Sleep and Diet
I love reading. So, so much. I volunteer two days a week at a local bookshop here in Cape Town. It’s such a treat to get to spend so much time looking at books, talking about books, organising, alphabetising, admiring and of course reading, books. Jodi Picoult, Santa Montefiore, Marian Keyes, Candice Bushnell, Helen Fielding, Curtis Sittenfeld, Donna Tart – they all bring me so much joy. Escaping into the world these authors dream up makes me so happy. But if you asked me to pick one book that absolutely everyone to read, it’s not actually a novel I’d be suggesting. It would be Why We Sleep by Mathew Walker. This book changed my life. It’s the type of book that gets passed on from your mother-in-law or best friend with a dramatic declaration of ‘No really, you MUST read this’. Even as someone with a relatively good understanding of the human body and lifestyle factors that impact health, I was blown away by how much I learnt about the power of sleep.
When you think of sleep you might imagine someone curled up, relatively still and motionless other than the rhythmic rise and fall of their chest. It’s a deceiving picture given just how much is happening in their brain. There is a whole host of complex essential neural activities going on in the background. I don’t feel qualified to go deeply into the different activity waves at work, the neural pathways activated or brain rhythms, but instead I want to explore the links between sleep, diet and lifestyle. I want to explain why, as a dietitian, I care so much about how much sleep my patients are getting. I’ll finish with some evidenced-based tips to improve sleep so you can come away with actionable advice.
I think it’s important to preface this with a little look at what the recommendations are and if we are meeting those. A joint consensus from the American Academy of Sleep Medicine and Sleep Research Society recommends at least 7 hours of sleep per day for adults. (1) They found that habitually getting less than 7 hours of sleep was associated with an increased risk of many chronic diseases such as diabetes, obesity, high blood pressure, heart disease and stroke (1). A YouGov poll from June of 2022 found that 35% of people surveyed in the UK got less than 7 hours, and one in eight got less than 6 hours (2). They also found that 27% of people go to bed at different times every night, more on why this is important further on.
Sleep is an essential component of health; it needs to be seen as a health behaviour and given as much importance as diet and exercise. Sleep can play an important role in so many of the body’s systems including metabolism, immune function, learning, memory consolidation and emotional regulation (3). It is important to note that research has also found negative health risks associated with too much sleep, but that is a discussion for another day. So, it’s clear that sleep is essential, but why specifically would a dietitian care so much about sleep?
Let’s think about the following hypothetical situation – John is working with a dietitian to make changes to his diet and lifestyle with the aim of increasing his fibre intake, reducing saturated fat and also increasing his daily steps. John had a bad night’s sleep on Sunday. By Monday evening, after a busy day at work, he is just too tired to prepare lunch for the next day. He decides that he can buy it at work because he knows the new ‘heart healthy soup’ would be a good option. He spends most of Monday night on the couch with a beer, watching Netflix and scrolling Instagram. At around 11 pm, he heads to bed but again has a bad night’s sleep, struggling to get sleep and waking every few hours. John wakes exhausted and this doesn’t get much better throughout the morning. It gets to lunchtime and he is already three coffees deep but hasn’t been able to concentrate properly on work. He goes to the canteen to get lunch. Unfortunately, the soup maker isn’t working so that option isn’t available. The other options are getting a hot meal or going to the salad bar and trying to make up a salad box. John is struggling to make a decision, overwhelmed by all the salad choices, so he ends up just going with the lasagne, grabs another coffee and gets back to his desk to try to make up for a slow morning.
By looking just at what John ate and how much activity he did or didn’t do, he might be considered unmotivated or ‘non-compliant’. But by taking the impact of sleep into account we can support him in a much more beneficial way. Instead of berating him for his lack of ‘willpower’, a better use of time would be exploring his current sleep hygiene to see if any changes could improve his sleep. Making changes to his diet and lifestyle would likely be significantly easier if he wasn’t fighting his hormones.
That might sound like an exaggeration of events, but my point is that poor sleep can impact so many choices we make related to diet and lifestyle, in many different ways. In order to make changes to diet and lifestyle we need to understand why we are making certain choices, and sleep is likely to be one big factor that is often overlooked. Diet, lifestyle, and sleep are intimately interlinked and can have significant effects on each other. Let’s look at what might be going on for John :
Sleep -> Diet
· Lack of sleep has been shown to be linked to an increase in the hunger hormone, ghrelin, and a decrease in the satiety hormone leptin (4,5). This will result in increased appetite and hunger.
· Lack of sleep is associated with reduced capacity for decision-making – even just one night of sleep loss was found to be associated with impairment when flexible decision-making was required (6). Making changes to diet, especially in the early days, requires this flexible thought and decision-making, especially when eating out.
Diet -> Sleep
· A systematic review of both randomised control trials and epidemiological studies
found that caffeine intake was found to reduce sleep time, sleep efficacy and perceived sleep quality (7). Interestingly a genetic link to why some individuals are more sensitive to caffeine was found (7). This may explain why some people can have a double espresso after dinner and still wake up fresh as a daisy the next morning!
· You may find that alcohol helps you fall asleep, but unfortunately, that benefit isn’t sustained through the night. You have probably heard of the sleep stages termed Rapid Eye Movement (REM) and non-Rapid Eye Movement (NREM) sleep. During a night’s sleep, you will go through approx. 4-5 cycles of these stages. Alcohol can interrupt the timing and ratios of these stages and so lower the quality of sleep and result in more sleep disruptions (8). This can also have lasting effects, as some people will experience daytime sleepiness the following day (8).
Lifestyle -> Sleep
· Stress can also affect the ratios of the sleep stages within sleep cycles by reducing REM stages, increasing awakenings and reducing sleep efficiency (9).
· Many studies have found that using screens including phones and laptops can reduce the amount of melatonin that the body produces due to the blue light emitted (10). This hormone makes you feel tired, sleepy and ready for bed at the right time. Without it, you remain alert when you should be getting ready for sleep. Blue light can also affect the timings of REM and NREM sleep stages (10).
Sleep -> Lifestyle
· Poor sleep has been found to be associated with reduced physical activity (11). Interestingly this is a bidirectional relationship and daytime exercise can help improve sleep (11).
As mentioned above short sleep has been associated with chronic diseases including obesity and type 2 diabetes. A meta-analysis of longitudinal studies found habitual short sleep time to be significantly associated with obesity (12). The proposed mechanism for short sleep and obesity is complex. Sleep deprivation can lead to reduced leptin, increased ghrelin, increased hedonic signalling when eating, increased fatigue, and increased time awake (13). These then can in turn lead to increased hunger, reduced activity and increased caloric intake and increased opportunity for eating. This relationship is bidirectional (13). Obesity itself increases the risk for sleep disorders, leading to reduced sleep duration and sleep quality, cumulating in sleep deprivation (13). As well as an increased amount of food eaten, studies have shown an increase in carbohydrates and fats consumed after short sleep (14). This is likely to be due to the changes in appetite-regulating hormones as well as increased hedonic response in the brain (14).
Another hormone whose pathway that can be negatively affected by poor sleep is insulin. Insulin is an essential hormone involved in metabolism and blood sugar control. In brief, insulin acts to regulate the movement of glucose from the bloodstream into the body cells for energy. The response by the body cells to insulin is referred to as insulin sensitivity. In type 2 diabetes this process is impaired, due to either the body no longer being able to produce enough insulin and/or the body cells are not responding to the insulin that is produced. Several lab-based studies looking at the metabolic effects of short sleep have found that short sleep reduces insulin sensitivity, leading to impaired control of blood sugar levels in healthy individuals (15). Many studies have found short sleep to be associated with developing type 2 diabetes, even after obesity was controlled for (15).
So how do I improve my sleep?
We need to look at sleep hygiene. And I’m not referring to how often you change your bedsheets. Sleep hygiene refers to the daily habits and lifestyle factors that influence your sleep. These include a range of factors including; exposure to natural light, screen use, stress management, exercise, diet, alcohol and caffeine. As with most things health-related, preparation is key! And preparing for a good night's sleep starts the moment you wake up. Exposure to natural light in the morning can help improve sleep as it regulates our circadian rhythm. This is our 24-hour body clock which regulates wake/sleep patterns. Morning light can signal to the brain that it is time to stop making melatonin, the sleep hormone (16). It also helps set an internal timer to start producing melatonin again in about 14 hours time (16).
Later in the day it may be beneficial to be mindful of your caffeine intake, most experts advise that you should have your last coffee no later than 2 - 4 pm, especially if you are sensitive to caffeine. Regular exercise and relaxation techniques/stress management during the day can also be really beneficial. These will look different for everyone so it’s worth playing around and seeing what works for you!
Getting closer to bedtime, tweaking pre-bed habits can help get those 7-9 hours:
v Set a regular bedtime and try to stick to getting up at the same time every day (from earlier, nearly a third of Brits surveyed said they didn’t do this)
v Put your phone/laptop/screen away an hour before bed and do something more relaxing instead ( read a book!)
v Reduce alcohol intake
v Optimise at your bedroom set up – aim for a cool dark quiet environment.
To wrap things up, (it’s getting late in the day and I want to get off my laptop!) sleep matters. And many of use aren’t getting enough. Many of us are making huge efforts to improve our health, but by not prioritising sleep we are doing ourselves a big disservice. Rather than tear yourself down for not sticking to your diet or exercise plan, take a look at your sleep. My last piece of advice to you is to adopt the reverse lie-in mentality – going to bed at 9:30 pm has never felt so luxurious!
P.S. I am using these great pics of Tilly because she is my biggest inspiration when it comes to prioritising sleep, she is the queen of getting a solid 22hrs of zzzz’s a day!
References
1. Watson NF, Badr MS, Belenky G, Bliwise DL, Buxton OM, Buysse D, Dinges DF, Gangwisch J, Grandner MA, Kushida C, Malhotra RK, Martin JL, Patel SR, Quan SF, Tasali E. Recommended Amount of Sleep for a Healthy Adult: A Joint Consensus Statement of the American Academy of Sleep Medicine and Sleep Research Society. Sleep. 2015 Jun 1;38(6):843-4. doi: 10.5665/sleep.4716. PMID: 26039963; PMCID: PMC4434546.
2. The YouGov Sleep Study: Part one - Sleeping patterns | YouGov
3. Perry GS, Patil SP, Presley-Cantrell LR. Raising awareness of sleep as a healthy behavior. Prev Chronic Dis. 2013 Aug 8;10:E133. doi: 10.5888/pcd10.130081. PMID: 23928458; PMCID: PMC3741412.
4. Spiegel K, Tasali E, Penev P, Van Cauter E. Brief communication: Sleep curtailment in healthy young men is associated with decreased leptin levels, elevated ghrelin levels, and increased hunger and appetite. Ann Intern Med. 2004 Dec 7;141(11):846-50. doi: 10.7326/0003-4819-141-11-200412070-00008. PMID: 15583226.
5. Taheri S, Lin L, Austin D, Young T, Mignot E. Short sleep duration is associated with reduced leptin, elevated ghrelin, and increased body mass index. PLoS Med. 2004 Dec;1(3):e62. doi: 10.1371/journal.pmed.0010062. Epub 2004 Dec 7. PMID: 15602591; PMCID: PMC535701.
6. Y. Harrison, J.A. Horne,One Night of Sleep Loss Impairs Innovative Thinking and Flexible Decision Making,Organizational Behavior and Human Decision Processes,Volume 78, Issue 2,1999,Pages 128-145,ISSN 0749-5978,https://doi.org/10.1006/obhd.1999.2827.
7. Ian Clark, Hans Peter Landolt. Coffee, caffeine, and sleep: A systematic review of epidemiological studies and randomized controlled trials. Sleep Medicine Reviews. Volume 31,2017. Pages 70-78. ISSN 1087-0792. https://doi.org/10.1016/j.smrv.2016.01.006.
8. Alcohol and Sleep | Sleep Foundation
9. Kim EJ, Dimsdale JE. The effect of psychosocial stress on sleep: a review of polysomnographic evidence. Behav Sleep Med. 2007;5(4):256-78. doi: 10.1080/15402000701557383. PMID: 17937582; PMCID: PMC4266573.
10. Can Electronics Affect Quality Sleep? | Sleep Foundation
11. Kline CE. The bidirectional relationship between exercise and sleep: Implications for exercise adherence and sleep improvement. Am J Lifestyle Med. 2014 Nov-Dec;8(6):375-379. doi: 10.1177/1559827614544437. PMID: 25729341; PMCID: PMC4341978.
12. Yili Wu, Long Zhai, Dongfeng Zhang, Sleep duration and obesity among adults: a meta-analysis of prospective studies. Sleep Medicine. Volume 15, Issue 12. 2014. Pages 1456-1462. ISSN 1389-9457. https://doi.org/10.1016/j.sleep.2014.07.018
13. Cooper CB, Neufeld EV, Dolezal BA, et al.Sleep deprivation and obesity in adults: a brief narrative reviewBMJ Open Sport & Exercise Medicine 2018;4:e000392. doi: 10.1136/bmjsem-2018-000392
14. Virginie Bayon, Damien Leger, Danielle Gomez-Merino, Marie-Françoise Vecchierini & Mounir Chennaoui (2014) Sleep debt and obesity, Annals of Medicine, 46:5, 264-272, DOI: 10.3109/07853890.2014.931103
15. Roo Killick and others, Implications of Sleep Restriction and Recovery on Metabolic Outcomes, The Journal of Clinical Endocrinology & Metabolism, Volume 97, Issue 11, 1 November 2012, Pages 3876–3890, https://doi.org/10.1210/jc.2012-1845
