There has been some evidence that carbohydrates improve sleep in children. This data led to a recent study in PLoS ONE, which examined this phenomenon in adults. Specifically, the study asked how a carb source’s glycemic index (GI) can influence sleep quality.
Study Design
This study investigated how three specific carb sources – rice, pasta, and bread – affect sleep quality. The idea was pretty simple: the researchers compared the amount a person consumed of each of these three foods to how well they slept. Each carb source was broken down into more specific types of rice, pasta, and bread (for example, white bread versus whole wheat) to get a better idea of the GI of each.
Participants all worked at the same factory in Japan and represented a large swath of the population, including men and women from twenty to sixty years of age. This reduced the influence of standard age differences found in sleeping, which was also factored out in all of the equations. The subjects were all considered white collar workers. This was because many of the blue collar employees worked nights, which could have confused the results.
Results
The carb sources did indeed influence sleep. Specifically, rice improved sleep quality and pasta reduced sleep quality. Bread showed a pretty weak trend toward worse sleep quality, but as it was the least consumed of the three sources, perhaps there was not enough information to be certain.
In addition to the carb sources themselves, the GI of the carb source correlated with sleep quality, with higher values meaning better sleep. Glycemic load (which also accounts for the total amount of carbohydrate) also trended toward better sleep, but this correlation was not quite strong enough for statistical significance.
The major reason for improved sleep was increased average length of hours slept. A higher glycemic load also correlated with decreased need for sleeping medications.
We typically consider higher glycemic carb sources to be lower quality and less healthy than lower glycemic carbs. Carbs with a higher glycemic index absorb into the bloodstream much more quickly. Apparently the higher absorption rate improves sleep quality, either by making you sleepier or helping control your sleep-wake cycles.
It looks like an average dietary GI in the upper sixties is where the changeover occurs quite rapidly from a negative to a positive effect on sleep. In other words, if your average carb source absorbs into your blood stream faster than a banana, which has a GI in the low sixties, your sleep quality might improve. Pasta tends to have a low GI – in the forties when cooked right – whereas white rice is in the upper eighties.
Conclusions
These results help explain the sleep disturbances experienced by many paleo dieters and other low-carb eaters. Many of the carbohydrate sources consumed in low-carb diets have a low GI as well. The GI of a carrot, for example, is in the mid thirties. Few undried fruits surpass bananas, with a notable exception being watermelon. If you are on a low-carb and low glycemic-diet, your sleep quality may take a hit.
Happily, exercise has a similar effect to carbohydrates on sleep, especially in conjunction with carbohydrate intake. If you find you are struggling with your own sleep quality, especially if you wish to continue eating healthy carb sources with a low glycemic value, make sure to focus on eating carb sources with your protein sources post-workout. Try to also get some fruit close to bedtime.
References:
1. Satoko Yoneyama, et. al., “Associations between Rice, Noodle, and Bread Intake and Sleep Quality in Japanese Men and Women,” PLoS ONE 9(8), 2014
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