A cold plunge is a short, controlled dunk in cold water (around 50 to 59 degrees Fahrenheit) that triggers a strong nervous-system and metabolic response. Research from Dr. Susanna Søberg suggests that about 11 minutes a week, split into 2 to 4 sessions, can support brown fat activity, dopamine, and insulin sensitivity in healthy adults.
The Søberg Principle
Cold exposure is a small, useful kind of stress called a hormetic stressor (a stressor in low doses that triggers helpful adaptation). Using the Søberg Principle (ending your shower with cold), we can support insulin sensitivity and a steadier dopamine baseline.
You have probably seen the social-media clips of people sitting in ice chests. The internet loves the spectacle, but the physiology underneath is real. Cold exposure is one of the strongest natural ways to change dopamine (drive and focus) and to push your body into metabolic flexibility (the ability to switch clearly between fuels).
At Fishtown Medicine, we do not view cold exposure as a toughness test. We view it as a lever for changing your neurochemistry and your fuel handling.
What Does Cold Actually Do to Your Body?
Most adults have low levels of brown adipose tissue (BAT, the heat-burning fat between your shoulder blades). White fat stores energy. Brown fat burns glucose to make heat. Cold exposure helps wake brown fat back up.
- White fat. Stores energy.
- Brown fat. Burns sugar and fatty acids to make heat (thermogenesis).
When you step into the cold, your body fires up brown fat to keep your core warm. That process pulls glucose out of the bloodstream and, over time, can improve insulin sensitivity. Dr. Susanna Søberg's work in Copenhagen suggests that about 11 minutes of cold a week is the sweet spot for this metabolic change.
How Does Cold Exposure Change Brain Chemistry?
Dopamine. Cold immersion has been shown to raise dopamine by up to 250%. Unlike a stimulant crash, the dopamine bump from cold tends to last for hours, supporting steady focus and mood.
Norepinephrine. This alertness chemical also spikes during cold exposure. It helps lower inflammation and clears the brain fog that many of our patients describe after a long Philly winter.
What Does the Beginner Protocol Look Like?
You do not need a $5,000 tub. You need consistency.
The Fishtown Strategy (Beginner)
- Shower as usual. Take your normal warm shower.
- Switch to cold. Turn the knob fully cold for the last 30 seconds.
- Breathe. Your body will want to gasp because of a fight-or-flight reflex. Force calm, slow nasal breathing instead. This trains your nervous system to stay composed under stress.
- Build slowly. Add 10 seconds each week until you can tolerate 2 to 3 minutes.
The Søberg Principle
- Total time. About 11 minutes per week, split into 2 to 4 sessions.
- End on cold. Skip the hot rinse afterward and let your body rewarm on its own. The energy your body uses to rewarm is part of the benefit.
Cold vs. Coffee: How Do They Compare?
Fishtown Medicine
A 90-minute conversation with Dr. Ash. A written plan you can actually follow.
Cold gives you a different kind of energy from caffeine.
| Goal | Coffee | Cold Plunge | Why They Differ |
|---|---|---|---|
| Morning energy | Blocks adenosine receptors (masks sleepiness). Can cause jitters and a crash. | Raises dopamine and adrenaline. Builds real alertness. | Smoother taper, much lower crash risk. |
| Mood and focus | Mild boost. | Strong, sustained dopamine rise. | A steadier neurochemical change. |
| Inflammation | Context dependent. | Body-wide anti-inflammatory effect through norepinephrine. | Useful for recovery and joints. |
Guidance from the Clinic
We have your back. At Fishtown Medicine, the goal is not to order tests and hand you a number. We interpret, explain, and advocate. You should feel like you have a Chief Medical Officer in your corner.
> "Dr. Ash, I hate the cold."
I hear this often. My take is that the discomfort is actually the mechanism of action.
Overcoming the initial flinch builds mental resilience. In my experience, the carryover effect is strong. If you can breathe calmly while stepping under freezing water at 6 AM, you are far better equipped to handle a stressful email or a crisis at 10 AM.
Actionable Steps in Philly
Winter in Philly is a free entry point for cold exposure.
- Underdress on purpose. When walking the dog in January, try a light sweater instead of a heavy parka. Allow your body to shiver. Shivering releases succinate, a chemical signal that helps activate brown fat.
- Use the tap. Philly tap water in winter is legitimately cold (often under 50°F). For your nervous system, that is essentially the same as a dedicated plunge tub.
- Find your community. If you need accountability, join a local polar plunge group at the Jersey Shore or look for outdoor swim clubs around the city.
Let's figure this out together.
Scientific References
- Søberg S, et al. Altered brown fat thermoregulation and enhanced cold-induced thermogenesis in young, healthy, winter-swimming men. Cell Rep Med. 2021;2(10):100408.
- Srámek P, et al. Human physiological responses to immersion into water of different temperatures. Eur J Appl Physiol. 2000;81(5):436-442.
- Buijze GA, et al. The effect of cold showering on health and work: a randomized controlled trial. PLoS One. 2016;11(9):e0161749.
- Šrámek P, et al. Norepinephrine, dopamine, and immune response to cold-water immersion. Eur J Appl Physiol. 2000.
- Roberts LA, et al. Post-exercise cold water immersion attenuates acute anabolic signalling and long-term adaptations. J Physiol. 2015.
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