At ZOE, we understand the importance of sleep. We also understand that there are links between sleep quality and how your body responds to carbs.
For instance, our research has shown that after a bad night’s sleep, you're more likely to have big blood sugar spikes after breakfast the next day.
The links between food and sleep run deep. Research has also shown that people who generally sleep fewer than 7 hours each night tend to eat more calories.
ZOE collaborator Raphael Vallat, Ph.D., is a neuroscientist and sleep researcher in the Center for Human Sleep Science at the University of California, Berkeley.
He told us that “while there are many epidemiological studies showing a clear association between food intake and sleep, there is a lack of studies directly addressing directionality.”
In other words, although there is good evidence that sleep deprivation makes us more likely to reach for the snacks, fewer studies have asked whether carbs directly affect sleep.
Here, we’ll look at the evidence so far.
Not all carbohydrates are equal
We should mention straight away that carbohydrates come in many forms. At the healthy end of the spectrum, we have fiber.
Found in fresh fruits, vegetables, nuts, and seeds, fiber feeds your gut bacteria. It also aids digestion and is associated with better gut health. Additionally, complex carbs, like those found in whole grains, are a good source of energy.
At the less healthy end of the carb spectrum, we have refined sugars — the type you find in sugar-sweetened sodas and ultra-processed foods.
These sugars cause spikes in blood sugar and are linked to an increased risk of obesity, heart disease, tooth decay, and more.
Here’s a quick guide to some of the common terms for carbs:
Fiber: A type of carb your body can't digest. Found in fruit and veg, fiber is important for health.
Complex carbs: Long strings of sugar molecules that are found in vegetables and whole grains. They're a good source of energy.
Simple carbs: Sugars like glucose, fructose, and sucrose that your cells can absorb quickly. You can find these in fruit and milk, for example.
Refined or processed carbs: These are sugars or grains that have been refined, removing most nutrients. These are found in white pasta, white rice, white bread, and table sugar.
Added sugars: Manufacturers add these to foods during processing. They tend to be simple carbs and don't add any nutritional value.
We’ll touch on both ends of the scale, but we’ll mostly be looking at added sugars.
Carbs and disrupted sleep
One of the challenging aspects of studying nutrition is that everyone has different dietary habits, and those habits can change from day to day.
Unless you monitor someone’s meals very closely, it’s difficult to determine between cause and effect: Do they have a higher sugar intake because they are tired, or are they sleeping poorly because of the added sugars?
To try and solve this conundrum, some scientists have run small studies where they carefully monitor and control participants’ food intake.
For instance, one group of researchers fed 26 participants a fixed diet while they stayed in a sleep research facility for 6 days.
The scientists found that when participants ate higher levels of saturated fat and lower levels of fiber, they slept more lightly than when they ate their standard diet.
They also found that when participants ate more sugar or other non-fiber carbohydrates, participants woke up more regularly throughout the night. Overall, the authors conclude:
“[I]t is possible that a diet rich in fiber, with reduced intake of sugars and other non-fiber carbohydrates, may be a useful tool to improve sleep depth and architecture in individuals with poor sleep.”
Other scientists have also shown that consuming more non-fiber carbs can increase the number of times someone wakes during the night.
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Another study looked at this question from the opposite direction. They wanted to know whether eating a very low-carb diet for 2 days might influence sleep. To investigate, they recruited 14 healthy men aged 18–35.
They found that consuming very little carbohydrate reduced the amount of rapid eye movement (REM, or dream) sleep and increased the amount of deeper slow-wave sleep.
This suggests that low-carb diets, such as the keto diet, might influence sleep. But it’s not clear whether this change in sleep is meaningful for health or if it would persist longer than 2 days.
Carbs and insomnia
One group of researchers investigated insomnia in postmenopausal women. Could carbohydrates be involved?
The authors of the study, who had access to data from tens of thousands people, concluded:
“Higher intakes of dietary added sugars, starch, and non-whole/refined grains were each associated with higher odds of incident insomnia.”
They also found that higher fruit, vegetable, and fiber intake were associated with lower odds of insomnia.
So again, different types of carbs had opposite effects: Fiber was associated with reduced insomnia, and quick-release sugars were associated with increased insomnia.
This study, however, can’t prove cause and effect. As we’ve mentioned, it might be that sleep-deprived people with insomnia are simply more likely to choose energy-dense foods.
Soda and sleep
In line with the insomnia research above, a number of studies have found links between soda consumption and poor sleep.
For instance, an Iranian study of almost 400 adults found that sugar-sweetened beverages were associated with reduced sleep quality.
Similarly, some Korean research concluded that children who drank more soda and sweet drinks slept for fewer hours each night.
However, these studies are mostly observational so, again, we can’t tell whether soda disrupts sleep or whether disrupted sleep increases the urge for soda.
Do carbs make you sleepy?
As we’ve seen, there’s conflicting evidence that carbs might interfere with a good night’s sleep. But there’s also some evidence that carbs might make you more tired and promote sleep.
A study — although from the 1980s — shows this effect. Scientists gave participants either a large carbohydrate dose in supplement form or a placebo.
Compared with the placebo group, participants who took the carb supplement woke up less often during the night, had more REM sleep, and had less light sleep.
Another small trial involving 12 healthy men tested the effects of a high-glycemic index meal on sleep compared with a low-glycemic index meal.
Scientists sometimes use the glycemic index to help assess how quickly a food might affect blood sugar levels.
For instance, white rice is broken down quickly in your gut and, for some people, can cause blood sugar levels to rise rapidly. So, white rice has a high glycemic index.
At the other end of the scale, foods like vegetables and nuts tend to break down much slower, and sugar is released into the bloodstream more gradually. Therefore, veggies and nuts have a low glycemic index.
It’s worth noting that everyone’s body responds differently to carbs. Even identical twins could have different blood sugar responses to the same high-glycemic index meal.
The researchers also investigated whether timing made a difference — participants ate the meal either 1 or 4 hours before bed.
The scientists showed that eating a high-glycemic-index meal 4 hours before bed made it easier for participants to drop off to sleep — but not so much when eaten 1 hour before.
However, they didn’t identify any other changes to the participants' sleep, such as how long they slept for.
Why might carbs influence sleep?
Scientists don’t know for sure why carbs might influence sleep, but they have some theories.
One idea is that carbs might tinker with your circadian rhythms — your 24-hour body clock that oversees physical and mental changes throughout the day.
Studies have shown that a carbohydrate-rich evening meal delays your body clock and reduces the release of melatonin — a hormone that helps control the sleep-wake cycle.
The authors of the insomnia study think that spikes in blood sugar might help explain why certain carbs hinder sleep. They explain that blood sugar spikes prompt a spike in insulin release.
As insulin quickly moves sugar away from the blood and into cells, it can cause a blood sugar crash. And if glucose levels in the brain drop too low, it can trigger the release of hormones, including adrenaline, to try to bring glucose back to safe levels.
The effects of these hormonal countermeasures can be enough to rouse someone from their sleep.
Also, as Dr. Vallat explained to us, sugar spikes “may elevate your body temperature and heart rate and thus prevent you from having a deep, restorative sleep.”
The authors of the insomnia study also explain that diets rich in high glycemic index foods can trigger inflammation.
During inflammation, the body releases anti-inflammatory cytokines, which are important cell signaling proteins. Some of these compounds can inhibit sleep.
Dr. Vallat also outlined a way that carbs might increase feelings of sleepiness. He explains that eating carbs promotes tryptophan entry into the brain.
In response to increased tryptophan, the brain produces more serotonin, which promotes sleep.
All in all, it does seem that carbs might influence sleep, but the evidence is patchy and sometimes contradictory.
Studies that closely monitor participants’ food intake and sleep are challenging and expensive to run. Because of this, they almost always involve small numbers of people and run for just a few days.
Scientists will need to conduct more long-term research to determine causality and further establish how and why sugar impacts sleep.
One factor that muddies the waters is that we are all individuals. ZOE’s research has shown that everyone responds differently to food. For instance, even identical twins can have different blood sugar responses to the same meal.
And, of course, there is more to your diet than carbs. It’s the whole diet that counts, including when you eat, what other nutrients are in the food, and what foods you eat together.
Understanding how your body responds to food can help you choose the right foods to suit your body and promote your long-term health.
When you join ZOE, we measure your blood sugar and blood fat responses to food — both of which are linked to health outcomes. We also analyze your gut microbiome.
Using this detailed information, we provide personalized nutrition advice for your body.
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