The biological effects of fasting and hidden psychological benefits
Explore the surprising psychological benefits of fasting—from dopamine resets to reduced anxiety, and how going without food might actually feed your mind and improve mental clarity.
Imagine a desert father in early Christianity, a Muslim family gathered at sundown during Ramadan, monks in a Japanese Zen monastery during sesshin retreats, and a tech entrepreneur in San Francisco. What do they have in common? They all willingly go without food and willingly participate in one of humanity's oldest experiments in self-regulation, and modern science is finally catching up to what they might be discovering
For centuries, fasting or food restriction was woven into religious ritual and survival necessity. Today, it’s sold as a biohack. But beneath the trendiness and the theology, something remarkable happens when we stop eating: the body begins to heal itself, and the mind starts to change.
So the question is not just “What happens to our health when we fast?” but also “What happens to our sense of self?”
For several years, I've been delving into the research on fasting for my own benefit, as well as to explore its impact on mental health. The findings challenge my fundamental assumptions about hunger, willpower, and nourishment.
What the Body Does When It’s Not Fed
Let's explore what actually happens when you stop eating. We'll start with biology, because the body is usually the first to protest when we skip a meal. Within hours of fasting, blood sugar falls and insulin drops. This signals the body to switch fuel sources—from the quick-burning match of glucose to the steadier flame of stored fat. As fat breaks down, the liver produces ketones, which are surprisingly efficient brain food.
At the same time, cells take advantage of the break. They shift into repair mode, recycling damaged proteins and sweeping out cellular junk in a process called autophagy. Think of it as your body finally getting around to spring cleaning—except the clutter isn't in your closet, it's inside your neurons and tissues.
If the body treats fasting as a chance for housecleaning, the brain treats it as an upgrade. When glucose runs low and ketones take over, neurons don't panic—they actually thrive. Ketones provide a steadier, more efficient fuel, which is why many people report sharper focus, clearer memory, and a surprising sense of calm after the initial hunger pangs pass.
In short: fasting is not just about deprivation. It's about activation—switching on ancient survival programs that our constantly-fed modern lives rarely allow to run.
Dr. Alan Goldhammer, founder and director of the TrueNorth Health Center, has overseen the reversal of chronic illnesses in more than 25,000 people through medically supervised water-only fasting. Having spent 40 years supervising therapeutic fasts, Dr. Goldhammer explains that during the process, the body becomes a "fat-burning machine" by shifting from glucose to stored fat as its primary fuel source.
This metabolic shift isn't just about chemistry; it's about survival programming that has been hardwired into us for millions of years. Our ancestors regularly faced food scarcity, and those who could think clearly, make good decisions, and remain emotionally stable while hungry were the ones who survived long enough to become our great-great-grandparents.
The science backs this up beautifully. Fasting stimulates the production of a protein in nerve cells called brain-derived neurotrophic factor, or BDNF, which plays critical roles in learning, memory, and the generation of new nerve cells in the hippocampus. Think of BDNF as miracle grow for your brain—and the ketone body β-hydroxybutyrate produced during fasting is believed to serve as a signaling molecule that triggers this neuroplastic response.
This explains why many people report increased mental clarity during fasts. Your brain literally gets better fuel (ketones are more efficient than glucose), while simultaneously ramping up the molecular machinery for learning and memory formation.
The Inflammation-Mood Connection
Here's something that blew my mind from Goldhammer's research: most people walking around have about 20 pounds of excess adipose tissue, with roughly 2 pounds being visceral fat—the inflammatory kind wrapped around your organs. This isn't just about fitting into jeans; this visceral fat is "giving off inflammatory products that's causing heart disease, cancer, diabetes," and here's the psychological kicker—it's also affecting your mood and cognitive function.
When fasting specifically targets this inflammatory fat, people often report improvements in depression and anxiety. This aligns with emerging research showing that many mental health conditions have an inflammatory component. Chronic low-grade inflammation can disrupt neurotransmitter synthesis, impair neuroplasticity, and even shrink brain regions involved in mood regulation.
The beauty of fasting is its precision: it mobilizes visceral fat preferentially over other fat stores, essentially targeting the most metabolically harmful tissue. As this inflammatory burden decreases, many people experience what researchers describe as improved "cognitive-affective" functioning—clearer thinking paired with better emotional regulation.
The Clinical Evidence: Beyond Anecdotal Reports
Perhaps the most compelling evidence comes from recent clinical research. A systematic review and meta-analysis of randomized controlled trials found that fasting groups had significantly lower anxiety (b = −0.508, p = 0.038) and depression levels (b= −0.281, p = 0.012) compared to controls, without increased fatigue. We're not talking about marginal improvements here—these are clinically meaningful reductions in mental health symptoms.
Even more intriguingly, a cross-sectional study of patients with major depressive disorder found that fasting improved cognitive-affective sub-scores in MDD patients with moderate/severe symptoms that had not responded to prior therapy. This suggests fasting might offer hope for treatment-resistant depression, potentially working through pathways that traditional antidepressants miss.
The mechanism appears to involve differential changes in BDNF levels—that same brain-boosting protein we discussed earlier. When your brain increases BDNF production during fasting, you're not just getting sharper thinking; you're potentially rewiring neural circuits involved in mood regulation and stress response.
But here's where the research gets nuanced. Some studies report that short-term fasting can initially increase negative emotions like depression, anxiety, anger, and irritability while decreasing positive emotions and vitality. This suggests there's a critical adaptation period where your brain is essentially learning to function differently—much like the temporary discomfort you might feel when starting an exercise program.
The Dopamine Reset Nobody Talks About
Perhaps the most profound psychological effect of fasting is what happens to your reward system. We live in what Goldhammer calls a world "designed to make you fat, sick, and miserable," where we're constantly bombarded with hyperpalatable foods engineered with salt, oil, and sugar—his "SOS" chemicals that hijack our natural satiety mechanisms.
When you fast, something remarkable happens to your taste neurons. Foods that seemed bland before suddenly burst with flavor. An apple tastes like candy. Plain vegetables become satisfying. This isn't just metaphorical—fasting literally resets your dopamine sensitivity, breaking what Goldhamer calls "the dietary pleasure trap."
I think of this as exposure therapy for the modern world. Just as we might gradually expose someone with a phobia to their feared object, fasting gradually exposes us to the discomfort of wanting without immediately gratifying. The result? Increased tolerance for discomfort and stronger self-regulation skills that extend far beyond food choices. Research shows that intermittent fasting upregulates protein synthesis and neuroplasticity, enhancing learning and memory—changes that support better decision-making and impulse control.
The Gut-Brain Conversation Gets a Reboot
One of the most exciting areas of research involves fasting's effect on the gut microbiome. When you fast, you essentially "wipe out a lot of the bacteria in your gut, including the bad ones, but also some good ones," as Goldhammer explains. But here's the opportunity: careful refeeding allows you to "reestablish that normal microfloral balance."
This gut reset has profound implications for mental health. We now know the gut produces about 90% of our serotonin, and an imbalanced microbiome is linked to anxiety, depression, and cognitive fog. Fasting offers a chance to hit the reset button on this crucial mind-body connection.
The Shadow Side: When Fasting Goes Wrong
Let me be clear—fasting isn't a psychological panacea. For individuals with a history of eating disorders, fasting can be triggering and dangerous. The same psychological mechanisms that make fasting beneficial—increased self-control, delayed gratification, tolerance for discomfort—can become compulsive and harmful when taken to extremes.
I've also seen people use fasting as a form of self-punishment or as a way to avoid dealing with difficult emotions. The key is intention: Are you fasting to enhance your relationship with yourself and food, or are you using it to escape, control, or punish?
Beyond Biology: The Meaning-Making Machine
What fascinates me most is how fasting seems to activate our innate meaning-making capacity. Across cultures and throughout history, voluntary food restriction has been associated with spiritual insight, emotional clarity, and personal transformation. There's something about voluntarily embracing discomfort that shifts our psychological relationship to difficulty itself.
Goldhammer notes that many of his patients are motivated by "pain, disability, and fear of death"—they're willing to fast because they're desperate for change. But the psychological benefits extend beyond crisis management. Healthy people who fast preventively often report that it's a "forced period of rest and introspection," offering mental space that's increasingly rare in our hyperconnected world.
The Practical Psychology
If you're curious about fasting, start small and pay attention to your psychological responses. Notice when you feel truly hungry versus when you're eating out of boredom, stress, or habit. Observe how your mood, energy, and mental clarity change during different eating patterns.
Remember: fasting is as much a psychological practice as a physical one. You're not just changing when you eat; you're changing how you relate to desire, discipline, and discomfort. That's powerful stuff.
More Than Just Not Eating
In the end, fasting offers us a unique window into the intimate connection between our bodies and minds. It's a practice that simultaneously challenges our biology and psychology, offering insights that extend far beyond weight loss or health metrics.
The question isn't whether fasting is right for everyone—it's not. The question is: What might you discover about yourself when you learn to sit with hunger instead of immediately feeding it? In a world that profits from our immediate gratification, that kind of self-knowledge might be the most radical act of all.
What conversation might your body and mind have if you gave them the space to talk?