Why do I feel tired after lunch? What is that post-lunch slump all about?

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We all know that feeling; big lunch, you sit down and boom, – nap time.  You fall asleep. Who hasn’t enjoyed watching a colleague lose their battle with the urge to sleep during an afternoon meeting?  The nodding head, the eyelids getting heavier and heavier…this is called the postprandial dip and is most likely to be making you feel tired after lunch. 

When we eat we produce insulin which converts sugar (in the form of carbohydrate) to energy our cells can use, glycogen.  Insulin causes an amino acid called tryptophan to be produced which, in turn, causes serotonin and melatonin to be produced.  These two neurotransmitters induce sleep, especially melatonin. Have a read of our melotonin blog here if you want to know more.

Sugar or carbohydrate heavy foods such as bread or pasta cause the most insulin to be produced and so make you the most tired.  Some high protein foods such as eggs or turkey contain high levels of tryptophan so can affect levels of serotonin and melatonin.

We have natural peak in melatonin in the afternoon linked to a drop in body temperature.  This coupled with a carbohydrate heavy lunch is likely to be the reason you feel tired early – mid afternoon. These push and pulls form part of your drive to sleep; read all about it here.

It’s worth mentioning the urge to nap in the afternoon is the result of our natural pattern of biphasic sleep (sleeping twice a day).  This appears to be natural in most populations when left to their own devices and free from the modern day pressure of a ‘full working day’.

Written by
Sam Billington

Sam is our sleep guru. I am fascinated by sleep and I've used my science training to research and learn about sleep. I have been providing sleep advice and personal sleep plans for years. My day job is Head of Workplace Culture in Defra, I live in London with my wife and have a PhD in Ecology and Biology.