The body is hardwired with a number of primitive reflexes. These produce unconscious responses, which are a reaction of the autonomic nervous system. For most of us, food is something that has an emotional connection, after all, as the proverb goes: the way to a man’s heart is though his stomach.
Picture this: each time you eat, your heart starts racing, you start sweating profusely, and when you look in the mirror, your face is flushed bright red. By working with rare autonomic diseases we are able to understand how involuntary reflexes are affected in different neurological disorders. In familial dysautonomia, primitive reactions of the body can become highly exaggerated.
In the most recent issue of Experimental Physiology, researchers at the Center published a paper describing the autonomic reactions to eating. They show how blood pressure, heart rate, and breathing increase abruptly in patients with familial dysautonomia when eating. This explains why they often show signs of an autonomic reaction during meals.
The reaction occurs instantaneously at the exact moment chewing starts. It is independent of stomach distention and doesn’t occur when food is put directly into the stomach via a tube. The same reaction appears when chewing gum (without swallowing). The reaction is short-lived and subsides the moment the food is swallowed. It doesn’t appear to be dependent on what patients are eating, and occurs also in those following a tyramine-free diet. It happens to a lesser extent in healthy people, but is quickly dampened to prevent it from escalating further.
This leaves one obvious question: why do we get an excitatory “flight of fight” autonomic response when we eat? Watch animals: many times you will see a similar response. They have signs of autonomic activation – and can protect their food aggressively. This suggests that we all have a primitive hardwired autonomic response to eating. Did it serve an evolutionary advantage in humans? Perhaps it was useful to prepare us to defend our food, a precious biological commodity, at times when it was scarce would certainly be a useful trait.
Not only do the new findings indicate that the connection to a man’s heart probably occurs before the food hits his stomach, they also tell us that this exaggerated chewing gum reaction is a useful way for these patients to quickly raise blood pressure at times when it’s too low.
Fuente Mora C, Norcliffe-Kaufmann L, Palma JA, Kaufmann H. Chewing-induced hypertension in afferent baroreflex failure: a sympathetic response? Exp Physiol. 2015 Oct 4. doi: 10.1113/EP085340. [Epub ahead of print]