Sleep is essential to promoting optimal health and performance, but there are a number of factors that affect sleep quality and quantity, including dietary intake. The consumption of food has a direct effect on the neurotransmitters that regulate the sleep cycle to enhance or worsen sleep.
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Some key findings of nutrition and sleep include:
- High glycemic index (GI) food may help to improve sleep when consumed more than an hour before bedtime.
- High carbohydrate diets may cause shorter sleep latencies whereas high protein diets are associated with higher sleep quality.
- Solid meals may be more beneficial than liquid meals to promote sleep.
Role of neurotransmitters
The neurotransmitters that are involved in the regulation of the sleep-wake cycle include serotonin, gamma-aminobutyric acid (GABA), orexin, melanin-concentrating hormone, cholinergic, galanin, noradrenaline, and histamine.
Several foods have an impact on these neurotransmitters in the body and, as a result, can affect the sleep-wake cycle. This may occur by dietary precursors altering the rate of synthesis and function of neurotransmitters in the body.
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The consumption of carbohydrates and its effect on sleep quantity and quality has been considered in several scientific studies.
It has been suggested that the consumption of a meal high in carbohydrates shortly before bedtime leads to an increase in rapid eye movement (REM) sleep, with a reduction in light sleep and wakefulness. However, it remains unclear if this effect is due to the calories or the carbohydrates in the meal consumed.
Additionally, some research has indicated an effect on the type of meal consumed. For example, solid meals were associated with improved sleep onset latency, whereas a liquid meal was slightly better than drinking water. This did not appear to have an effect on the quality of sleep, however.
The GI of food may also have an impact on sleep. High GI meals have been linked to enhanced sleep onset latency when compared to low GI meals. Additionally, consumption of the high GI meal was found to be more effective 4 hours before bedtime, rather than 1 hour before.
Diets high in protein have been associated with increased restlessness during sleep, whereas low protein intake is linked to reduced slow-wave sleep. Despite this, the total sleep time was unchanged, and the practical applications of these findings are unclear.
Most diets are either high in protein, high in carbohydrates, or high in fat. The effect of the different meal compositions on the quality and quantity of sleep has been studied.
High carbohydrate diets were associated with shortened sleep onset latencies, whereas diets high in protein were linked to few episodes of wakefulness. Interestingly, high fat diets did not appear to have a marked effect on sleep, but may reduce the overall quantity of sleep.
Tryptophan plays an important role in sleep, as it is a precursor in the synthesis of serotonin in the body. Several studies have investigated the effect of tryptophan supplementation on sleep quality and quantity. The results of these suggested improvements in sleep latency and quality. Dietary sources of tryptophan include turkey and pumpkin seeds.
Melatonin is intricately involved in the circadian rhythms of the body and is thought to have a sedative or hypnotic effect on the body. Melatonin may help to improve sleep onset latency and appears to be safe to use, but conclusive evidence is lacking. Dietary sources of melatonin include tart cherry juice.
Valerian is a herb that binds to GABA receptors to produce a calming effect on the body. Supplementation of valerian may help to improve sleep quality but is not thought to lengthen total sleep time.