Carbohydrate and sleep: An evaluation of putative mechanisms

Abstract

Sleep problems are extremely common in industrialized countries and the possibility that diet might be used to improve sleep has been considered. The topic has been reviewed many times, resulting in the frequent suggestion that carbohydrate increases the uptake of tryptophan by the brain, where it is metabolized into serotonin and melatonin, with the suggestion that this improves sleep. An alternative mechanism was proposed based on animal literature that has been largely ignored by those considering diet and sleep. The hypothesis was that, as in the hypothalamus there are glucose-sensing neurons associated with the sleep-wake cycle, we should consider the impact of carbohydrate-induced changes in the level of blood glucose. A meta-analysis found that after consuming a lower amount of carbohydrate, more time was spent in slow-wave sleep (SWS) and less in rapid-eye-movement sleep. As the credibility of alternative mechanisms has tended not to have been critically evaluated, they were considered by examining their biochemical, nutritional, and pharmacological plausibility. Although high carbohydrate consumption can increase the uptake of tryptophan by the brain, it only occurs with such low levels of protein that the mechanism is not relevant to a normal diet. After entering the brain tryptophan is converted to serotonin, a neurotransmitter known to influence so many different aspects of sleep and wakefulness, that it is not reasonable to expect a uniform improvement in sleep. Some serotonin is converted to melatonin, although the exogenous dose of melatonin needed to influence sleep cannot be credibly provided by the diet. This review was registered in the International Prospective Register of Systematic Reviews (CRD42020223560).

Understanding the experiences of ketogenic metabolic therapy for people living with varying levels of depressive symptoms: a thematic analysis

“…Sleep quality also improved which is to be expected as research suggests that following a higher carbohydrate diet negatively impacts sleep by increasing sleep length but reducing its quality by spending more time in rapid-eye-movement (REM) compared to slow-wave sleep (SWS) ( 25 ). According to a systematic review, individuals following a low carbohydrate diet tend to spend more time in SWS and experience an increase in the duration of deep sleep ( 26 ).…”

Association of Evening Eating with Sleep Quality and Insomnia among Adults in a Brazilian National Survey

“…46 Although further research should be performed to clarify the causality and underlying mechanisms to explain the relationship between carbohydrate consumption and sleep, the most commonly proposed mechanisms refer to changes in the levels of brain tryptophan, serotonin, or melatonin. 47 The influence of meal composition, both in terms of macro and micronutrients, meal size, and meal timing, must be explored in future studies to improve our understanding of the relationship between diet and sleep.…”

“…Although further research should be performed to clarify the causality and underlying mechanisms to explain the relationship between carbohydrate consumption and sleep, the most commonly proposed mechanisms refer to changes in the levels of brain tryptophan, serotonin, or melatonin. 47…”

Mediterranean Diet and Sleep Features: A Systematic Review of Current Evidence

“…The neurophysiological mechanisms behind such observations are still under investigation: one can hypothesize that carbohydrates may affect tryptophan content in the central nervous system, which is needed to synthetize serotonin, also important for melatonin production [ 51 ]. Another potential mechanism relies on the hypothesis that glucose-sensing neurons in the hypothalamus may affect hypothalamus [ 52 ].…”