Written by: Sarah Bayliss
Reviewed by: Emily J., MSc RD
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Living out-of-sync with your circadian rhythm can have a huge impact on your metabolic health, mood, and performance. Learn the best ways to eat and sleep according to your body clock.
We’re all guilty of saying yes to more work, activities, and social occasions than our schedules allow. It’s all too easy in the modern world, where overstimulation and abundance have blurred the lines between night and day, leading us to believe we can do anything we want, when we want, no matter the time.
Unfortunately, there are real health consequences to overextending ourselves for too long. Our body is controlled by a 24-hour body clock that guides us when the best time is to sleep, eat, move, think, and repair. When we live out-of-sync with our biological clock, things just don’t work as well — we don’t feel as bright or perform at our best. Over time, this can lead to biological chaos and even illness.
The science of the body clock, also known as circadian rhythm or biological clock, is a relatively new and emerging area of research. Likely, we don’t yet fully understand the importance of our body’s clock on our health. Still, research has interesting things to say about the relationship between our circadian rhythm and lifestyle choices, including food and sleep.
Our central biological clock is an area of the brain called the hypothalamus. It guides most of our physiological functions, influencing many bodily processes, not just sleep. Our central clock receives a signal from sunlight that sets our daily 24-hour biological clock in motion and must be reset every day by our eyes being exposed to natural sunlight as we wake.
While our internal clocks would carry on even if we lived in complete darkness, light is a large part of their regulation . Studies in blind individuals have shown that many experience desynchrony of their circadian rhythms and day/night cycles, where they experience frequent insomnia and difficulty staying awake/functioning during the day .
Similar issues are seen in shift workers who sleep during the day and work at night . They frequently experience shorter, more disrupted sleep during the day, and experience poor postprandial (post-meal) glucose and insulin response to the meals that they eat during their night shift, as the body does not metabolize as efficiently during the night.
Our central clock also affects multiple processes that influence glucose metabolism, including food intake, energy expenditure, and insulin sensitivity (how efficiently cells take in glucose, allowing blood sugar to return to normal after eating).
When we’re awake, our glucose mainly comes from our food; when we’re asleep, the body utilizes glucose stores. Our biological clock adjusts metabolism based on whether we are awake or asleep. During the day, we feel hungry, we eat, and our body appropriately prepares to process our food efficiently. At night, this system rests as food is not anticipated.
We’ve evolved to eat most of our calories during the day when our bodies are more insulin sensitive. In the evenings, we are less efficient at managing glucose — i.e., we’re more insulin resistant. This increased glucose intolerance in the evening is a result of lower circadian-driven insulin release from the pancreas .
Eating too many calories too late at night disrupts our circadian rhythm — our body can’t efficiently get glucose into cells. As a result, blood sugar can remain high overnight. For many, the last meal of the day is the largest and is often eaten late due to work and family commitments.
Many of us have been told that breakfast is the most important meal of the day, and there may be some truth to this adage.
Research shows that skipping breakfast may have negative consequences on blood sugar, including high fasting blood glucose levels, higher blood glucose after meals, and impaired glucose tolerance (which means your glucose levels are high enough to significantly increase your risk of cardiovascular disease and diabetes) .
However, it’s hard to say whether skipping breakfast is primarily responsible for these symptoms since it’s also been shown that a greater percentage of those who don’t eat breakfast tend to drink more, smoke more, and exercise less — all factors which may impact glucose as well .
The bigger issue at hand is that skipping breakfast can cause you to feel hungrier than usual (and overeat) later in the day, which can wreak havoc on your glucose response and cause you to feel fatigued — triggering a cycle where your hunger hormones are disrupted and you crave even more carbs to balance your dysregulated glucose levels. If you find yourself experiencing this, avoid skipping breakfast, and try eating even a small, protein-rich morning snack if you’re not typically hungry after you wake up.
If you practice time-restricted eating (TRE), a fasting protocol where you eat your meals in a smaller eating window, you may already be skipping breakfast naturally. In the most popular form of TRE, known as the 16/8 model, individuals fast for 16 hours and eat all their calories in an 8-hour window during the day.
If you’re practicing TRE and experiencing excessive hunger later in the day or dips in energy, glucose levels, and more, try moving your eating window earlier in the day and aim to have your first meal around 10am and your last meal before 6pm. This is more aligned with our circadian rhythm, and when we’re most insulin sensitive — as our bodies wind down for the evening, we become more insulin resistant .
It's more than just the times we eat – missing out on sleep also affects our blood glucose levels and eating behavior. Sleep is critical for total body and mind wellness since it’s when your body repairs cells and resets.
Research shows that a bad night's sleep and going to bed late are linked to higher blood sugar spikes after breakfast the next day — 4 nights of poor sleep resulted in a 30% reduction in insulin sensitivity as compared to those who had 4 nights of normal sleep [7, 8].
Sleep issues may directly impact our food choices, increasing our preference for unhealthy foods . Research shows that people who have less sleep tend to eat more calories . Even partial sleep deprivation can cause a 20% increase in voluntary energy intake. Furthermore, sleep deprivation throws the hormones that regulate our hunger — leptin and ghrelin — out of whack.
A 2015 meta-analysis of prospective studies showed that individuals who sleep for short periods are at risk of developing Type 2 diabetes, and proposed an optimal sleep duration of 7-8 hours per night .
If you want to improve your sleep hygiene, stick to a consistent schedule — i.e., going to bed and waking up at roughly the same time every morning. Investing in blackout curtains or a blackout eye mask — and avoiding all screens at least one hour before bed — can help prevent light from disrupting your body’s natural melatonin production .
The time we eat and the sleep we get are both fundamental to managing metabolism and blood sugar for optimal energy, mood, and protection from chronic diseases like Type 2 diabetes.
When it comes to metabolic health and glucose, aligning your sleep and eating schedules with your circadian rhythm is key. Here are a few things to consider:
Sarah Bayliss is a registered Nutritional Therapist specializing in stress and energy management for corporate and private clients. You can learn more at her website or on Instagram.