Can an Animal-Based Diet Prevent Heart Attacks? - Part 3

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.