High-GI foods aid sleep? Dream on!

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Insomnia can be a debilitating problem. Not only can it leave people feelings seriously low on physical and mental energy, but shortened sleep has also been linked with a range of long-term health issues including heart disease, diabetes and weight gain. For a variety of reasons, what we eat and drink may affect sleep, and this was the subject of a study just published in the American Journal of Clinical Nutrition [1].

In this research, individuals were fed one of two different suppers to see what effect this had on the amount of time individuals required to get off to sleep four hours later. Both these evening meals contained the same amount of calories. The main difference between them was their glycaemic index ” a measure of the extent to which they release sugar into the bloodstream. While one meal had a moderate GI of 50, the other has a whopping GI of 109. The researchers in Australia who conducted this study found that compared to the low-GI meal, the high-GI one halved the time to sleep onset (an average of 9 minutes compared to 17.5 minutes).

The overriding message from this study appears to be that eating a high GI supper can help reduce a tendency to insomnia. I am not surprised by this because eating high GI foods are likely to cause the body to secrete copious quantities of the hormone insulin, which can drive blood sugar levels to subnormal levels some time (typically 2-4 hours) later. Low blood sugar can sure induce some sleepiness, so no wonder then that individuals find eating high-GI foods for supper help them get to sleep.

But this phenomenon only tells a part of the story. In the long term, gluts of insulin can induce a range of ills including Type 2 diabetes, heart disease and weight gain. Let’s be clear: Even if high-GI foods help individuals get to sleep, they are still a major hazard to health.

Also, while high-GI foods may possibly help people get to sleep, they will almost certainly do nothing to help people stay asleep.

When blood sugar levels drop in the night, one method the body has to correct this is to liberate sugar from fuel stores such as glycogen in the liver. Problem is, to effect this change, the body secretes ‘stress’ hormones such as adrenaline (epinephrine) and cortisol. Trust me when I tell you is the last thing you need in the middle of the night when you’re aim is deep, restful sleep is to have stress hormones whooshing around your system. This can manifest as waking in the night, often at some time between 3.00-4.00 am. The stress hormone surge caused by low blood sugar can cause individuals to be very awake and alert at this time, and they also may have considerable difficulty getting off back to sleep again until, quite often, about half an hour before the alarm goes off.

It is this phenomenon which helps to explain why it is that individuals who wake in the night often work out for themselves that eating something often helps to get them back to sleep.

Those wishing to avoid the need to go ferreting for food in the kitchen in the middle of the night will almost always benefit from taking steps to stabilise blood sugar levels. A low-GI supper (e.g. meat, fish, pulses, vegetables) is the way to go here, perhaps with a little snack of, say, some fruit and nuts, before bedtime. Getting blood sugar levels nice and stable really does help to keep us asleep at night. It also helps to keep us awake during the day too.


1. Afaghi A, et al. High-glycemic-index carbohydrate meals shorten sleep onset. Am J Clin Nutr 2007 85: 426-430

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