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Summary
On episode 218 of 40+ Fitness, Coach Allan sits down with Jo Marchant, a New York Times bestselling science journalist and author of Cure: A Journey into the Science of Mind Over Body.
Jo explains that placebos aren’t just imagined relief. They trigger measurable biological changes in the brain, working through many of the same pathways as real drugs.
The conversation moves through fatigue, high-intensity interval training, and heart rate variability, all tied together by the idea that the brain plays a much bigger role in physical performance and healing than most people realize.
Links
- https://jomarchant.com
Key Takeaways
- Placebos trigger real, measurable changes in the brain. When someone responds to a placebo painkiller, their brain releases endorphins, the same mechanism opioid painkillers work through. Parkinson’s patients who respond to placebo release dopamine, the exact neurotransmitter they’re lacking. Even fake oxygen at altitude reduces symptoms of altitude sickness through a real drop in brain chemicals called prostaglandins.
- Honest placebos can work even when people know it’s a placebo. Recent trials in irritable bowel syndrome, depression, chronic low back pain, migraine, and ADHD show improvement even when patients are told upfront they’re taking a placebo. Jo says part of the effect may come simply from being cared for, which signals to the brain that a crisis is over. Being told that pain is modulated by the brain may also be empowering on its own.
- Fatigue is imposed by the brain well before the body actually runs out. Using Olympic runner Mo Farah as an example, Jo explains that exhaustion is a psychological limit the brain sets in advance of any real physical damage to the muscles, based on how severe it judges the threat to be. That’s why an athlete can look completely spent crossing the finish line and then be jogging around the track moments later.
- High-intensity interval training works partly by retraining the brain’s safety limit. Pushing close to your limit and then recovering teaches the brain that going that far was fine, so it relaxes the limit slightly the next time. Over repeated sessions, that coaxes the brain into releasing more resources and letting you go further.
- Confidence and expectation carry over into strength training. Allan draws the parallel to a lifter grinding through a tough final rep: knowing you got there once tells your brain it’s safe to go further next time. Getting your brain out of the way of doubt and fear often produces faster progress than the physical training alone.
- The vagus nerve calms the body down after a stress response. It’s the core of the parasympathetic nervous system, acting as a counterweight to the fight-or-flight sympathetic response by slowing the heart and dampening inflammation. Chronic inflammation from constant stress can worsen autoimmune disease, weaken infection resistance, and disrupt wound healing, so a stronger vagus nerve response matters for long-term health.
- Slow breathing measurably boosts heart rate variability and vagal tone. Breathing in and out on roughly a five-second cycle lines up two natural heart rate cycles (one tied to breathing, one tied to blood pressure) so their peaks and troughs stack, raising overall variability. People with stronger vagal tone have a lower risk of heart disease and show benefits like better stress flexibility and lower risk of anxiety and depression.
- Meditation and breathing techniques work through the body as much as the mind. Jo notes that most of the signal traffic on the vagus nerve runs from body to brain, not the other way around, which is why calming the body through slow breathing is often a more efficient path to a calmer mind than trying to calm the mind directly.
“It’s not absolutely dependent on the physical state of your body. Your brain is playing a role, and therefore your beliefs, hopes, attitudes, expectations can play a role in that, we have some control.”
Jo Marchant