“Have you ever thought about what the term midnight actually means? Middle of the night. And that’s what it should be for all of us but in modernity, we’ve been dislocated from our natural rhythms.” - Matthew Walker, neuroscientist, founder of the Center for Human Sleep Science, and author of Why We Sleep.
This got me thinking about sleep and its impact on the foods we consume. The first two things that come to mind when we think of body composition are usually diet and exercise - but is it possible that sleep is the third overlooked element that is hindering our weight management goals?
What is the optimal amount of sleep anyway?
According to the National Sleep Foundation, adults aged 18-64 years should be getting between 7-9 hours of sleep every night, and those of us getting less than 6 hours a night may be jeopardizing our quality of life.
Anecdotally, I have always found myself reaching for comfort foods during periods of sleep loss and stress, most notably during exam periods in undergrad and grad school. Turns out there are hundreds of studies on the topic of “sleep deprivation” and “nutrition”, highlighting very legitimate explanations for this proclivity towards junk foods, both from a physiological and hedonistic standpoint.
Underlying mechanisms
Let’s explore the reasons for why sleep deprivation may be influencing our appetite and weight.
Sleep less, eat more - Khatib and colleagues (2017) conducted a meta analysis to better understand the relationship between partial sleep deprivation and total calories consumed in a 24 hour period. Results pooled from 10 different studies showed that in a 24 hour period, groups who were sleep deprived exceeded the control groups caloric intake by an average of 385 kcals. Now you might be thinking: Okay, but wouldn’t the sleep deprived group also burn more calories precisely because they're awake longer? Interestingly, only 6 out of 10 studies analyzed participant's energy expenditure - 2 studies found a significant 5% increase, while the remaining 4 studies found no significant difference in activity level within the sleep deprived group. Although studies in this meta-analysis were short term, the longest being 2 weeks, the results are quite striking and appear to suggest a causal relationship between sleep deprivation and increased caloric intake.
TYPES of calories - So the research here is mixed. Some studies showed that sleep loss led to increased cravings for carbohydrate rich foods. Other studies found participants consumed significantly more saturated fats with a decrease in their protein intake compared to control. Bottom line: none of the studies demonstrated a proclivity amongst sleep deprived individuals to seek more desirable sustenance like, fruits, vegetables, or protein rich foods.
Insulin resistance - Insulin is the hormone that shuttles the sugars we consume from our blood, into the muscle and other organs of the body. Insulin resistance is the hallmark of type 2 diabetes and there is evidence to show that sleep loss may lead to this very condition - forcing the pancreas to work harder by releasing extra insulin, in order to allow our blood sugars to normalize. Interestingly, this finding was consistent across studies that had participants (healthy men and women aged 19-23) undergoing an acute 24-hour sleep deprivation period, but also in a study looking at chronic and more mild sleep loss (4 hours per night instead of 8.5 hours that the control group received.)
Sleep deprivation = form of stress - Typically during acute stress, i.e finding out a loved one is in the hospital, our appetite becomes suppressed. However chronic stress i.e sleeping 5 hours during weeknights, typically leads us to crave, seek out, and consume more palatable fatty foods. One theory for this has to do with increased levels of cortisol during sleep loss. Cortisol is the stress hormone that controls our blood sugars and blood pressure. From an evolutionary standpoint, cortisol was released as part of a fight-or-flight response, helping our ancestors deal with the fear and stress of coming face to face with a predator. It stimulates our bodies to break down muscle protein, cascading a physiological chain reaction such as elevated blood sugars and blood pressure, suppression of our digestive system and other body functions that aren’t crucial to our survival. Back then, this better equipped our ancestors with running away from a threatening situation. Today however, the combination of sedentary lifestyle and chronic elevation of cortisol that comes with sleep deprivation may be leading to unnecessary muscle loss and as a result, slowing our metabolism.
In addition to regulating cortisol and insulin, studies show that insufficient sleep dysregulates leptin and ghrelin - the hormones that directly influence our hunger. These hormones communicate with our central nervous system, specifically the hypothalamus region of the brain, which is the appetite center of our body. Ghrelin is secreted from the stomach, triggering hunger and appetite. One study found that a total night of sleep deprivation lead to a 22% spike in ghrelin levels , heightening hunger cues in a group of healthy men. Leptin is the hormone that opposes ghrelin. It's secreted by our fat cells to signal satiety at the end of mealtime. One study looked at differences in leptin levels after participants slept for 4, 8, or 12 hours, for 6 consecutive nights. The group that slept for 4 hours experienced a 20% drop in blood leptin levels compared to the group that slept for 12 hours, suggesting the sleep deprived group may experience an increase in their appetite. To put this all into simple terms: when we experience sleep loss, our bodies take that as a sign of low energy. This may lead to increased hunger as a result of increased ghrelin, and potential overeating as a result of decreased leptin.
Although the implications of these findings affect all of us, those experiencing inconsistent sleep patterns such as doctors, nurses, and night-shift workers, may especially be prone to the side effects of sleep deprivation. These individuals may benefit greatly from meal planning and sleep patterns exceeding 7 hours for each 24 hour cycle.
Understanding these influences, relationships and their physiology can help solidify a more proactive approach with respect to nutrition, sleep patterns, and overall health.
Summary and tips
Take away message from all of these studies? Sleep is by far not the only factor when it comes to weight management, but it is important to place sleep higher on our list of priorities, to the best of our ability. Perhaps doing so will be the catalyst for all the other pieces of the puzzle, allowing us to eat better, train harder, and perform our jobs with more ease and efficiency. I will leave you with some tips for a better sleep:
1. Cool off: the body needs to cool down in order to prompt sleep, so keep the room at 21 degrees Celsius or lower.
2. Turn off all lights: whether it's your cell phone, TV, laptop, or the lights in your room. Try and create a dark environment 30 min-1 hour before bed since light inhibits serotonin production and radiation from cell phones may inhibit melatonin.
3. Avoid alcohol and caffeine in the late afternoon: although you may think alcohol is a sedative that is helping you sleep better, sedation and restful sleep are not the same thing. Alcohol may actually be inhibiting progression into REM sleep.
4. Exercise: get at least 30 min of exercise per day but avoid overexerting yourself in the late evening, right before you are going to bed.
5. Be consistent: sticking to a regular bedtime will help normalize your hormones, including melatonin.
6. Relax: find something that relaxes you whether it's meditation, listening to calm music, or petting your cat.
7. Satiety: Both hunger and feeling overly full can impair sleep - have a light snack instead.
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