Updated: Oct 21, 2019
The Autonomic Nervous System Imbalance
The second aspect of an animal-based diet is a most interesting one, it also happens to be my favorite. This is the concept of an imbalance in the stress response aspect of our Autonomic Nervous System. This is a major driver in not only heart attacks but in many chronic ailments (1,2,3).
Before we get into that let’s review. In Part 1, we laid out the events that lead up to and cause a heart attack. In Part 2, we discussed how dietary fat does not cause heart disease and how it is protective against heart attacks. If you missed either of those go back and read them first before you press forward. Here is the timeline of the series.
Part 1 – The Foundational Imbalances That Cause Heart Attacks
Part 2 – Cholesterol, Fat Burning, Ketones, and Metabolic Flexibility
Part 3 – (This post) The Autonomic Nervous System Imbalance
Part 4 – Toxins, Oxidative Stress, and Nitric Oxide
Part 5 – The Evolutionary Mismatch Behind It All
Let’s dive into this second concept. Humans, as well as all mammals, have what is called an Autonomic Nervous System (ANS). It is the aspect of our nervous system that is monitoring our external environment to determine if we are in a safe or threatening situation. Depending on which it is, it will tell your body to have the appropriate reaction.
There are two aspects to the mammalian ANS, the sympathetic and parasympathetic, and dominant stimulation of one or the other tells your body which response to stress to have. The sympathetic is the “fight or flight” aspect that is used to helps us fight off or flee from a threatening situation while the parasympathetic is the “rest and digest” aspect that takes over when everything is “safe” and we can focus on digestion and metabolism.
The information for the ANS is communicated in the nervous system through one of the cranial nerves called the vagus nerve. The part of the vagus nerve associated with the sympathetic signal is called the dorsal motor nucleus (DMN) and the part associated with the parasympathetic aspect is called the nucleus ambiguous (NA) (4). But this dual vagus nerve system wasn’t always this way.
Most reptiles, and anything that evolved before reptiles, had a single vagus nerve tract. The dorsal motor nucleus was the only aspect of the vagus nerve in these animals. Because the animals were very metabolically slow (think cold blooded like reptiles) this was all they needed. If they had an extreme stress response that over stimulated the vagus nerve it would cause their body to severely slow down. They would have slowed breathing and slowed heart rate (bradycardia). It was almost like a play dead defense mechanism.
Now, fast forward to higher evolved reptiles like crocodiles and some turtles and we start to see evidence of a split in the vagus nerve. This began to happen because these animals were becoming more active and metabolically demanding. If you tried to slow down bodily systems during a stress response in these animals it would not end up well for them.
When we get to mammals, we see the complete split of the vagus nerve into the dorsal motor nucleus and the nucleus ambiguous, like we humans have today. Mammals are much more metabolically demanding than any living thing that evolved before them. This split of the vagus nerve into two pathways is what allowed mammals to become so metabolically demanding (running, quick movements, warm blooded) and still have the ability of our Autonomic Nervous System to trigger a stress response to get away from something threatening without shutting down our very metabolically demanding organ systems.
If mammals had maintained the single dorsal motor nucleus pathway of the vagus nerve while evolving higher metabolically demanding organ systems, then when they would have had a stress response that dorsal motor nucleus would have tried to slow the metabolism of the organ systems just like it did in the reptiles and pre reptile animals. The highly metabolically active organ systems of mammals would not tolerate this, and it would likely cause shut down of organ systems and probably death.
Luckily, they did evolve the dual vagus nerve pathway and it works great in most mammals. Dr. Robert Sapolsky, a Stanford neurobiologist, has spent much of his career studying the stress response in mammals. He has found that the dual vagus nerve system in wild mammals works very well (he outlines this in his book Why Zebras Don’t Get Ulcers quite nicely).
When a mammal is not in a threatening situation (nothing is trying to kill and eat it or its young) then it is perfectly calm and functioning in its parasympathetic state. However, if a threat does present itself then it has a useful, and often times lifesaving, sympathetic response to either fight off or flee the threat. The newly evolved nucleus ambiguous aspect of the mammalian vagus nerve allows it to have this stress response and increase in metabolic demand without the organ shut down of the dorsal motor nucleus.
The most curious thing Dr. Sapolsky observed was that when wild mammals get away from a threat, if they get away, then they fall right back into the parasympathetic. This is the way it is supposed to work and wild mammals use it well. However, we see a very different stress response and stress recovery pattern in us modern humans.
Humans are the only species that have the complex thought processes that we do. We can literally think ourselves into a stress response without anything life-threatening actually happening. Dr. Sapolsky says it well, “mobilizing energy while sprinting for your life helps save you. Do the same thing chronically because of a stressful thirty-year mortgage, and you’re at risk for metabolic problems like diabetes and high blood pressure.”
Between our evolved stress response, our high level of complex thinking, and the unnatural stress of modern civilization, we have created quite the mismatch. When we experience chronically high levels of stress it can decrease the tone of the nucleus ambiguous aspect of our vagus nerve. At this point our body resorts back to the older evolved dorsal motor nucleus, the one that slows metabolism of organs.
In health circles you may have heard about stimulating your vagus nerve. This is the idea that we can do things that will put ourselves into a parasympathetic state by stimulating the nucleus ambiguous aspect of our vagus nerve. People do this to combat the stress of our modern world.
Our modern-day stresses create imbalance in our mammalian ANS. ANS imbalance can lead to prolonged elevated cortisol and that has been linked to high blood pressure, insulin resistance, sexual dysfunction, and chronic inflammation. (5,6) ANS imbalance has also been linked to cardiovascular issues, most notably heart attacks. (1)
This makes sense if you think about it. If the consequence of over stimulating the dorsal motor nucleus in older evolved animals was slowing of metabolism in organ systems, and if we allow the stress of modern day to create an imbalance that makes us more reliant on the dorsal motor nucleus aspect ofour vagus nerve then we could see slow down of an organ like the heart. A part of it could even shut down.
In Part 2, we discussed how when we experience chronic or acute stress, and we are not well fat adapted, that this can cause the heart to move away from burning its preferred fuel source of fat and start to burn glucose instead. In Part 1, we discussed how if this is acute enough it can lead to surges in lactic acid build up that can eventually cause heart tissue death.
Luckily, there are many things we can do to stimulate the nucleus ambiguous aspect of the vagus nerve to rebalance our ANS and prevent heart attacks. Exposure to nature (7), loving relationships (8,9), community (10), and economic security (11) have all been shown to decrease heart attacks. They do this by stimulating ANS balance. However, there is one aspect to rebalancing the ANS that not many people are talking about. It is has everything to do with an animal-based diet.
Remember when I stated above that the ANS is the system that monitors our external environment and tell us if it is safe or threatening. Most people think of our external environment as outside our body, and it is, but this external environment also includes the tube that is our digestive system. Our digestive tract is an external environment that is sealed off from the inside of our body and only what our digestive system decides to let in gets in.
I believe that it is no mistake that our emotion/stress feeling organ, the heart, and our most connected to our external environment organ, the digestive system, are heavily innervated by the vagus nerve. This begs the question of how what we eat affects our ANS balance, and eating plants is not helping us in this regard.
It turns out that plants defend themselves from getting eaten. Animals can fight back or run away but plants can’t. Therefore, they defend themselves in other ways. These ways are making toxins to discourage animals from eating them and there are many toxins made by plants. (12) Some plants are more toxic than others but every plant that exists, even the ones we humans eat, has a toxic component to it. This is why humans can’t eat most plants that exist, but others, the “edible” ones, we can tolerate because of their lower toxicity. But all plants have toxins. Common ones are lectins, phytic acid, oxalates, and tannins.
Our ANS, though the vagus nerve, is monitoring our emotional state to get clues to whether we are in a safe or threatening situation. Likewise, our ANS, also through the vagus nerve, is monitoring our gut to interpret if we are in a safe or threatening environment. (13) What better way to tell our brain we are in an unsafe environment than to eat foods that expose us to toxic substances.
It is well known that many antinutrients in plant foods are aggravating to the lining of our guts and can even cause intestinal permeability or leaky gut. This is especially true of gluten (14), found in grains, and solanine (15), found in nightshade vegetables (potatoes, tomatoes, eggplant, peppers). I don’t see our vagus nerve communicating signals of “safe” to our ANS when we are eating plant toxins that poke holes in our gut lining. That seems like a reason to communicate that we are in an unsafe environment. In fact, irritable bowl syndrome, which these plant toxins can cause, has been link to abnormal vagus nerve function. (16)
Further, one study in rats showed that lectins (a plant toxin found in grains, legumes, and many plant foods) could be transported from the digestive system to the brain vis the vagus nerve (17). The study suggested this was a potential mechanism of development of Parkinsons’s Disease. Again, what better way to tell your brain you are in an unsafe environment that surrounding the vagus nerve with plant toxins.
Scientists have even named the transport of these toxins through nerves as “suicide transport” because once the toxin gets to where it’s going it destroys the nerve connection of the nerve it was traveling on (18). It is not hard to imagine that destroying nerve endings of the vagus nerve will lead to dysfunction of the ability of the ANS to do its job of telling us if we are in a safe or threatening environment.
There are other studies that show that various plant toxins in plants commonly eaten by humans can disrupt different aspects of the nervous system. (19,20,21) All of these are direct effects of these plant toxins on the nervous system and therefore they affect the ANS signal to the heart. As we have illustrated, an imbalance in the ANS is a primary cause of heart attacks. Therefore, anything that disrupts normal function of the ANS can be seem as steering us more toward the conditions in which one would suffer a heart attack. We know that plants have some detrimental effects on our nervous system because anecdotally, there are many cases of neurologic and psychiatric ailments getting better by converting to and animal-based diet. (22)
It has even been argued that plants are survival foods and we evolved to be able to tolerate them so that in times of starvation we could survive on them until we found animal food. Could it be that when we ate plants the plant toxins triggered our ANS to tell our body we must be in a stressful starvation situation? This could have kept us in a fight or flight state that heightened our senses and therefore increase the likelihood of us finding and killing our next animal meal.