High-Carbohydrate Diet And Sleep

Last updated: July 1, 2019

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Do you get sleepy after eating a lot of carbohydrates? Does that mean carbs are good for your sleep quality? There are many questions about the connection between carbs and sleep and not so many clear answers.

So far the research suggests that a meal rich in carbohydrates makes us fall asleep faster. However, some studies have shown a decrease in slow-wave sleep (deep, restorative sleep). This change may only happen in the first sleep cycle, although some research shows that carbs from sugar disrupt sleep efficiency (cause wakings) so then we could say that entire sleep quality depends on what we eat.

Deep sleep and REM sleep are important for numerous reasons – our overall health, mood, cognitive functions, and the feeling of restfulness depend on them. Having less deep and REM sleep can result in non-restorative sleep which leaves us groggy and tired the next day.

Eating carbs before sleep

Carbohydrates do make us sleepier. If you have a high-carb meal an hour before bed, you likely won’t see the benefits but you will have a significantly shorter sleep onset time if you have the same kind of meal four hours prior to your bedtime.

A study was conducted on twelve young healthy men who were given meals four hours before their typical bedtime consisting mainly of rice (either of low- or high-glycemic index). They also had high-glycemic index rice one hour before sleep time. 

The results were these: it took them only nine minutes to fall asleep after consuming jasmine rice (high-GI) four hours before bed, about 15 minutes if they ate it one hour before shuteye and an average of 18 minutes when they had the long-grain, low-GI rice four hours prior to sleep.

The authors reported no change in sleep architecture and pointed out that adding more protein to the meal may change these results. 

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Carbohydrates, deep sleep, and REM sleep

Some studies link high-carb meals with a big reduction in deep sleep and an increase in REM sleep (for both, excessively high- and low- carb meals). 

REM percentage was shown to decrease in another research while deep sleep increased with a restriction in carbohydrates. These changes were observed in a short-term study and they may be linked to the sudden change in diet.

In obese people, a low-carb diet has shown an improvement in sleep disturbances and a normalization of sleep architecture, among other benefits.

Good carbs and bad carbs

“Good carbs” are the ones that are mixed with fiber (you can find them in oatmeal, lentils, beans, and fruit) whereas the “bad carbs” or simple carbs are found in sugar and processed foods.

Our body takes a long time to break down the complex carbohydrates. They help with serotonin increase, whereas too much sugar and processed carbs get absorbed rather quickly and result in frequent wakings. 

Mind your carbs before bedtime – they make the difference between sound sleep and interrupted restless sleep!

Figure 1. Complex carbs, fiber, and tryptophan help better sleep. Too much fat, sugar, and excessive protein intake are bad for your sleep quality. Source: GrowFit

Carbs, proteins, and sleep

You need the release of melatonin (also known as the darkness hormone) to make you sleepy and serotonin to trigger your sleep. 

One chemical is a precursor to both of them and it’s called tryptophan. Mostly found in protein-rich foods, tryptophan first has to cross the blood-brain barrier in order to interact with other chemicals. 

Tryptophan first needs to get through amino acids which make up this barrier and it can’t do this alone. The reason why it’s good to eat some carbs together with the protein is that the carbs will trigger the release of insulin which helps tryptophan cross the blood-brain barrier and make you fall asleep easily.

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Figure 2. Tryptophan crossing the blood-brain barrier with the help of carbs and being blocked without them. Source: BBC

Additional resources

  1. Effects of Diet on Sleep Quality https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5015038/
  2. Does what you eat matter to your sleep? https://thesleepdoctor.com/2016/06/27/eat-matter-sleep/
  3. Acute effects of the very low carbohydrate diet on sleep indices https://www.ncbi.nlm.nih.gov/pubmed/18681982
  4. Isocaloric diet changes and electroencephalographic sleep https://www.ncbi.nlm.nih.gov/pubmed/52766
  5. High-glycemic-index carbohydrate meals shorten sleep onset https://academic.oup.com/ajcn/article/85/2/426/4649589
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