“…all parts of the gastrointestinal tract are under pervasive control of the circadian clock, and perturbances of circadian rhythmicity through jet lag or shift work acutely manifest themselves predominantly as gastrointestinal discomfort. Long term disruption of the circadian clock in these tissues may lead to serious diseases such as colorectal cancer or metabolic syndrome.”
If you have a gut problem, the above quote may not resonate with you if you don’t work the night shift or skip over times zones while traveling. Obviously you don’t have circadian disruption, you go to bed at night just like everyone else, right?
The problem is, you don’t necessarily have to work in a fire station or take the red-eye to Europe to experience circadian disruption. In fact, Dr. Satchin Panda covers the pervasiveness of “social jet lag” in his book The Circadian Code. But just what is “social jet lag”?
What is social jet lag?
You work hard during the week and make an effort to follow a pretty strict Monday-Friday sleep schedule. Like a good boy or girl you eat breakfast, but you eat it right as you wake up at 7am. Due to your 60 minute commute, you don’t get home until 7:30pm every night at which point you have dinner.
Or let’s say you don’t have a long commute and you eat dinner at 5pm. The problem is, dinner doesn’t quite fill you up so you go back for more at 9:30pm. Just a little before bedtime snack to get you through the night. Of course you watch television right up until bedtime with all the lights on, so your eyes are bombarded with enough blue light to trick your body in to believing it’s still daytime.
Now let’s ignore the week and say you’re doing everything right Monday-Friday. In bed by 10pm, up by 7am and you’re eating schedule is great. But then the weekend rolls in and you stay up late, watching TV or partying with your friends until midnight. Your eating schedule shifts as you eat more food closer to your habitual bedtime.
In all of these scenarios, you are exposing yourself to social jet lag. Your geographical location has nothing to do with your jet lag but it doesn’t matter. What truly matters is the signals your environment is sending to your body, so whether you fly from West to East Coast or simply just shift your light exposure and feeding cycle is irrelevant.
Both situations confuse the body, whether your eating period is too long every day or you switch up your schedule twice a week. The biggest problem here is that social jet lag is something people may be imposing on themselves daily or twice a week, once when you shift later on Friday and once when you shift back on Sunday.
This is something you could be doing to yourself 52 times a year or nearly every day, which is far worse than traveling from West to East Coast a couple of times a year. And it’s no wonder how living under any of these conditions can be damaging to the gut.
Circadian rhythms in a nutshell
I’ve discussed the importance of paying attention to one’s circadian rhythms for optimizing gut health ad nauseam on this blog. Essentially, circadian rhythms are generated from our habitual behavior in an effort to optimize our chances for success in our environment. As our behavior changes, so go our circadian rhythms.
At the cellular level, circadian rhythms help segregate processes that may run counter to one another. For example, the lining of your gut completely replaces itself every 10 days or so. But it’s important not to try and replace these cells when they’re in the process of keeping things in the gut from entering the bloodstream. To determine the proper timing, they need a way to sense when it’s safe to turn over. Circadian rhythms help do that.
At the organ level, circadian rhythms help coordinate communication between systems that depend upon one another to accomplish tasks. For example, blood glucose regulation is governed by proper communication between the gut, liver, muscles, adipose tissue, liver, pancreas, brain and kidneys just to name a few. When this communication breaks down, proper blood glucose regulation goes out the window.
I use these 2 examples because our metabolism has to function properly for our circadian rhythms to promote health, especially in the gut. If your metabolism is wonky you can’t optimize your circadian rhythms. Fixing metabolic problems such as Type 2 diabetes or metabolic syndrome are first order problems. If you have either of these conditions they should be corrected first before addressing a functional gut disorder.
There’s considerable crosstalk between our metabolism and our circadian clocks. Or cells and organs can’t communicate properly with one another with an impaired metabolism, which a recent review does a terrific job of covering. You can check that our here.
Metabolism and circadian clocks
Cellular energy metabolism changes throughout the day in response to changes in circadian rhythms. While the master clock in the brain exerts some control over cellular clocks throughout the body, our behavior also plays a big role. Factors such as our feeding/fasting window, stress, and physical activity alter metabolism AND our circadian rhythms.
In order for this to work, we need signaling molecules that can allow distant tissues and organs to communicate with one another. We’re beginning to unravel many of these signaling molecules, which include at the cellular level:
- Heme iron
- NAD+/NADH ratio
- AMP/ATP ratio
- Free radicals/reactive oxygen species
- Nutrient sensing, particularly amino acids
At the organ level:
- Leptin from fat
- Ghrelin from the stomach
- Insulin and glucagon from the pancreas
- Thyroid hormone from the thyroid gland
- ACTH, TSH, & melatonin from the brain
- Bile from the liver
- Cortisol from the adrenal glands
- Irisin from muscle and fat
- Microbial metabolites such as SCFAs from the microbiome
Circadian variation in all of these signaling molecules is regulated in part by behavior, primarily a combination of physical activity and feeding. This is why being sedentary and overfeeding are detrimental to our metabolic health. We tend to focus on the physical manifestations of this combination: becoming overweight or obese.
But what if the metabolic problems that come with obesity aren’t from becoming overweight, per se? What if the behaviors that lead to obesity also lead to widespread circadian disruption and this is what causes metabolic syndrome? The data in mice indicates this may be the case.
There’s even evidence that behavior can prevent metabolic dysfunction in mice who lack functioning clocks. When mice with or without functioning clocks are fed a high fat diet with constant access to food, they become metabolically impaired. Feed them the same amount of food under time-restricted conditions and they are free of metabolic disease, whether they have a functioning clock or not. This indicates behavior is just as important as having the proper circadian machinery.
The gut is an expensive organ to maintain from an energy perspective. Impaired metabolism throws a huge monkey wrench in the gut at the cellular and organ level. So if you want to fix your gut, fix your metabolism first.