Intermittent Fasting – How it Affects Sleep

It’s not uncommon for someone to try intermittent fasting, and find that they not only haveto deal with hunger, but trouble sleeping as well. I hear about this every now and then and have experienced it for myself. This especially seems to be the case if your new eating window is quite different fromyour previous habits. Actually, it makes sense that fasting initially disturbs sleep, and I’ll explain why, but interestingly, after a couple of days, intermittent fasting should have you getting better sleep. First, there are a couple reasons why fasting initially makes it harder to sleep and onecould be that when your body is deriving more energy from fat metabolism, something thathappens during Intermittent fasting, there’s increased orexin – a neuropeptide that stimulates wakefulness.

But, what’s probably more of a factor is how intermittent fasting affects your circadianrhythm – your biological clock. We’re all aware that flying across time zones leaves us feeling pretty crappy fora few days because your body’s internal clock is for example expecting it to be morningbut after you get off the plane, the sun is already going down. Once your circadian rhythm adapts to the new time zone by being exposed to light and darkat the proper times, you feel better, but then you have to deal with jet lag all overagain on the return flight. Dr.  Charles F.  Ehret, a senior scientist at the Argonne National Laboratory in Illinois, has developed a diet designed to greatly diminish the disruptive symptoms of jetlag.

The diet is a four day process involving light fasting. The first day – you get to eat, the next day you do a fast or eat very lightly of thingslike light soup or salad, then on the third day you can eat again, and on the fourth day, your day of departure – you do another light fast. Then, you continue the fasting and don’t have a proper meal until breakfast time at your destination. I’ve tried something similar to this a couple times when traveling from Tokyo to America, I don’t start four days in advance- I just eat nothing the day of my flight, nothingon the airplane and have my first bite of food at lunch time after I’ve arrived in America- This has worked surprisingly well, making it easy to fall asleep at a propertime the day I arrive and have almost no jetlag. This works because of how food affects the circadian rhythm. The body doesn’t have just one, but several different biological clocks influencing the circadian rhythm. There’s a sort of masterclock running in the brain and this is called the suprachiasmatic nucleus and it is very sensitive to blue light.

This is why it’s important not to look at screens too much before bed or at least useblue light blocking glasses or a blue light filtering app. Other than the one in the brain, there are other clocks in the body found in organs likethe liver, kidneys, pancreas and heart – these are called peripheral oscillators. Where as light most affects the clock in your brain, your food and when you eat it, is the primary controller of these peripheral clocks. So, in the way the sun coming up in the morning and the darkness at night helps your brain keep track of the time and keep a good circadian rhythm, your first bite of food and your lastbite of food tell your peripheral clocks how to set the circadian rhythm.

Considering the main premise of intermittent fasting is modifying the time frame you eatin, it’s understandable that it could mess with your circadian rhythm and your sleep. But, Intermittent Fasting’s influence on the circadian rhythm should actually haveyou sleeping better once you adapt to it. Here’s a study done by Dr. Satchin Panda and Shubhroz Gill at the Salk Institute forBiological studies. They made an easy to use smartphone app that had people log their eating habits. What they wanted to track was in how big of a time frame were people consuming anythingother than water. They found that while most people estimated that their eating window was less than 12hours, in reality it was about 3 hours longer than that. So the time from that first sip of coffee in the morning to the last bite of dessertor sip of wine at night was about 15 hours. Then, they took the people who were eating in a time frame that was longer than 14 hoursand asked them to reduce their eating window to 11 hours. Again, they didn’t have to change what they ate, they only changed when they ate.

The results were that they lost weight, felt more energetic and slept much better. As the data here show, they were far more energetic in the morning, they were more energeticoverall, they were less hungry at bedtime and were far more satisfied with their sleep. One reason for this may be that restricting your eating window improves the strength ofcircadian oscillations. Another study co-published by Dr. Satchin Panda says that “feeding/fasting rhythms enhancethe robustness or amplitude of the oscillation of circadian activator and repressor components. “Essentially, you get a more pronounced circadian rhythm in parts of the body when your foodintake is restricted to a certain time frame, like in intermittent fasting.

Here in figure 3, we see that the circadian oscillation is much more pronounced in rodentswhose food intake was time restricted. I’m not sure if it’s safe to say that this directly leads to a more pronounced sleep/wakecycle as well, but part of the reason intermittent fasting improves sleep is related to the factthat your body prefers to metabolize food at certain times. If you think about how we used to eat way back before the advent of artificial light,most of our eating would get done during the day, considering we are not nocturnal creatures. So it would make sense for hormones related to food metabolism to work against hormonesthat promote sleep. And, this happens to be the case.

This paper from 2013 explains that “an increase in melatonin levels leads to a down-regulationof insulin secretion and vice versa. ”So, the sleep promoting hormone, melatonin, can do its job easier if you have low insulin. Luckily, low insulin is one of the effects of intermittent fasting. Going back to the paper by Dr.  Satchin Panda, We see that the length of fasting paralleledthe length of sleep. A longer fasting period would lead to lower insulin levels, leading to a better secretionof melatonin and better sleep. So, Intermittent Fasting may disturb your sleep at first, but in just a couple days,it should have you feeling sleepier at night, getting better quality sleep and waking upmore refreshed in the morning.