• Too little sleep, too much sleep and poor sleep can all affect how much we eat. (Pexels)Source: Pexels
Find yourself reaching for fatty, sugary foods - or just really hungry - after a bad night's sleep? There's a reason for that.
Melanie McGrice

11 Mar 2019 - 9:57 AM  UPDATED 14 Mar 2019 - 9:58 AM

Not getting enough sleep? Or tossing and turning all night? It can do more than make you tired. It can make you fat, or just make it really hard to eat well.  

What many of us don’t know is that the amount of good sleep we get can affect how much we eat, and how hard it is to make healthy sleep choices. And it’s a problem that’s getting worse and worse – because most of us are getting less sleep.

Dr Linda Schachter, medical director from Sleep Services Australia, explains: “On average, if we look at historical data, we’re sleeping about an hour less than we did twenty years ago.  People are getting busier and busier, and are staying awake playing with electronic devices, and they seem to think that sleep is expendable”. 

But it’s not. Carmel Harrington, Author of The Sleep Diet, says “It is important to try to get what you need every night as sleep, along with exercise and nutrition, is fundamental for a healthy weight. Population studies show that adults need somewhere between 7-9 hours sleep every night.”

You eat more and move less

Why is sleep so important for maintaining a healthy weight?  Let’s look at some of the reasons:

  • Tiredness decreases your willpower – You know that two chocolate biscuits are enough, but when you’re tired, your willpower may also be depleted, making it harder than usual to remember the big picture and put the rest away for another time. A 2015 review of research that looked at the link between sleep and self-control suggested that good sleep habits could “refuel a person’s ability to make more difficult choices”.
  • Being tired decreases your incidental exercise – when you’re energetic it’s easy to bound up the stairs or walk to the shops, but when you’re fatigued, you may be more tempted to take the easy route.
  • Sleep deprivation can also affect your resting metabolic rate – when the body doesn’t get enough sleep it conserves energy by slowing down your body’s basic functions.  Think about how much more revitalised you feel after a holiday.
  • The more time that you spend sleeping, the less time you have to eat – do you struggle with snacking late at night? An easy way to solve this problem is to head to bed a little bit earlier.

Perhaps the most important point is that not getting enough sleep can make us hungry. Inadequate sleep increases appetite; just ask science journalist and ‘self-experimenter’ Dr Zoe Williams, who in SBS's Trust Me, I'm a Doctor (tonight 7.30pm on SBS and then watch it on SBS On Demand) undertakes her own experiment with a few buddies in a house in the Kent countryside.  Each volunteer experienced one night of undisturbed sleep, followed by a night in which their sleep was severely disrupted by a baby doll programmed to cry regularly throughout the night.  In line with the research, the volunteers found that when they slept badly, they were more likely to eat more and choose higher kilojoule foods:

A recent review found that when people are sleep deprived they consume an additional 1600 kilojoules per day!  That’s the equivalent of three slices of bread.  So, appetite control is another major reason why a good night’s sleep is essential for a healthy weight.

Sleep and hormones

You may not think that you’re doing much when you’re sleeping, but in fact, sleep has a number of important functions.  For one thing, sleeping has a big impact on our appetite hormones

  • Ghrelin – ghrelin’s job is to trigger your appetite to let you know that it’s time to eat.  However, it has been found that when people are sleep deprived, their body produces significantly more ghrelin than usual, resulting in an increased appetite.
  • Leptin – leptin is a hormone that suppresses our appetite when we’ve had enough to eat.  When you don’t have enough sleep, your body produces less leptin, resulting in greater food consumption.
  • Cortisol – cortisol levels increase when we are stressed, often causing an increase in appetite and a redistribution of our fat stores to around our waist.  Cortisol levels also increase when we haven’t had enough sleep.  Maybe this is why we also have a shorter temper when we’re tired?

A range of research has shown that sleep loss can result in increased levels of ghrelin, lower levels of leptin and increased evening concentrations of cortisol, and confirmed the link between lack of sleep and an increased risk of obesity.

So you can see that sleep is key for achieving and maintaining a healthy weight.  This doesn’t mean that you should put your feet up and sleep all day! However, if you think you burn too much of the midnight oil, then a few extra hours each night may leave you less hungry, help you make better food choices and give you the energy to participate in more physical activity.  

Watch the Insight episode on Sleep - How much do you really need, and what happens to your body when you don't get enough?  

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