The year is now in full swing, with most of us back into the daily grind of work, school, university and endless lists of commitments. With these demands comes inevitable stress and its domino effect into many other aspects of our lives. Our sleep is usually one of the first to suffer, so scientific wellness companies have capitalised on this. Dietary sleeping aids such as Moon Juice’s Dream Dust, The Goodnight Co’s Supplement Powder and The Beauty Chef’s Inner Beauty Powder are being increasingly marketed to us through social media platforms and health gurus. The biggest shocker is the new range of sleep-promoting ice-creams by Nightfood, which has just launched in the US so it’s only a matter of time until something similar reaches Australia. However, our consumption of certain nutrients (or lack thereof) isn’t the only dietary choice affecting our sleep. There are a couple of other factors worth taking a note of, which we’ll explore below.
When You Eat
Sleep and alertness are influenced by your circadian rhythm, which is essentially a 24-hour biological cycle of bodily functions regulated by the hypothalamus. The steroid hormone, cortisol, regulates the sleep-wake cycle of your circadian rhythm and is highly influenced by stress and dietary patterns. Your cortisol levels are normally higher in the morning and lower in the evening, enabling you to start the day alert and slowly wind down through to the night. However, aside from acute stress, when and how often you eat can significantly alter your cortisol levels outside of the norm. This is because blood sugar responses can affect cortisol levels. If you eat a high GI meal that spikes your blood glucose, your cortisol levels may be elevated up to 5 hours postprandially- not great news for you and your sleep if you eat too close to bedtime! Similarly, skipping meals or falling close to the hypoglycaemic range (i.e. a blood sugar level <4 mmol/L) can also elevate your cortisol levels as your body deals with physiological stress. Such deviations to your cortisol levels subsequently affect your circadian rhythm and ultimately your sleep-wake cycle.
Similarly, when you eat certain foods can also affect the quality of your sleep. The main culprits for most people are alcohol, caffeine and spicy foods. Alcohol, although a sedative and a relaxing post-dinner ritual for many, has been scientifically proven to increase sleep latency (i.e. the time it takes to fall asleep) and reduce total sleep time. Caffeine is not only a ‘pick-me-up’ for many but is inherently interwoven into social norms as evidenced by global coffee culture. Energy drinks, chocolate and tea also contain caffeine. This widespread consumption combined with highly variable individual sensitivities to caffeine, makes it a challenging substance to moderate. As such, the most sensible decision for good sleep is to limit intake of high caffeine foods such as coffee and energy drinks to no later than lunch time. Spicy foods such as chilli curries, consumed too close to bedtime, can cause oesophageal reflux and other gastrointestinal symptoms which inevitably make it difficult for you to wind down and sleep. This is one of several reasons why you should aim to have dinner 2-3 hours before bed.
Your Overall Diet
Traditional dietary remedies for sleeplessness such as warm milk, turkey dinners, tart cherry juice and eating kiwi fruit are loosely based on scientific evidence. Literature reviews have conjectured that it isn’t really the specific nutrients in those remedies that aid sleeplessness, but rather a multitude of other factors such as vitamin deficiencies, the interaction between different food sources and the placebo effect just to name a few.
For instance, after a bout of insomnia you may have been advised to have a glass of warm milk. Such advice is likely to have come about from the fact that dairy contains the amino acid tryptophan. Tryptophan is needed to synthesise the neurotransmitter serotonin, which is the precursor to melatonin. Melatonin is essentially the ‘sleep hormone’ that regulates the sleep-wake cycle of your circadian rhythm. As tryptophan is an essential amino acid that can’t be synthesised by the body, it would make sense to increase your levels before bedtime, right? Well, aside from the fact that it takes about an hour for the tryptophan in a glass of milk to reach the blood-brain barrier, several studies have shown that a glass of milk doesn’t contain sufficient tryptophan to induce sleepiness. In reality, there isn’t a magic dose of amino acids for sleep, but rather a recommended dietary intake (RDI) of 0.84 g/kg of overall protein for men and 0.75 g/kg for women aged 19-70 years old. Hitting these daily targets by consuming a wide variety of protein sources will ensure you aren’t deficient in any amino acid, and subsequently will promote healthy metabolic functioning as well as repair, maintenance and growth of tissue. Moreover, increasing the bioavailability of tryptophan requires synergy with magnesium, B-vitamins and complex carbohydrates. So why does a glass of warm milk taken before bed induce sleepiness in many individuals? The answer most likely lies in the ritualistic or soothing effect that a warm beverage can have on us after a long, tiring day.
A recent literature review also found correlations between low-fat diets and the feeling of good sleep. Individuals on short-term high-fat diets experienced reduced sleep efficiency (i.e. time spent asleep), higher arousal incidences and reduced slow-wave sleep (i.e. deep sleep associated with restorative functions). While such studies demonstrated correlation rather than causation, they further solidify the basic tenets of good nutrition.
The Bottom Line
‘Good sleep’ is challenging to scientifically quantify and is highly variable between individuals. As such, it is difficult to pinpoint the exact nutrients each person needs on any given day to have sufficient restful sleep. So rather than holding your nose and downing dietary sleep concoctions, aim to eat a varied diet full of good quality proteins, fruits and veggies, carbohydrates and dairy to hit all your required micro and macronutrients. Avoid caffeinated food and drinks after lunch time and try to eat 2-3 hours before bedtime. Swap post-dinner alcoholic drinks with another relaxing ritual or aim to stop drinking 2-3 hours before you want to sleep. Finally, to get the highest chances at optimal sleep, combine good dietary choices with good sleep hygiene, stress management and an overall healthy lifestyle.
Nadia is a final year Bachelor of Science student, majoring in Nutrition and Metabolism at the University of Sydney. Her passion for dietetics, health and wellbeing began as a young foodie with a love for helping people in need, and grew into a dream to become a dietitian.
As an aspiring health professional, Nadia’s long-term goal is to complete a Masters of Nutrition and Dietetics and gain a wealth of experience in all aspects of dietetics – from fertility and gut disorders to mental health. In the meantime, Nadia can be found brunching with friends, binge-watching chick flicks with her Mum and sisters, soaking up the sun between classes and avidly reading fiction and non-fiction books.