the time taken to fall asleep, from an average of 17½ minutes to 9 minutes. Before we attach too much importance to this, however, we should remember that the subjects were normal young men without reported sleep problems. If this approach is to be of practical use, the results should be confirmed in patients with sleep disturbances. And if the findings should be reproducible in such patients, they may lead the way to a better therapeutic alternative than medications that are often associated with a number of side effects.

Possible benefits of a high-GI evening meal on sleep patterns will have to be set against disadvantages of such a meal in diabetics. Improved sleep - or at least longer sleep - has been reported to assist with weight control or even weight loss, a desirable feature for many diabetics. However, a high-GI meal, with its increased glucose and, by imputation, insulin release, may not be metabolically desirable. It's become well-accepted that low-GI meals usually keep one satisfied for longer. "They help you burn more of your body fat and less of your body muscle" according to one expert. Something to think about, while you're waiting to fall asleep...

Source

• High-glycemic-index carbohydrate meals shorten sleep onset. A. Afaghi, H. O'Connor, CM. Chow, Am J Clin Nutr , 2007, vol. 85, pp. 426--430

Footnotes
1. Cognitive behavior therapy (CBT) combines two very effective kinds of psychotherapy - cognitive therapy and behavior therapy. Cognitive therapy shows you how certain thinking patterns are causing your symptoms by giving you a distorted picture of what's going on. Behavior therapy helps you weaken the connections between troublesome situations and your habitual reactions to them. It teaches you how to calm your mind and body, so you can feel better, think more clearly, and make better decisions. When combined into CBT, cognitive therapy and behavior therapy provide powerful tools for stopping your symptoms and getting your life on a more satisfying track.
2. The glycemic index (GI) is a ranking of carbohydrates on a scale according to the extent to which they raise blood sugar levels after eating. Sugar and white bread have a score of 100. Foods with a high GI are those which are rapidly digested and absorbed and result in marked fluctuations in blood sugar levels. Low-GI foods, by virtue of their slow digestion and absorption, produce gradual rises in blood sugar and insulin levels, and have proven benefits for health.

Related Links
Sleep Disorders
The Glycemic Index
Search the Glycemic Index Tool

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