Think back to a time when you felt so tired that it felt as though someone attached weights to the ends of your eyelids; when you realised that the expression bone-dead tired literally meant your bones ached. Did you feel like whipping up a healthy salad? Did you feel like going to the gym to pump out a weights session or do CrossFit? Lacking motivation in times of exhaustion is not uncommon, nor unexpected. This is one reason why sleep or lack thereof may contribute to weight gain; however there are other more physiological reasons as to why sleep deprivation impacts on your weight.
According to the Australian Sleep Health Foundation, adults need approximately 7-9 hours of sleep per night. Teenagers and school aged children require slightly more ranging from 8-11 hours. Poor sleep affects our appetite hormones, increases our blood glucose levels, and can even increase hormones known to store weight such as insulin and cortisol.
What does poor sleep mean though? Our bodies run on what’s known as a circadian rhythm (our body clock). The time of day/night that we go to sleep appears critical. It is proposed that shift workers are more susceptible to weight gain as result of altered sleep habits and disruption to our circadian rhythm. Additionally, sleep quality and duration are crucial in determining the quality of our sleep. While sleeping we transition through a number of stages. They are broadly categorised into either rapid eye movement (REM) or non-rapid eye movement (NREM) sleep. The initial stages of sleep are the NREM sleep. These are NREM1, NREM2 and NREM3 (or slow wave sleep). It is in NREM3 or slow wave sleep where restoration occurs. This is the deepest stage of sleep and it’s where our heart rate, breathing, and blood pressure decrease. Our muscles are most relaxed during this stage. Certain diet behaviours can impact the time we spend in slow wave sleep. A recent study found that a diet low in fibre and high in both saturated fat and sugar decreased the amount of time we spend in slow wave sleep. Furthermore, caffeine and nicotine have been found to decrease slow wave sleep duration.
So let’s look at a few of the side effects of poor sleep mentioned above…
Cortisol, it’s our primary stress hormone that increases our blood glucose levels, contributes to the breakdown of muscle tissue, and deposits adipose tissue (fat) around the abdomen. Poor sleep quality rather than quantity has been linked to increased cortisol levels. A number of factors may impact on sleep quality, however common influences are excessive caffeine intake (caffeine has been found to remain in the system for up to 14 hours), poor sleep habits (reading phones and devices in bed), urinary habits and stress. As you can see, looking at strategies to reduce these factors is essential for reducing excess cortisol production.
What about the appetite hormones. Ghrelin is a hormone that increases hunger, while leptin is a hormone that suppresses appetite. These two hormones are affected when both sleep duration and quality are affected. One study found that poor sleep increased ghrelin (therefore hunger), decreased leptin (in other words more hunger again), and lastly increased BMI (not surprising given the increase in hunger). I tend to think of our body in terms of evolution, if we are awake for longer than it would make sense our bodies make us hungrier to feed these extra waking hours.
Sleep has also been linked to risk factors for heart disease. A review of the evidence found poor sleep behaviour contributed to metabolic syndrome which is a cluster of risk factors such as hypertension (high blood pressure), obesity and elevated blood glucose levels.
So what can we do to improve our sleep and maintain a healthy weight? Click here to see 10 tips to achieve a good night sleep from the Australian Sleep Health Foundation. A good bed routine and sleep hygiene seems to be a great start. Evaluating your caffeine intake is also important, while being aware of the timing of your fluid intake may also prevent you from waking all night with the urge to go to the loo. Maintaining a healthy diet and maintaining a consistent exercise routine, are not only crucial for achieving a healthy weight, they are also great in order to get a good night sleep. We now live in a world with a 24 hours news cycle and subsequently our sleep duration has decreased over the last 20 years. For something that we should be spending approximately 30% of our lifetime doing, sleep is an often underestimated daily ritual; therefore prioritising your sleep is a good place to start.