Dieting and Your Nervous System
Dieting, especially chronic and cycling dieting, can have serious effects on our relationship with food, our energy levels, our hormones, etc. Dieting both affects and is affected by our nervous system more than we often realize, so I decided to dig a little deeper into what the effects are.
There are two halves that make up the nervous system. The central nervous system (CNS) comprises the brain and spinal cord. The peripheral nervous system (PNS) connects the brain with the rest of the body - think nerves carrying messages back and forth from the brain to organs and different parts of the body. The PNS is split up into the autonomic and the somatic nervous system. The somatic nervous system is involved in our skeletal muscles movement. The autonomic nervous system is involved in automatic, regulatory functions and is split up into two parts: the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS).
You may not remember the phrase "sympathetic nervous system" from school, but you probably have heard about what it does: the SNS activation leads to the “fight or flight” response. When the PNS is activated, in contrast, it leads to the complementary “rest and digest” response.
The “fight or flight” activation in the body helps prepare us for a perceived threat. The preparations include increasing pupil size and heart rate, expansion of lungs, release of epinephrine/norepinephrine, and inhibition of the digestive system. These processes help prepare the body for the threat and optimize the parts of the body to protect you from the threat- increased benefit from more oxygen in lungs and decreased benefit in digestion.
The parasympathetic nervous system is the exact opposite of the sympathetic nervous system. Pupils contract, heart rate decreases, and stimulation of the digestive system occurs.
It’s clear that this set of opposing responses would benefit our ancestors for survival. The sympathetic response, however, isn't only triggered by real physical danger. Social anxiety, work stress, and the hunger that you feel when dieting can engage the sympathetic response just as effectively as danger.
This mismatch between stimulus and response can invoke the fight or flight response for many unneeded situations such as giving a presentation at a conference, taking a big test or dieting. It's not just ineffective, it's also bad for your health to keep the SNS response engaged all the time. Fad diets that ignore this reality just set us up for failure.
Dieting keeps us in the SNS response by basically training our bodies that a threat is around. We live in a calorie deficit when we are dieting- our bodies are not properly fueled which signals to our brain that we are entering a famine and once again, survival skills must kick in. Living in this state can cause a lot of stress and anxiety from the constant release of hormones triggering increased blood pressure and heart rate. Cortisol is released to aid in replenishing stored energy used during the “fight or flight” mode. Cortisol can increase appetite so you will eat more to obtain more stored energy. Elevated cortisol and stress can have harmful effects on our health.
It's almost never effective to try to fight through this stress to keep dieting. Trying to ignore a substantial calorie deficit and keep restricting our food intake will just make us even more stressed and anxious, which will just increase the strength of the SNS response. Our bodies end up seeing this as "the famine is getting worse, we need food NOW!" This is why so many people get caught in the vicious cycle of crash dieting and then gaining it all back. Our whole physiology is built to resist the rapid weight loss that these diets are trying to sell us.
It is so much more beneficial for our health to spend more time in the parasympathetic system. Living in the rest and digest state can help us get out of chronic dieting. We can listen to our bodies better in this state, and our bodies give great cues for the food we need to nourish ourselves, and for the rest we need to heal and rejuvenate ourselves mentally and physically. Participating in yoga, meditation, walks, or any movement that allows you to breathe, connect, and slow your mind and breath down is a great way to start taking steps away from dieting and down the intuitive eating path.