All of these sleep strategies have merit, according to a new study supported by the Australian Rugby Foundation and conducted by scientists at the University of Canberra.
“The ingestion of carbohydrates to improve sleep parameters is inconclusive, although foods with a high glycemic index seem to have small benefits. Tart cherry juice may promote the amount of sleep, herbal supplements may improve sleep quality, while kiwi fruit and protein interventions improve both sleep quality and quantity,”wrote the researchers in the journal Nutrients.
Despite evidence confirming the importance of sleep for recovery and reduction of fatigue-related injuries, elite athletes seem to experience more sleep disturbancesthan the general population. This is believed to be due to a combination of factors including nighttime competitions, training schedules and travel.
It is well established that nutrition plays a vital role in athlete performance and recovery, but the science behind the role of specific foods, macronutrients and micronutrients in the sleep-wake cycle is in its infancy.
The Australian researchers therefore carried out a literature review to study the nutritional strategies that can be used to improve sleep quality. Given the limited volume of studies in the athlete population (four in total), the inclusion criteria were expanded to include studies that reported outcomes of nutritional interventions to improve sleep in otherwise adults. in good health. A total of 20 studies were included in the review.
The nutritional interventions studied in these studies were: carbohydrates, proteins, tart cherry juice, glycine, L-serine, beet juice, kiwifruit, GABA (an amino acid produced by natural fermentation) and a herbal sleep supplement. However, not all of them produced conclusive results.
Meals High in GI Carbs Promote Sleep
Carbohydrates are the most studied macronutrient in relation to sleep. Although evidence from studies involving athletes is limited, studies in healthy populations are more definitive, with consistent reports of improved sleep following high glycemic index (GI) carbohydrates. Overall, in three studies, consuming high-GI carbohydrates increased total sleep time by eight to 62 minutes and reduced the time from bedtime to falling asleep by 6 to 19 minutes.
In a studyParticularly important for athletes, researchers provided young men with a low- or high-GI meal immediately following an evening sprint session. The high GI meal significantly improved total sleep time, sleep onset latency (time from bedtime to falling asleep), sleep efficiency (ratio of sleep time to time in bed), and waking after falling asleep (the time awake after initial falling asleep).
This effect is thought to be due to an increase in the plasma ratio of tryptophan to large neutral amino acids.
“Tryptophan is an essential amino acid and serves as a precursor to the synthesis of serotonin and melatonin, two important regulators of sleep. By increasing the ratio, tryptophan can more easily cross the blood-brain barrier, leading to an increase in serotonin synthesis and then a downstream increase in melatonin secretion,” explained the researchers.
Preliminary evidence for proteins
Two studies explored the effects of protein on sleep. Both used the whey protein isolate alpha-lactalbumin, which is reportedhave the highest natural tryptophan level of any protein food source. In aAmong the studies, pre-sleep protein supplementation increased total sleep time by 55 minutes, alongside a 7% increase in sleep efficiency. However, in the other study, which was carried out on a small sample of cyclists, no effect was observed.
“Although there is preliminary evidence supporting the effectiveness of alpha-lactalbumin in improving sleep, further well-designed studies are needed to confirm its effectiveness,” noted the authors.
Tart cherry juice
The two tart cherry juice studies were both done in general population cohorts. They showed an increase in total sleep time from 29 to 39 minutes, modest improvements in sleep efficiency (2.7 to 3.7%), and small reductions in sleep onset latency (four to nine minutes) and waking up after falling asleep (17 minutes).
The explanation for this effect could be that tart cherries contain around 13 ng of melatonin per kg, which is essential for the sleep-wake cycle in humans. The high antioxidant content of cherries may also improve sleep by reducing oxidative stress.
“Further research is needed to evaluate the use of tart cherry juice in an athletic population, including its effects on sleep and physiological recovery,” concluded the researchers.
Kiwi, GABA and glycine
There are a variety of other nutritional strategies that have been explored for their ability to improve sleep, including kiwifruit, GABA, and glycine.
The improvement in sleep was reported in poor sleepers who ingested two kiwifruit one hour before bed over a four-week intervention period.
This could be due to the presence of serotonin (a known sleep-promoting hormone) and/or high levels of folate in kiwi fruit. Folate deficiency has been linked to insomnia and restless leg syndrome.
GABA ingestion has also made an improvementsin the sleep quality of poor sleepers. GABA is an inhibitory neurotransmitter and its receptors in the central nervous system are often targeted by pharmacological agents such as benzodiazepines for the treatment of insomnia.
Glycine is another inhibitory neurotransmitter that has been linked to improved sleep quality, along with L-serine, a precursor to glycine.
“While further evidence of the efficacy of glycine and L-serine in athletic populations is needed, these results suggest that both proteins may offer athletes who are dissatisfied with sleep issues or face restricted sleep. situational sleep, a way to improve their sleep”,wrote the researchers.
Sleep Improvement Guidelines
The researchers concluded that the following sleep improvement strategies can be derived from studies published to date:
- Consume a high GI carbohydrate meal 2-4 hours before bedtime
- Incorporate Tart Cherry Juice Concentrate into an athlete’s daily routine when sleep may be impaired: 1 x 30ml upon waking and 1 x 30ml before the evening meal.
- Consume 20-40g of a tryptophan-rich protein source, such as alpha-lactalbumin-enriched whey protein, 2 hours before bedtime.
- Regular consumption of kiwis one hour before bedtime.
- Glycine at a dose of 3g taken before bedtime.
“Nutritional Interventions to Improve Sleep in Team Sports Athletes: A Narrative Review”
Authors: Gratwicke M, Miles KH, Pyne DB, Pumpa KL, Clark B