Understanding Our Body as a System
- Erin Kuta
- Feb 18
- 6 min read
Updated: May 27
Embodiment in Nutrition Counseling Series - Part 3
by Erin Kuta, MPH, RD, LDN
Consider some of these common eating scenarios:
You eat a full lunch and twenty minutes later, you’re genuinely hungry again.
Your appetite disappears during the day, then shows back up the moment you finally sit down at night.
You finish a meal and don't remember eating it. A bummer.
Food sounds good until it’s in front of you, and then suddenly you can't stomach It.
These experiences can feel frustrating and confusing, almost like your appetite is working against you.
However, when we step back and look at the bigger picture, these patterns can start to make more sense. Our body functions as an interconnected system, and changes in appetite are information about how that system is responding.
How your body systems talk to each other
Three communication networks can help explain shifts in appetite:
The HPA axis, which manages your stress response.
The vagus nerve, which connects your brain and digestive system
The enteric nervous system, the gut's own neural network.
The HPA Axis: Your Stress Response System
The HPA (hypothalamic-pituitary-adrenal) axis is your body's main communication network coordinating signals between your brain and your adrenal glands (Tsigos & Chrousos, 2002). When stress increases, cortisol (your primary stress hormone) rises. This cortisol shift alters appetite-related hormones like ghrelin (which promotes hunger) and leptin (which increases feelings of fullness).
This is why, under stress, your appetite can shift in either direction. Some people find it increases: sudden cravings for comfort foods, eating past fullness, feeling depleted despite eating more. Others find it drops almost entirely, forgetting to eat, feeling no hunger, or having to force themselves through meals. The hormonal mechanism behind both is the same: elevated cortisol altering ghrelin and leptin (Adam & Epel, 2007). Some people tend toward one direction; many move between them, sometimes within the same week.
The Vagus Nerve and Your Nervous System States
Your gut and brain are also in constant conversation through the vagus nerve, the longest nerve in the body. It carries messages in both directions between your brain and organs, including our digestive system. A part that surprised me when I first learned about the vagus nerve: about 80% of those signals travel from your body to your brain (Berthoud & Neuhuber, 2000). In other words, your body has a lot to say! That ongoing traffic influences digestion, mood, immune responses, and how you handle stress and emotions (Cryan & Dinan, 2012).
The vagus nerve is also part of how your nervous system shifts between different states throughout the day (Porges, 2011). You might recognize some of these:
Rest and digest: When you feel safe and relatively calm, ventral vagal pathways support smoother digestion. You can taste your food, notice more subtle hunger and fullness cues, and feel your body settling. This is when your body can more easily absorb nutrients and send clear signals about what it needs.
You know this feeling: sinking into the couch at the end of the day. An exhale. Perhaps this feels rare with our modern pressures. Sometimes it means actively reducing stimulation: turning off your phone, stepping outside, breathing slowly, or getting support that helps your body regulate, whether that's body-based (massage, yin/restorative yoga, acupuncture), mind-based (therapy, coaching), or relational (a friend who truly gets it).
Fight or flight: When you’re stressed, anxious, or perceiving threat, sympathetic activation takes the lead and your body prioritizes survival. Digestion can slow or pause, blood flow shifts away from the gut, and appetite may drop or feel “jittery” and unreliable. You might know you need to eat but feel unable to because your body is focused on immediate safety, not processing lunch.
Think about how you feel before public speaking: heart pounding, water bottle glued to your hand (SO thirsty!), running to the bathroom every five minutes, abdomen alive with sensation, but zero room for food. Or the lower-grade version with chronic stress: morning appetite destroyed by an early alarm and a chaotic commute, relying on coffee to function, appetite finally showing up at night when you're trying to wind down.
Freeze or shutdown: In overwhelming or prolonged stress, dorsal vagal pathways can dominate and you may feel numb or disconnected. Hunger and fullness cues become muted or distant. You might go hours without noticing you haven’t eaten, or eat on autopilot without much satisfaction.
Everything feels slow as molasses. Your body demands stillness. Food decisions feel impossible, and honestly, you don't really care what you eat as long as it's easy. Drive-through Dunkin' wins over making lunch. Not because you don't "value your health," but because your nervous system is conserving every bit of energy it has left. Caring requires capacity.
The Enteric Nervous System: Your Gut's Own Brain
Where are all those upward body-to-brain signals coming from? A significant source is the enteric nervous system, a vast network of roughly 500 million neurons lining your digestive tract (Furness, 2012). It's often called the "second brain" because it coordinates digestion without waiting for instructions from above.
A fun fact to share at your next social gathering: the enteric nervous system produces an estimated 90-95% of the body's serotonin (Mawe & Hoffman, 2013). Most people think of serotonin as a brain chemical, but the majority of it lives in your gut.
This is why stress and anxiety can show up so clearly in the body. That includes the butterflies before something nerve-wracking or the nausea when you're overwhelmed. You may have falsely heard that this is "all in your head," but that's not the full story. What's happening is the enteric nervous system responding in real time to your nervous system state. In other words, your gut feelings are physiologically valid and incredibly important to listen and respond to with care.
What I'm noticing
Right now, most clients I work with are managing some form of chronic stress. It's the accumulated stress of work demands, family dynamics, relationship strain, financial pressure, physical illness, sleep disruption, and the constant pull of screens and information. Diet culture adds its own layer with the constant pressure to meet narrow standards of appearance and wellness. Add political uncertainty, threats to safety and rights, and ongoing exposure to crisis. Your stress response, which is designed for short-term threats, is running continuously.
Your body feels all the stress, regardless of the source, which can inevitably affect appetite, digestion, and food choices. It can suppress hunger or intensify cravings. For many people, food becomes a means of comfort, distraction, or regulation when other resources feel depleted.
When we look at eating patterns through this Interconnected lens, they start to make sense.
Hungry 20 minutes after lunch? This could be about nervous system state during eating, inadequate intake over previous days, and/or needing more food than that meal provided.
Appetite disappearing, then roaring back at night? This could be fight-or-flight suppressing appetite during the day, under-eating that your body compensates for later, and/or finally feeling safe enough to eat once you slow down.
Don't remember eating? This could reflect eating in survival mode, multitasking during the meal, and/or dissociation preventing presence with food.
Food suddenly unappealing? This might reflect a shift in nervous system state, blood sugar dropping while you waited, and/or realizing the food doesn't match your actual needs.
In summary, your body is adaptive and protective, working hard to carry you through life. Understanding it as an interconnected system gives you more room to notice what's actually happening: Oh, my appetite is gone. I've been activated since my 7am commute, so that makes sense. When we combine this kind of body awareness with self-compassion, self-care decisions can start to be shaped by what our nervous system actually needs, rather than by an imagined standard.
Key Takeaways
Appetite changes under stress aren't arbitrary. They're driven by three interconnected systems: the HPA axis, the vagus nerve, and the enteric nervous system.
Stress can shift appetite in either direction. Elevated cortisol alters ghrelin and leptin, which can increase cravings and eating, or suppress hunger almost entirely. Both are normal stress responses.
Your nervous system state (rest and digest, fight or flight, freeze) directly shapes your capacity to eat, digest, and notice hunger and fullness cues.
Your gut has its own nervous system. The enteric nervous system produces an estimated 90–95% of the body's serotonin, which is why stress and anxiety show up so clearly in the stomach.
Understanding what state you're in changes the question from what's wrong with me to what does my body need right now, given where it actually is.
References
Adam, T. C., & Epel, E. S. (2007). Stress, eating, and the reward system. Physiology & Behavior, 91(4), 449–458.
Berthoud, H. R., & Neuhuber, W. L. (2000). Functional and chemical anatomy of the afferent vagal system. Autonomic Neuroscience, 85(1–3), 1–17.
Furness, J. B. (2012). The enteric nervous system and neurogastroenterology. Nature Reviews Gastroenterology & Hepatology, 9(5), 286–294.
Mawe, G. M., & Hoffman, J. M. (2013). Serotonin signalling in the gut: Functions, dysfunctions and therapeutic targets. Nature Reviews Gastroenterology & Hepatology, 10(8), 473–486.
Porges, S. W. (2011). The Polyvagal Theory: Neurophysiological Foundations of Emotions, Attachment, Communication, and Self-Regulation. W. W. Norton & Company.
Tsigos, C., & Chrousos, G. P. (2002). Hypothalamic-pituitary-adrenal axis, neuroendocrine factors and stress. Journal of Psychosomatic Research, 53(4), 865–871.
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