Metabolism 101

How fight-or-flight heritage helps and hinders us today

VIV Research
September 20, 2021

Think about the last time you were driving and were about to hit another car. Ideally, you slammed on the brakes or swerved out of the way, and avoided a crash. Your lightning-quick actions came courtesy of your body’s fight-or-flight mechanism, a response to deal with perceived threats.

On the plus side, fight-or-flight allowed you to stay safe. On the down side, think about how you felt immediately after the incident. Your heart was racing, your muscles were tense, and you had an adrenaline rush. You were on edge. Even though the threat of a crash had passed, your body was still primed for action.

It doesn’t take an impending collision to trigger this response. Note the words “perceived threats” above. There’s often a mismatch between your body going into fight-or-flight mode and the event that triggered it. And that can have serious consequences for your health.

Before we examine those health consequences, let’s step back for a moment and look at why you have the fight-or-flight mechanism.

It helped us survive

This innate reaction to stress evolved over millions of years to energize and protect us when our safety is at risk. It’s triggered almost immediately by anxiety or fear. The physiological changes it induces enhance your physical strength (“fight”) and increase your speed and stamina (“flight”). Fight-or-flight allowed our ancestors to deal with predators, other humans, natural disasters, and other threats to a long Stone Age life.

In modern life, most of our perceived threats are psychological. Even the physical ones, such as trying not to smash into the distracted driver in front of you, don’t merit full-on readiness to fight or flee. Both types are usually what we might we call micro-threats, brief but frequent events that we react to with a response better suited to deal with true emergencies.

This is where the health problems can start. Among the hormonal reactions to a perceived threat is the adrenaline rush you’re no doubt familiar with. That surge of adrenaline leads to a spike in your blood glucose levels; this is your body’s way of quickly providing the energy needed to handle the threat. If that threat is, say, a hungry predator, great—you’ll need that blood glucose boost to do battle or escape. But if the threat is a two-second encounter with another driver, or an argument with your partner, or anxiety about a work presentation, not so great. You get that jolt of energy, but there’s no life-or-death situation to apply it to. Your adrenaline and blood glucose levels remain elevated even after the situation has passed. Modern life is such that you might encounter several micro-threats a day, each causing an unhelpful spike (and eventual crash) in your blood glucose levels. As far as your body is concerned, this boom-and-bust energy cycle wreaks just as much havoc whether it’s caused by stress or a poor diet.

Elevated levels of another key hormone, cortisol, are also part of fight-or-flight. When your cortisol levels are chronically spiked, you’re more likely to crave food, and you’re more likely to store whatever food you as belly fat.

Regularly monitoring your blood glucose levels can give you insight on the types of situations that unhelpfully trigger your fight-or-flight response. Meditation, relaxation exercises, and other emotion-regulation techniques can then help you to better deal with these stressors, and thereby be healthier.