Sleep problems are a major issue for Americans, and they can have a major effect on one’s mental health. The National Alliance on Mental Health claims that as many as half of insomnia cases are related to psychological stress, anxiety, or depression. The connection between sleep and depression is particularly strong. Writing in the journal Dialogues in Clinical Neuroscience, Nutt et al wrote, “The link between the two is so fundamental that some researchers have suggested that a diagnosis of depression in absence of sleep complaints should be made with caution.”
For some, sleep problems mean low sleep efficiency (SE), which is defined as spending less than 85 percent of the amount of time in bed asleep. For others, this means protracted sleep-onset latency, which is the amount of time it takes for one to fall asleep—which should, ideally, be between 15 and 20 minutes. For others still, it can mean a reduced amount of slow-wave sleep (SWS) and rapid eye movement (REM) sleep. These two stages of sleep are vital for memory consolidation and serve a restorative function for the body and brain.
More germane to the subject of this post, numerous studies have found that all these measurements of sleep quality and diet are interrelated. However, many of these studies are unclear about the direction of causality between the two. As the authors of a review recently published in the American Society for Nutrition noted, though these “studies reported a link between sleep and diet, it is unknown whether it is sleep that affects dietary intakes or dietary intakes that affect sleep.” In other words, it is not always clear if a diet high in fats and simple carbohydrates are causing sleep disturbances or if a lack of sleep is causing cravings for foods that are considered unhealthy due to their high sugar or fat content.
However, by examining the results of the data from previous studies, the paper’s authors were able to draw some tentative suppositions about the relationship between diet and sleep, though they were clear that more research and larger studies are needed to confirm their findings. Regardless, what they found is very intriguing.
Not So Sweet Dreams
Carbohydrates are a necessary part of any balanced diet. However, there are two distinct types of carbohydrates, and their effects on sleep appear to be night and day. On the one hand, there are simple carbohydrates that are quickly broken down by the body and give individuals bursts of energy that can be beneficial when one has low blood sugar. On the other hand, there are complex carbohydrates that take longer to be broken down by the body, provide fuel over long durations of time, and keep blood sugar levels more constant. The former typically comes in the form of sweets, which contain refined sugars, as well as bread and pasta that contain refined flours. The latter typically comes in the form of whole-grain bread and pasta. These types of carbohydrates also tend to have higher fiber content than their sugary brethren.
The review found that a diet that contains high amounts of simple carbohydrates is associated with poorer sleep quality. In a study that included 3,129 female workers in Japan ranging in age from 34 to 65 years, Katagiri et al discovered that the quality of sleep among participants who frequently consumed confectionery goods, processed noodles, and energy drinks was significantly worse than the quality of sleep among participants who consumed more vegetables and fish. The authors also found that skipping breakfast and eating irregularly were similarly associated with poorer sleep quality.
Conversely, a diet that relies more on complex carbohydrates than simple carbohydrates has been associated with improved sleep. Nisar et al, writing in the journal Cureus earlier this year, found that whole grains strongly influenced overall sleep quality among the 440 medical students who participated in the study. They offered several reasons as to why. First, whole grains contain large amounts of magnesium, which guides sleep-wake cycles by regulating melatonin and also serves as a muscle relaxant. Secondly, whole grains are known to increase levels of serotonin, a neurotransmitter that is believed to be necessary for sleep, and to lower levels of the stress hormone cortisol. Finally, whole grains allow tryptophan to cross the blood-brain barrier, which additionally boosts serotonin levels.
Whole grains also tend to contain more fiber than processed grains and sugars, which may impact sleep quality, as well. Writing in the Journal of Clinical Sleep Medicine, St. Onge et al found that higher fiber intake was associated with deeper and more restorative sleep. Conversely, “Low fiber and high saturated fat and sugar intake are associated with lighter, less restorative sleep with more arousals.”
In recent years, diets that encourage the intake of fat and protein over carbohydrates, such as the Atkins diet or the ketogenic diet, have become popular for individuals hoping to lose weight or to improve athletic performance. Such diets often have a negative impact on sleep efficiency initially, but can improve SE in the long term.
Additionally, studies have shown that low carbohydrate diet changes sleep architecture, largely because of changes to nocturnal energy metabolism. Afgahi et al found that the percentage of REM sleep experienced throughout the night declined and the amount of SWS sleep increased with such a diet. Meanwhile, Lindseth et al reported in 2013 that high-protein/low-carbohydrate diets resulted in fewer wake episodes, and three years later claimed that diets high in fat resulted in improved sleep when compared with other diets after a separate study.
While there are numerous limitations in these studies, the findings do suggest that replacing carbohydrates with healthy proteins and fats may increase the ratio of deep sleep to REM sleep. However, these studies have numerous limitations, largely because they only lasted a short duration. More research needs to be conducted to better understand the long-term effects of low-carbohydrate diets on sleep architecture.
While these findings do not necessarily give us a roadmap to discover the best diet for sleep, it is clear that refined sugars and simple carbohydrates, particularly when consumed within the hours before bedtime, are not associated with healthy sleep. Consequently, if one is hoping to make changes to their diet to sleep better, one should not go to extremes by foregoing entire groups of macronutrients or becoming a strict vegan. Small changes, such as eating more whole foods (whether they are fruits, vegetables, and whole grains or vegetables, proteins, and healthy fats) and avoiding confections, processed starches, and sugary sodas may improve sleep, as well as mental health.
Dr. Ahmad reports no conflict of interest. He is not a speaker, advisor, or consultant and has no financial or commercial relationship with any biopharmaceutical entity whose product/device may have been mentioned in this article.