How eating late may impair sleep and insulin response
Disclaimer: I am not a doctor, nor do I intend to play one on the internet. This post is for informational purposes only.
I remember sitting with my roommate, in the evening, watching an episode of Doctor Who. The mixture of time-travel, random creatures popping up and the stochastic nature of the plot makes Dr. Who a good way for me to shut my brain off at night.
It was past 10 pm, and I was having a snack at the same time. After all, I had trained that day so it’s alright. Plus, I was not eating anything that would be generally considered as “unhealthy” though. Just a mix of blueberries, nuts, avocadoes, honey<insert any food that sounds hipster here>.
This, however, is a habit that I started slowly eliminating. Although I still do that from time to time, in this post I am going to explain why eating late at night is possibly not the best strategy.
Before I begin, I still want to remind you that I still do eat late sometimes. And when I do, well… I just try to enjoy it :)
Let’s begin.
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“When you eat” is as important as “what you eat”
I’d guess most people would not doubt that what you eat is important. Although there are different diets that dictate different things, most will have different points in common such as avoiding hydrogenated oils or processed foods.
We know that what you eat does impact how your blood glucose level fluctuates. But the timing of meals is also highly important. Good examples of the importance of timing are: Time restricted eating (eating all meals within a small time window) and Intermittent fasting (cycling between eating periods and fasting periods). Both are shown to trigger some beneficial effects on inflammation and metabolism even if the meals consumed are the same.
However, I am going to argue that having a meal late at night, as opposed to having the exact same meal earlier in the evening, will have a different effect on blood glucose levels. In other words, the fluctuations in plasma blood glucose levels will vary for the same meal depending on when it was taken during the day.
Due to circadian rhythmicity, our metabolism changes throughout the day.
According to studies performed in [1] published in the journal of endocrinology:
When healthy adults eat identical meals for breakfast lunch and dinner, postprandial glucose levels are the lowest in the morning after breakfast and highest in the evening after dinner.
Figure 1- Glucose responses in response to the same meal (43% carbohydrates) given at 08:00, 14:00 and 20:00. The area under the curve is more than 2-fold larger in the evening than it is in the morning. [1]
As you can see in Figure 1, the area under the curve is twice as large when the same meal is eaten around 20:00 as opposed to eaten in the morning.
Figure 2 — Extract of [1]
While this can be due to many different factors, one interesting finding [2] is that variants in the gene encoding melatonin receptor 1B (MTNR1B) were consistently associated with fasting glucose across multiple studies. This is most likely due to how melatonin affects insulin production in the pancreas.
Enter melatonin
So, what is melatonin anyway?
Melatonin is best known as a regulator of seasonal and circadian rhythms melatonin regulates over 500 genes.
Melatonin starts kicking off about 2 to 3 hours before sleep.
Of course, this depends on different factors from genetic factors to environmental factors. So it can change if our circadian conditions are not optimal such as being jet-lagged or being exposed to a strong source blue light at night (such as laptop or phone screens).
In a recent study [4], Melatonin has been shown to bind to receptors on the pancreas. This signals to the pancreas to stop producing insulin.
Figure 3 — extract of [4]
Insulin is a hormone that enables glucose to be taken into our cells.
That means that the plasma blood glucose levels would remain elevated because the glucose is not used by the cells.
The possible impacts of late-night eating
Regular late night eating causes higher fasting plasma glucose.
And the summary of its impact is this:
With high plasma blood glucose comes high responsibility
Ok, that is a terrible way to put it and I apologize for that. So, here’s what it really means:
It is clear that this is of higher concern to people with Pre-diabetes and type-2 diabetes. However, the following points show that it matters a little bit more.
High fasting plasma glucose can have detrimental effects on brain health. For example one study showed that individuals with high plasma glucose levels may experience more brain atrophy with age. Specifically, a greater loss in brain volume in the hippocampus and the amygdala (regions of the brain that are involved in learning memory and cognition).
Figure 4 — Source [8] image by foundMyFitness
Impaired Sleep: high glucose levels can lead to different types of sleep disturbances. According to [7], the three respiratory indexes and the number of nocturnal awakenings are highly correlated with the coefficient of variation of the fasting blood glucose recorded over the 7-day period.
Figure 5 — A simplified schematic representation of the pathways linking sleep disturbances and circadian misalignment to altered glucose homeostasis and type 2 diabetes (refer to text for details). EE energy expenditure, GH growth hormone, OSAobstructive sleep apnea, REM rapid eye movement, SWS slow-wave sleep, TSHthyroid stimulating hormone, T2DM type 2 diabetes mellitus [3]
This impaired sleep also puts the individual at a higher risk for Type 2-diabetes. Disturbed sleep causes the beta cells in your pancreas to stop being sensitive to the signal of high glucose. You can listen to this short conversation [6] between Rhondha Patrick Ph. D. and Matthew Walker Ph. D. where they discuss this issue. This creates a cycle that we’re better off not getting into: Poor sleep, higher glucose; Higher glucose, poor sleep.
“It’s all part of the energy intake expenditure system. And sleep, you know, if you think about like a weighing scale between sort of energy expenditure and energy consumption, sleep, if you’re not getting it, just annihilates that balance.” —Matthew Walker Ph.D. Source: [5]
Conclusion
Even with this in mind, I will still enjoy the occasional snack here and there without worrying about it. Just like I would enjoy some good ice-cream every now and then, or some freshly made crêpes on a brunch with friends… ¯\_(ツ)_/¯
It is true that eating at night is only part of a big equation. It is also true that other things like eating more mindfully, avoiding refined carbohydrates and processed food or other food-related choices are most likely to have a higher impact on our overall wellbeing. But the point is (at least in my opinion) to focus on building better habits.
Although choosing when to eat has been more of a luxury for me rather than a virtue, I still believe that choosing to value the long term over the short term gratification should be the rule and not the exception.
Hugs, love, and all the good stuff.
Thanks for reading! :) If this added value to you, give it some claps. It would mean a lot to me and it helps other people see the story.
References
[1] Eve Van Cauter, Kenneth S. Polonsky, André J. Scheen, “Roles of Circadian Rhythmicity and Sleep in Human Glucose Regulation”, Endocrine Reviews, Volume 18, Issue 5, 1 October 1997, Pages 716–738, https://doi.org/10.1210/edrv.18.5.0317
[2] Prokopenko, Inga et al. “Variants in MTNR1B influence fasting glucose levels.” Nature genetics vol. 41,1 (2008): 77–81. doi:10.1038/ng.290
[3] Adhikary, N., Shrestha, S.L. & Sun, J.Z. Diabetol Int (2017) 8: 14. “Metabolic disturbances: role of the circadian timing system and sleep.” https://doi.org/10.1007/s13340-016-0279-6
[4] Mulder, H., Nagorny, C.L.F., Lyssenko, V. et al. Diabetologia (2009) 52: 1240. “Melatonin receptors in pancreatic islets: good morning to a novel type 2 diabetes gene” https://doi.org/10.1007/s00125-009-1359-y
[5] Full podcast episode on FoundMyFitness, a conversation between Rhondha Patrick Ph. D. and Matthew Walker Ph. D. https://www.foundmyfitness.com/episodes/matthew-walker
[6] short video conversation between Rhondha Patrick Ph. D. and Matthew Walker Ph. D. on the impact of sleep on blood glucose https://www.youtube.com/watch?v=fjG-2jIFnAY
[7] Tatti, Patrizio et al. “Sleep apnea, sleep disturbance, and fasting glucose variability: a pilot study.” Journal of diabetes science and technology vol. 7,3 743–8. 1 May. 2013, doi:10.1177/193229681300700320
[8] Nicolas Cherbuin, Perminder Sachdev, Kaarin J. Anstey “Higher normal fasting plasma glucose is associated with hippocampal atrophy” Neurology Sep 2012, 79 (10) 1019–1026; DOI: 10.1212/WNL.0b013e31826846de