Overview of Essentials: Cold & Heat Exposure for Metabolic Health with Dr. Susanna Søberg
This episode revisits Dr. Susanna Søberg’s research on how deliberate cold exposure and sauna use affect metabolism, brown fat, insulin sensitivity, and inflammation. The central message is that brief, repeated exposure to temperature stressors can act like exercise for your cells—building resilience, improving metabolic health, and supporting cardiovascular function. The discussion emphasizes that the benefits come not from comfort, but from controlled, tolerable discomfort and the body’s adaptive response to it.
Key Takeaways
- Cold exposure should feel uncomfortable, not pleasant. A mild “cold shock” response—faster breathing, gasping, and sympathetic activation—is a sign the stimulus is strong enough.
- Cold water is more potent than cold air because it activates more cold receptors across more of the body.
- Brown fat is a major target of cold exposure. It helps generate heat and supports metabolism by burning glucose and fatty acids.
- Shivering is not necessarily bad. It is part of the thermoregulatory response and can contribute to metabolic adaptation as long as you do not become dangerously cold.
- Heat and cold both act as hormetic stressors. In small doses, they can improve cellular resilience through heat shock proteins and related adaptations.
- Ending on cold can be advantageous because your body must continue generating heat afterward, extending the metabolic effect.
- The benefits do not require extreme exposure. Short sessions, done consistently, appear sufficient.
How Cold Exposure Works
Immediate physiological response
Cold receptors in the skin send signals to the hypothalamus, which responds by activating the sympathetic nervous system and releasing neurotransmitters such as norepinephrine. This helps stimulate brown fat and preserve core temperature.
Brown fat and shivering
- Brown fat acts like the body’s “first responder” to cold.
- Shivering adds another layer of heat production through muscle activity.
- These systems work together to prevent hypothermia and restore temperature balance.
The “afterdrop”
A key explanation in the episode is the afterdrop:
- In cold water, blood vessels constrict to protect core organs.
- When you get out, vessels reopen.
- Cold blood from the skin returns to the core.
- Core temperature drops further, which can trigger shivering.
Findings From Dr. Søberg’s Research
Winter swimmers vs. controls
In her study comparing adapted winter swimmers to controls, the cold-adapted group showed:
- Better insulin sensitivity
- Lower insulin release
- Faster glucose clearance
- Lower blood pressure
- Lower heart rate
Inflammation markers
The study also measured inflammatory markers and found changes consistent with reduced inflammation over time, including:
- IL-6
- IL-10
These findings support the idea that cold and heat exposure may help counter inflammatory processes linked to modern lifestyle diseases.
Brown fat growth and adaptation
Repeated cold exposure appeared to:
- Increase brown fat activity
- Improve mitochondrial efficiency in brown fat
- Increase skin vascular adaptation
- Make the body more efficient at maintaining temperature
Practical Protocol Insights
How much cold and heat?
From Søberg’s study, the effective weekly exposure was approximately:
- Cold water: about 11 minutes total per week
- Often broken into 1–2 minute sessions
- Sauna: about 57 minutes total per week
- Often broken into 10–15 minute sessions
You do not need extreme cold
The episode stresses that:
- You do not need to swim for long periods
- You do not need ice-cold water every time
- Even brief exposure to cold air, cool rooms, or a cold hand/face stimulus can activate brown fat
Temperature variation matters
The key principle is moving between warm and cold, not rigidly chasing a specific number. Repeated transitions train the body’s thermoregulatory systems.
The “Søberg Principle”: End on Cold
Dr. Søberg recommends ending cold exposure on cold rather than warming up first and stopping there. Why?
- It forces the body to generate heat on its own
- It keeps brown fat and muscles active
- The metabolic effect continues for hours after the session
- Over time, the body becomes better at producing heat efficiently
Why This Matters for Health
The episode frames cold and heat exposure as tools for improving:
- Metabolic health
- Glucose regulation
- Insulin sensitivity
- Cardiovascular function
- Stress resilience
- Inflammation control
This may be especially relevant in modern life, where people spend more time in temperature-controlled environments and move less, reducing exposure to natural stressors that once helped regulate physiology.
Cautions and Common Sense
- Cold exposure should be challenging but controlled
- Avoid overexposure that could lead to hypothermia
- If you are new to cold training, start small and build gradually
- The goal is adaptive stress, not punishment
Bottom Line
Dr. Søberg’s research suggests that brief, repeated cold exposure and sauna use can act as powerful hormetic stressors that improve metabolic and cardiovascular markers. The main lesson is not to seek suffering for its own sake, but to use controlled temperature stress to train the body—especially by alternating between warm and cold and ending cold when possible.