Circadian rhythms, stress, and building resilience

Stress is something most people try to avoid. But the truth of the matter is, it’s also something that makes us stronger. For example, the beneficial effects of exercise happen because it stresses the body.

But this doesn’t mean that stress is always good. Stress can build us up, but it can also break us down. Whether a stressor is good or bad depends on our ability to recover from it. It also depends on when we apply it, which system it affects, and our current stress load.

With regard to gut health, I think a lot of people misapply the principles of stress. Rather than building resilience, they pull things out of their diet that they perceive as toxins or stressors. I covered how this can backfire in a blog you can find here.

As an acute approach this is warranted. If your gut isn’t resilient, adding stressors only causes more damage. But doing this long term has devastating effects on the gut. Over the long haul, it effectively decreases resilience.

In this blog I’ll cover the basic concepts of stress and how applying it properly builds resilience.

Understanding homeostasis

When most people hear the word stress, they often think of bad things. A demanding boss with unrealistic expectations or a difficult family member for example. Things that cause anxiety.

But stress isn’t necessarily bad. In fact, stress is simply your response to an environmental threat that challenges homeostasis. Homeostasis is the tendency of the body to maintain stability of biological processes.

For example, eating increases blood glucose which causes the release of insulin. Insulin causes cells throughout the body to take in glucose, bringing glucose back down in to the healthy range.

Alternatively, when we a haven’t eaten in a while or we exercise, blood glucose would normally drop. But the pancreas senses low blood glucose and secretes glucagon. Glucagon signals the liver to release glucose to maintain blood glucose within this same range.

Homeostasis is that narrow range in where blood glucose is maintained. It’s maintained within that range because there are repercussions for being too low or high. However, as you can tell from the above, you can get to that range in many different ways. Eating and fasting are 2 ways to stress the system, and as long as everything is in working order, you maintain homeostasis.

Allostasis: How you get there is as important as getting there

Let’s say we have 2 different people, both within the healthy range of fasting blood glucose. Despite both being at 95mg/dL, one is pumping out twice as much insulin to maintain that level. In other words, the pancreas in that individual is working twice as hard.

Even though both are at homeostasis, one requires much more work from their pancreas. Over time this is a problem. The person pumping out twice as much insulin to maintain homeostasis is putting an increased load on their pancreas.

Allostasis is the process by which we achieve homeostasis. Allostatic load refers to the wear and tear we experience while maintaining homeostasis. It’s essentially the cost of maintaining homeostasis.

In this example, the allostatic load on the pancreas of the individual with higher insulin levels is higher. Over time this can lead to Type 2 diabetes as the pancreas is overworked, even though they’re currently “normal”.

Cortisol and allostatic load

I used blood glucose as an example of homeostasis and allostasis because it’s simple. Obviously our entire physiology is much more complex. But the basic principles still apply.

When we apply stress to a system or systems within the body, this increases the allostatic load. And since our health depends on the integration of all our systems, increasing allostatic load in one system typically increases it over all systems.

One of the most important systems for maintaining homeostasis and managing allostatic load is the HPA axis. When exposed to a stressor that challenges homeostasis, the HPA axis secretes cortisol. When the stressor disappears, cortisol comes back down.

Allostatic load depends on:

  • The number of stressors
  • Intensity of each stressor
  • Length of stress exposure
  • Recovery between exposures

We need stress to build resilience, but we also need something else. Synchronized circadian rhythms.

Circadian rhythms and allostatic load

In addition to stress, the circadian timekeeping system also regulates cortisol secretion. This makes sense, circadian rhythms help prepare our body for predictable environmental changes. It’s essentially an internal clock that tells us and our trillions of cells how to promote survival.

But the circadian system also regulates our sensitivity to cortisol. Exposure to stressors can alter this timing system, as can behaving in a way that is “confusing” with respect to time. Exposure to light at the wrong times or eating at the wrong times are 2 great examples.

Circadian disruption increases allostatic load. Both through directly increasing stress and impairing recovery.

Circadian rhythms and stress

Circadian rhythms help our body build resilience in many ways. First, circadian rhythms regulate our sensitivity to the stress response. For example, we are more sensitive to stress in the evening, when our cortisol level should decline.

Secondly, circadian rhythms help build resilience by separating processes that oppose one another. A great example of this at the cellular level involves the metabolic cofactors NAD+/NADH.

Circadian rhythms at the cellular level

We use NAD+ as a cofactor for breaking down our food in to usable energy, called ATP. Thus, in order to create enough energy for our active phase, we need sufficient NAD+, which gets converted to NADH and then gets recycled.

Conversely, we use NAD+ as a cofactor for the DNA repair enzyme Poly (ADP-ribose) polymerase (PARP). NAD+ is also consumed when there is inflammation via the enzyme CD38. In order to generate enough energy, we want to separate these processes from energy metabolism.

Circadian rhythms at the organ level

Circadian rhythms are also at play at the organ level. Being diurnal creatures, we sleep at night and have a prolonged period without food. Too much insulin at this time would cause our blood glucose to tank, causing hypoglycemia.

Fortunately, we secrete the hormone melatonin to help us fall asleep. Melatonin also inhibits insulin secretion, so it helps stabilize blood glucose during our fasting period.

These examples help illustrate why circadian rhythms are important for building resilience. These things don’t happen at specific times just because. They happen at specific times because the circadian system puts them all on the same time.

When our behavior is out of line with our circadian biology, that’s a stressor on the body. Making things worse, it negatively impacts our recovery from other stressors as well. As a result, resilience goes out the window.

You can apply these same principles to every organ system in the body.

Circadian rhythms, stress, and resilience

Hormetic stress: Building resilience

Regular exposure to the right amount and types of stress with adequate recovery builds resilience. We challenge our systems, recover, and come back stronger than before. And if our circadian rhythms are in line with our biology, that’s a homerun.

This concept of just enough stress to alter homeostasis and increase allostatic load is called hormesis. If we do this in a pragmatic way and pay attention to allostatic load, that’s a one-way ticket to resilience.

But approaching stress as something to avoid decreases resilience. A great example of this is what happens in a ketogenic diet. Carbohydrates generally have the greatest effect on increasing blood glucose. And in a ketogenic diet you bring carbohydrates to a minimum.

As a result, the longer you stay on a ketogenic diet, the less resilient you become to a carbohydrate load. This is primarily because you aren’t applying allostatic load to the pancreas. The first 50-75g of carbohydrate you consume at one sitting will cause hyperglycemia.

But if you slowly introduce carbohdyrates the pancreas slowly but surely becomes more able to hand the allostatic load and your resilience to carbohydrate increases.

We can apply this concept to every individual organ system in the body. Ultimately the allostatic load on your entire body depends on the allostatic load in each system. All systems communicate with one another and stress in one system affects them all.

Applying allostatic load to the gut

This concept of allostatic load is why I’m not a fan of long term restriction diets. Certainly they’re useful if the gut is under too much allostatic load and you want it to recover. But long term, it decreases resilience in the gut in the same way that carbohydrate restriction does in the pancreas.

By removing all exposure to stress, the gut loses resilience. Furthermore, other bad habits that have no direct relationship to the gut decrease resilience there as well. Resilience in one system builds resilience in others.

When people think of the gut-brain, gut bone, or gut-liver axis, they only think of it in one direction. They feel that improving gut health improves these systems. But the truth of the matter is these systems also regulate the gut. Below is a list of the axes between the gut and other organs with evidence these organs affect the gut:

I think most people approach gut health with the idea that improving gut health will fix problems with other organs and tissues in the body. But given these are bidirectional relationships, it may a better idea to address all of these systems at once.

Conclusion

Building up our resilience requires us to expose ourselves to stress from time to time. Allostatic load is the cost of maintaining homeostasis, and is central to building up resilience in our tissues and us as a whole.

Activation of the HPA-axis is the classical way we deal with stress as a whole. Since circadian rhythms regulate the HPA-axis also, we have to take them in to consideration.

A recent review article covers this succinctly, although it’s a rather dry read. The basic takehome is that to build resilience, regular exposure to hormetic stress coupled with optimized circadian rhythms are a must.

But the same concepts that apply to to our entire body also applies to each individual system. And since these systems are intricately linked, building health requires us to address them all.

When people think of the resilience in the gut, they ignore the bidirectional relationships between the gut and other organs. You cannot have a healthy gut with behaviors that decrease resilience elsewhere in the body. You just can’t.

Advertisements

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.