Tired? Here's why you want that cake

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 Photo: Getty Images

When mother of four Constance Hall wrote on her Facebook page in January to 'eat the cake' as part of a letter to mothers everywhere, the advice was well received.

As she wrote, "A brand new 24 hour job that doesn't pay and won't end for around 20 years is NOT a good time to give up cake. Eat the cake, eat the whole f&*%ing cake …"

Her sentiments in that letter – which also made mums feel better for looking at their phones while their kids played in the park, and for having messy houses – certainly struck a chord, with hundreds of thousands of likes and shares.

It's easy to understand why: when you're tired, emotional, and just want a break, it's easy to turn to cake to make things feel better.

Now new research, published in the journal SLEEP, shows another reason why, when we're tired, we just want to eat all the sweet stuff.

Researchers from the University of Chicago recruited healthy volunteers to take part in a study that consisted of two four-night stays at the university.

On the first stay, the participants slept around 7.5 hours each night. The second time they stayed, they were only allowed to sleep around 4.2 hours each night.

The researchers fed the participants identical meals at 9am, 2pm and 7pm on both stays.

They then measured the volunteers endocannibinoid levels – hormones similar to those found in cannabis (marijuana) – that make eating more enjoyable.

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After sleeping normal amounts, those hormone levels were low in the morning, peaked in the early afternoon, then dropped down.

But when the participants were sleep restricted, it was a whole other story. Those levels rose 33 per cent higher, and were high from 2pm through till 9pm.

In other words, sleep deprivation pretty much gave the volunteers the 'munchies'.

And while their hormone levels were all messed up, the participants also ate differently. When exhausted, they were more likely to indulge in fatty, sugary options, like cookies and chips. They were most likely to do this when their endocannibinoid levels were highest – from 2pm-9pm.

Erin Hanlon, a Chicago University researcher in metabolism, said, "We found sleep restriction boosts a signal that may increase ... the pleasure and satisfaction gained from eating."

So when you're tired you don't just lack the willpower to say no to sweet foods – your body literally interprets them as tasting better at that time.

Of course, the takeaway message from these findings is clear: sleep is important when it comes to eating habits. You need to sleep better in order to eat better.

Yes, yes, we know that. The problem is that as parents, we don't get to control how much we sleep.

But that doesn't mean we should throw our arms up in the air and say, "Oh well, it's not our fault. Our hormones are literally against us, so we might as well eat that cake."

Instead, try to find enjoyment in other things, says clinical psychologist Dr Lara Winten from Let's Talk Psychology Practice.

She says taking a "deep mindful pause" can help reduce your stress hormone levels.

She also recommends having a cup of tea in the sunshine for a boost of vitamin D, which she explains is important for mood management.

"Taking a moment to connect with one of your key support people may increase your oxytocin and dopamine production, which are known to be the 'bonding' and 'feel good' chemicals," she says.

But sometimes, we just want that cake. There's nothing wrong with that, says Dr Winten.

"Absolutely enjoy that cake from time to time – just make sure you fully embrace the experience and defuse from any side servings of guilt."