Diet Promoting a Good Night's Rest

Sleep is a state of activity that occurs periodically and spontaneously, and during which the perception of external signals is interrupted and no active tasks are performed. It is a behavior that isolates oneself from the environment. It is a natural necessity of the human being and takes up about 1/3 of his life. Currently, the standard amount of sleep per week is only 6-6.5 hours per day. Limiting sleep to 6 hours for 4 days affects cognitive functions, performance, mood, glucose metabolism, appetite regulation, and immune function. It is recommended that adults should sleep 7–9 hours per day and teenagers 8.5–9.5 hours per day. From the perspective of sleep physiology, we can divide sleep into two phases: REM and NREM. The REM phase is associated with the occurrence of dreams, while the NREM phase is deep sleep, during which the body rests. Standard nighttime sleep consists of cyclical changes in NREM and REM phases, which repeat 4–5 times per night every 90 minutes. After each cycle, sleep usually becomes lighter and there are short-term awakenings. In the following cycles, the NREM phase shortens, while the REM phase lengthens. Sleep during the first three cycles covers more than 90% of the need for deep sleep. It is important to note that the cyclical phase changes of sleep depend on the mutual influence of serotonergic and noradrenergic neurons, called REM-off (not active in the REM phase), and cholinergic REM-on neurons (active in the REM phase). In addition to the neurotransmitters mentioned above, we can also distinguish several others related to the sleep cycle, such as 5-HT, gamma-aminobutyric acid (GABA), orexin, melatonin, galanin, norepinephrine, and histamine. Some nutritional interventions can affect the functioning of the mentioned neurotransmitters and thus also the quality of sleep.

Nutritional components can impact the process of synthesis and the function of certain neurotransmitters, including 5-HT (serotonin receptors). Figure 1 illustrates the effect of diet on the central nervous system by the production of 5-HT and melatonin. The synthesis of 5-HT is dependent on the availability of an L-tryptophan (Trp) amino acid precursor in the brain. Trp is transported through the blood-brain barrier, which is also utilized by other large neutral amino acids (LNAA) in the bloodstream. Therefore, the ratio of Trp to LNAA in the blood is crucial for the transport of Trp to the brain. Consuming larger amounts of LNAA can inhibit the absorption of tryptophan. However, consuming carbohydrates increases the transport of Trp to the brain through the stimulation of insulin, and the circulating LNAA amino acids are taken up by the skeletal muscles, resulting in an increase in free Trp, which in turn improves sleep quality. Source: Halson S. L., Sleep in Elite Athletes and Nutritional Interventions to Enhance Sleep, "Sports Medicine" 2014, 44, 13–23.

The investigation conducted by J. M. Porter and J. A. Horne focused on the examination of the amount of carbohydrates consumed 45 minutes before bedtime. This was achieved by administering large doses of carbohydrates (130 g), smaller doses (47 g), or completely omitting carbohydrates from the meal. The study revealed that a meal containing a high dose of carbohydrates contributed to prolonging the REM phase, shortening light sleep, and reducing insomnia symptoms. Products with a high glycemic index such as white rice, pasta, rice cakes, and bread can improve sleep quality if consumed in the evening. However, it is important to note that such meals should be consumed no later than an hour before bedtime.

An addition of 1 g of L-tryptophan may contribute to the enhancement of sleep onset and subjectively assessed sleep quality. When devising meal plans, it is prudent to pay attention to selected foods with high L-tryptophan content, such as chicken eggs, cod, offal, soybeans, pumpkin seeds, mozzarella cheese, salmon, milk, soy protein isolate, and poultry.

The biological function of melatonin has been the subject of extensive research – its therapeutic effects and health benefits have been demonstrated. It can regulate the daily cycle, alleviate symptoms of jet lag syndrome, counteract insomnia, and also affect a number of bodily functions, etc. It has anti-aging and anti-inflammatory effects. Melatonin is found in many food products, but its quantity significantly varies. It depends on the environment and breeding conditions, temperature, and time spent in the sun. In animal products, the highest concentrations of melatonin are observed in eggs and fish. Melatonin is also found in breast milk and the milk of other mammals. It can also be found in fruits such as cherries, grapes, and strawberries. In one study, an increase in the level of exogenous melatonin was observed after consuming cherry juice, and after two weeks of consumption, an improvement in the symptoms of insomnia was demonstrated compared to placebo. The administration of the juice also resulted in an improvement in sleep quality and an extension of its duration. It is believed that cherry juice, due to its antioxidant effect, can influence the sleep cycle by affecting cytokines associated with poor sleep quality.

Valerian herb is a plant that connects with GABA receptors type A and potentially produces a calming effect by reducing the stimulation of the nervous system. A review of studies on the effectiveness of valerian herb has shown a subjective improvement in sleep quality. However, supplementation with this ingredient can lead to unwanted side effects, such as headaches, drowsiness, allergic reactions. Furthermore, GABA can influence the release of growth hormone. It is worth noting that valerian herb is a common ingredient in dietary supplements supporting sleep and relaxation. GABA is also present in foods such as fermented foods, kefir, sauerkraut, and pickles.

Individuals who lead active lifestyles should focus on maintaining proper sleep hygiene in order to maximize sleep quality and duration. This includes ensuring regular sleep patterns, allocating appropriate time for sleep, avoiding excessively short or long sleep durations, sleeping at around 18°C, wearing appropriate clothing, and avoiding use of phones, televisions, and computers for 30 minutes prior to sleep. Various dietary practices may impact sleep quality. Maintaining a balanced diet and avoiding low-carbohydrate diets, which can shorten sleep duration, is important. Excessive fat in the diet can have negative effects on overall sleep quality and duration. Inadequate energy intake can also disrupt sleep quality. Introducing meals rich in tryptophan (1 g) to the diet may improve sleep quality and extend sleep duration - this can be achieved through consuming approximately 300 g of turkey or around 200 g of pumpkin seeds. Introducing supplements containing valerian may have positive effects, but only high-quality products from trusted sources should be used. Athletes, particularly professional athletes, should be aware of the potential risks associated with contamination in low-quality supplements. The introduction of any potential pharmacological treatment should be discussed with a specialist physician.