Feeling sleepy after a big meal? Is moving to the couch the only activity you’re capable of after Christmas lunch? You may just have been the victim of a food coma. Food comas are a real thing. And there is plenty of science to explain why the food binge you just took part in has done what it has to you. In this podcast, I explore the food coma in all its physiological and neurological glory and explain how you can help prevent it.
At some point or another, everyone has experienced the classic symptoms of a food coma. You know what I’m talking about here. It’s that overwhelming feeling of fullness after a buffet binge or that long multi-course restaurant meal including the filling of your dessert stomach.
Food comas really are a thing. The scientific name for a food coma is postprandial somnolence, but food coma is catchier. So catchy in fact that in 2014, the Oxford dictionary added ‘food coma’ as a word.
A food coma is usually described as a feeling of extreme fatigue or lethargy that can last for several hours. While the cause of after-meal sluggishness is up for debate, there is no confusion about the symptoms: laziness and heaviness, usually accompanied by bloating and a feeling of tightness in the belly.
So, what is it about eating a big meal that makes us so sleepy? Quite a few things are going on behind the scenes to do with our physiology, so let’s dive in and explore them.
To start with, when we are busily digesting our meal, more blood is shunted to the stomach and intestines to help transport away nutrients from food. With less blood in other parts of the body such as the brain and muscles, this can cause some people to feel a little light-headed or tired.
The digestion process also causes a shift in the activation of our autonomic nervous system. We move away from the ‘fight or flight’ activation tone of our nervous system and more towards the ‘rest and digest’ scheme. The larger the meal, the greater the shift.
Then there are a whole bunch of hormones involved in the digestion of food. One, in particular, is called cholecystokinin or CCK for short. CCK is linked to making us drowsy, probably by influencing the production of the neurotransmitters serotonin and melatonin. Serotonin makes us feel good. It also makes us relaxed and sleepy as well. While melatonin is a key player in regulating our sleep and wake cycles.
High glycaemic index carbohydrates could also be playing their part in the food coma cascade. Having a lot of glucose available from quickly absorbed carbohydrates can mean a spike in the production of insulin. Insulin helps your body absorb glucose from the bloodstream after a meal. With more insulin in the blood, the brain can take up more of the amino acid tryptophan. Tryptophan is the precursor for the brain neurotransmitter serotonin so it is ‘hello’ to rest and relax time.
Intuitively it would seem that eating foods high in tryptophan such as milk or turkey before bed would help increase serotonin production, but the opposite is true. The reason why is because carbohydrates are needed to stimulate insulin secretion which results in that insulin shunting small amounts of tryptophan into the brain. Consuming a high-protein meal, on the other hand, will cause a lot of amino acids to enter the brain and will probably have a stimulant effect rather than a soporific.
A common myth says that turkey is very high in tryptophan which causes sleepiness, but the context of this myth is key – it comes from the North American tradition of Thanksgiving where turkey is the key food along with a LOT of eating and napping afterwards – your classic food coma. However, the amount of tryptophan in turkey is on par with that in chicken and beef.
Back to the topic of high glycaemic foods and sleepiness, there is some research to support this which could actually be a positive for those suffering from insomnia. Eating high GI carbohydrates will stimulate insulin production and insulin has a potent ability to promote glucose and amino acid uptake into the body's cells, but it does a poor job of promoting tryptophan uptake resulting in a higher blood concentration of tryptophan in the blood and leaving more of it available to enter the brain. This process is thought to explain at least in part why someone can feel sleepy and relaxed after a meal high in carbohydrate, but awake alert a high-protein meal.
Researchers from the University of Sydney have studied whether high GI foods, which cause higher peaks in insulin secretion, can help in bringing forward the onset of sleep. The theory was that the insulin spike from eating high GI foods would increase tryptophan uptake into the brain and result in a more relaxed and sleepy person. And I’ll link to this study in the show notes. https://pubmed.ncbi.nlm.nih.gov/17284739
Twelve healthy men were given either a high GI meal (in this case it was Jasmine rice) or a low GI meal (Mahatma long-grain rice was used here) either 4 hours or 1 hour before their regular bedtime. The test was repeated on three random nights over a week. The time to sleep onset in men fed the high-GI meal 4 hours before bedtime was 9 minutes which was half that of men fed the low-GI meal who took 18 minutes to fall asleep. When meals were given 1 hour before bedtime, similar differences in sleep onset was seen – in this case, 9 minutes versus 15 minutes for the high GI and low GI meals respectively.
The results of the study are interesting though the small number of people in the study does mean that follow-up studies are certainly needed. The researchers did not measure blood tryptophan or serotonin levels in the volunteers so it is not possible to know if the effects of GI on sleep onset, if real, are related to these factors. The study was performed in healthy males, so it is unclear how the findings relate to other groups of people such as people with chronic sleep disturbances.
And the final factor that is linked to food comas is our circadian rhythm. A circadian rhythm is a natural, internal process that runs on a 24-hour cycle and is part of the body’s internal clock, running in the background to carry out essential functions and processes. One of the most important and well-known circadian rhythms is the sleep-wake cycle. Different systems of the body follow circadian rhythms that are synchroniSed with a master clock in the brain. This master clock is directly influenced by environmental cues, especially light, which is why circadian rhythms are tied to the cycle of day and night.
Thanks to our circadian rhythms, we naturally feel a dip in our energy levels around 1 or 1:30 pm, but that can vary depending on when you wake up. Whether you eat lunch or not doesn’t matter, you'd still get sleepy around this time. But a larger lunch would accentuate the sleepiness thanks to the factors I’ve already outlined.
So, if you want to minimise food comas because you may just have to get on with life and attend to some important things, here are my tips.
Don’t overeat. The bigger the meal, the bigger the food coma.Don’t go too carb crazy. Plenty of protein may help blunt the food coma effectAvoid heading straight to the couch after a meal. A small amount of activity will help use the excess glucose in your bloodstreamConsider having an earlier lunch just before midday to avoid amplifying the early afternoon dip which is part of our natural circadian rhythmChoose carbohydrate foods that have a lower glycaemic index such as wholegrain bread and pasta, legumes, most fruits and sweet potatoTake it easy on the booze. Alcohol is a sedative so will only lull you off quicker.
Or you could just embrace the food comas as part of food festivities and just before you snooze off on the couch, you can think about all that amazing physiology that is happening inside of you.
So that’s it for today’s show. You can find the show notes either in the app you’re listening to this podcast on if it supports it, or else head over to my webpage www.thinkingnutrition.com.au and click on the podcast section to find this episode to read the show notes.
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I’m Tim Crowe and you’ve been listening to Thinking Nutrition.