The closest most of us get to food while we are sleeping is to dream about it, so how important can the relationship between our diet and sleep possibly be? It’s a surprisingly intimate and complex one that researchers are still trying to understand. But a new study sheds some light.
How Sleep affects our diet
Experts know that eating when we are meant to be sleeping, for instance, increases the risk of weight gain and cardiometabolic disorders. This is because our eating patterns are out of whack with our body clock and the timing of the hormones that regulate our appetite and metabolism. It can also lead to an energy expenditure imbalance where people burn fewer calories.
So, even if the foods you’re consuming don’t change, eating at night will have a different effect to eating during the day.
“There is increasing evidence that eating late into the night and/or the early hours of the morning may put extra strain through processing food at times when our circadian system (governing our 24-hour body rhythms) is priming us for sleep,” says Jill Dorrian, an expert in chronobiology and professor of psychology at the University of Adelaide.
Not getting enough sleep can interfere with our hormones and metabolism in similar ways. And people who haven’t had enough sleep don’t just tend to eat more (because hunger hormones weren’t properly regulated during sleep), they’re also more likely to make poor food choices. In that cohort, an extra 30 minutes to 1.5 hours of shut-eye a night, some research suggests, can reduce appetite and food cravings.
But the sleep to food relationship is not unrequited. What we eat also affects our sleep.
How diet affects sleep
Some research has suggested that eating an unhealthy diet high in sugar and saturated fat can affect sleep. The question is: how?
A study, published in the journal Obesity earlier this year, sought to answer that question.
For the study, 15 healthy men were randomly assigned either a high-sugar, high-fat diet (high fat yoghurt and granola; pasta with meatballs and sweet tomato sauce; pizza with a chocolate bar) or a low-fat, low-sugar diet (low-fat yoghurt and unsweetened muesli; pasta with peas; salmon and vegetables). All participants were told to eat at the same times each day and the diets were calorie matched.
Though there was no impact on how long the participants slept, polysomnography recordings showed those on the unhealthy diet had less deep sleep and a lower amplitude of delta brain waves.
Deep sleep and delta waves affect memory consolidation, mood, attention and glucose metabolism.
Their findings provide insight into how consumption of an unhealthier diet might change our sleep patterns in a way that results in a “less restorative or less youthful state”, the authors found. The effects reflected those of ageing and insomnia.
Though more research is needed, it is “critical evidence” of the impact diet has on our sleep, says Dr Jade Murray of Monash University’s Turner Institute for Brain and Mental Health.
Macros and micros that matter
“The study’s findings suggest that it’s the specific combination of high fat and high sugar that might impact sleep quality,” says Dr Grace Vincent, a senior lecturer in psychology at the Appleton Institute.
Although researchers focused on the fat-carbohydrate composition, the overall quality of the diet is what matters, Vincent adds. Different macronutrient breakdowns – a diet can be high in healthy fats or high in healthy carbohydrates or high in fibre intake – can all enhance deep sleep.
Certain micronutrients might also have a potent effect on our sleep.
“Foods with tryptophan, melatonin, and phytonutrients (like cherries) are associated with improved sleep,” Vincent says. “These positive effects might be due to how these foods influence the body’s production or use of serotonin and melatonin, two chemicals essential for sleep regulation.”
Foods high in tryptophan include turkey, chicken, tuna, milk, yoghurt, eggs, bananas, chocolate, nuts, seeds and legumes.
Cherries, which contain melatonin, might also improve sleep while a compound found in marine plants, like sushi seaweed, have shown potential in promoting sleep by binding to specific sites in our brain that are associated with sleep regulation, Vincent adds.
While they are all good foods to eat, no single food is a silver bullet and some research suggests that, for them to have an effect, we would have to consume unrealistically high quantities.
When you eat really matters
Two dietary changes that certainly can help our sleep quality are ensuring we don’t have caffeine within about seven hours of bed or more than a couple of alcohol-containing drinks within three hours of bed.
Considering when we consume food or drink doesn’t just apply to psychoactive substances like caffeine and alcohol.
“It is not only what we eat, but when we eat, that is important for health outcomes,” says Dorrian. “Shifting calories to earlier in the day – having a heavier meal earlier – is likely to be beneficial for metabolism.”
Along with having heavier meals earlier in the day, we should consider having our final meal around dusk when possible, says Murray.
“Light is the greatest synchroniser of our body clock, but meal timing can adjust the timing of our body clock as well,” she explains. “We shouldn’t be exposing ourselves to bright light after the sun goes down … our food should follow a similar pattern. Yet, we artificially extend all of these things.”
Increasingly, she says, the research illuminates just how important the connection between our diet and our sleep is.
“There is a very complex relationship between meals, food timing, macronutrients and our sleep,” Murray says. “A balanced diet is just as critical for our sleep as it is for maintaining good physical and mental health. And sleep has such a big role in our overall health.”