When was the last time you had a good night’s sleep, and woke up feeling fully restored and ready to take on the day with gusto? If it was last night, and most nights before that, congratulations. Pass this article on to someone who needs it!
But if you’re one of the 40% of Australian males and 50% of Australian females who admitted to “waking feeling unrefreshed” in the 2016 Sleep Health Survey of Australian Adults, keep reading. You have more control over how well you sleep, and how you feel when you wake up, than you know.
Getting a good night’s sleep on a consistent basis isn’t just one of life’s great pleasures. It’s crucial for good health. People who sleep less than 6-7 hours on average per night have an increased risk for
- Obesity
- Type 2 diabetes
- Hypertension (high blood pressure) and heart disease
- Reduced natural immune function, which increases the risk of infections and possibly cancer
- Impaired cognitive function and mental well-being, including disturbances in mood, thinking, concentration, memory, learning, vigilance and reaction times
- Motor vehicle and workplace accidents
- Decreased workplace performance and productivity.
It’s long been known that sleep deprivation adversely affects our metabolism. After just 5 nights of only being allowed to sleep for 4 hours, healthy young men were found to have impaired glucose metabolism (decreased glucose tolerance and insulin sensitivity) and increased adrenal reactivity, indicating a heightened stress response.
Furthermore, sleep deprivation causes changes in appetite-regulating hormones (decreased leptin and elevated ghrelin) that drive increased hunger, especially for energy-dense foods.
But does the relationship between diet and sleep also work back the other way – that is, does what we eat impact on our sleep? That’s what a team of researchers from the New York Obesity Research Center sought to find out, in a study that assessed the effect of specific components of diet, including fibre, fat, sugar and starch, on the quality of sleep.
The study participants, who were screened to exclude those with pre-existing sleep disorders, excessive daytime sleepiness, and poor sleep quality, agreed to live in a sleep research facility for 2 periods of 6 days each. The meals they ate during their stays were analysed for macronutrient content, and each night, they were hooked up to a polysomnographic (PSG) monitor which tracked their progression through the cycles and stages of sleep.
It may not seem like it, but a lot happens when we’re asleep! Using the PSG, the researchers were able to determine:
- Total sleep time (TST) – how long participants spent asleep each night;
- Sleep onset latency (SOL) – how long they took to fall asleep when they went to bed;
- Number of arousals – how many times they woke up out of sleep each night (whether or not they were awake long enough to remember it); and
- The amounts of stage 1 sleep, stage 2 sleep, slow wave sleep (SWS), and rapid eye movement (REM) sleep.
Briefly, SWS (which comprises stage 3 and stage 4 sleep) is a time of rest and repair for the brain and body:
- Sympathetic neural activity (the fear-fight-flight arm of the nervous system) quiets down while parasympathetic activity (the rest-digest-heal arm) ramps up.
- Secretion of growth hormone, which stimulates actual growth in children, and healing and repair of muscles, bones and other vital tissues in adults, hits its peak.
- Certain types of memory are consolidated, meaning that adequate SWS is necessary for leaning.
On the other hand, REM sleep resembles wakefulness more than sleep, with brain neurons firing at the same intensity as when we’re awake, and heart rate, blood pressure and breathing rate becoming irregular. Our most vivid dreams occur during REM sleep. This phase of sleep also appears to be important for the consolidation of certain types of memory, as well as ‘unlearning’ unimportant memories.
So what did the researchers find? In a nutshell, on days when people ate more fibre, they feel asleep faster and slept more deeply:
“Fiber intake is associated with deeper, more restorative sleep.”
On the other hand, when they ate more saturated fat and refined carbohydrates, they spent less time in restorative SWS and woke more often during the night:
“Higher saturated fat intake throughout the day was associated with a lesser amount of SWS at night… A greater intake of saturated fat and lower intake of fiber were associated with a lighter, less deep sleep profile. Additionally, increased intake of both sugar and non-sugar/non-fiber carbohydrates was associated with more nocturnal arousals during sleep.”
Although the researchers couldn’t say with certainty just how fat, fibre and refined carbohydrates affect our sleep (personally, I suspect that the effect is mediated at least partly through the impact of the foods we eat on our gut microbiota), the implications for people who suffer from unrefreshing sleep, daytime drowsiness and irritability are clear: eating more whole plant foods and less junk food and animals products may be as good for your sleep as for your weight, metabolic and heart health.
But there are also implications for people who have jumped on the ketogenic diet bandwagon, as the researchers noted, with evident concern:
“A high-fat, low-carbohydrate ketogenic diet has been promoted as a therapeutic option for several neurological disorders including Alzheimer disease, Parkinson disease, and epilepsy.38 These dietary alterations may be associated with changes in nocturnal sleep, and indeed, insomnia has been reported in response to a ketogenic diet.39 Therefore, increasing our understanding of the impact of dietary intake on nocturnal sleep will have many important and practical ramifications for public health.”
Isn’t it fascinating that scientists keep uncovering new ways in which eating whole plant foods benefits our health, while junk food and animal products undermine it?
While more studies, with more participants, clearly need to be carried out to confirm this finding and understand the mechanisms behind it, I’m perfectly comfortable with recommended a wholefood plant-based as part of a sleep improvement plan for the many clients I see who experience sleep problems. After all, what’s the downside?
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