The science of ice baths, brown fat and metabolism | Susanna Soeberg, PhD

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In Episode #250, I’m joined by Susanna Søberg, PhD to examine the science of cold water exposure.

“Cold water immersion has a lot of potential as a preventative tool to lower stress and lifestyle diseases.”

Ice baths and other forms of cold water exposure have gained a huge amount of traction in the past few years. With so many people online claiming the profound benefits of this practice, it’s important to return to the science – is cold water exposure safe? What does the science say about the bold health claims? Is brown fat just a buzzword? How do you safely and effectively implement hot and cold exposure into your life? Dr Søberg answers these questions and many more in this three-hour deep dive into cold water immersion.

Dr Susanna Søberg is an internationally leading expert on cold and heat as a stress management tool for physical and mental health. She completed her PhD in metabolism and cold water exposure at The University of Copenhagen, contributing to a deeper understanding of our metabolism and its intersection with our central nervous system. She is the founder of the Soeberg Institute and communicates her knowledge via her online programs, books, SoMe, podcasts, talks, and workshops.

“The body has the ability to get more robust if you expose yourself to some form of stress. And when you do that, the cells get stronger.”

In Episode #250, you will learn about brown fat: what it is, how it’s different from white fat, and how we can activate it. Dr Søberg explains how cold water exposure works on a physiological level, breaking down exactly why it is beneficial. She also shares her recommended weekly cold and hot exposure protocol, and how you can start safely integrating this technique into your lifestyle.

Specifically, we discuss:

  • Intro (00:00)
  • The tradition of winter swimming (01:52)
  • Cold water swimming and activating brown fat (09:44)
  • Dr. Soeberg’s personal experience with cold water bathing (23:13)
  • Funding hurdles and potential benefits of cold water immersion (25:34)
  • Cold water immersion and the body’s response (33:36)
  • Brown fat activation and more physiological responses (40:45)
  • What is brown fat? (45:54)
  • Is brown fat genetic? (55:28)
  • Benefits of activating brown fat (58:32)
  • Winter swimming, sauna, and disease: what the data says (1:01:10)
  • Metabolism and shivering (1:13:01)
  • Brown fat activation and muscle building (1:25:06)
  • Who has more brown fat: Women or Men? (1:36:33)
  • Chronic inflammation, exercise, and more benefits of deliberate cold exposure (1:46:11)
  • Cold water immersion for beginners (2:06:18)
  • The minimum threshold for health benefits using cold and heat (2:15:03)
  • Clothes or no clothes? (2:22:57)
  • Temperature regulation and gender differences (2:26:30)
  • Safety protocols & understanding ice plunging lingo (2:34:08)
  • Outro (2:47:18)

The science of hot and cold exposure is an understudied area, but there are certainly some interesting preliminary findings that suggest these practices could significantly improve our health and quality of life. I hope this conversation with leading expert Dr Søberg helped you better understand how this practice could help you.

To connect with Dr Susanna Søberg, you can find her on InstagramTwitterFacebookTikTok, and LinkedIn. Head to her website,, to learn more about Dr Søberg’s work – including her research and her book Winter Swimming. Friends of The Proof can also receive a 10% discount on her Thermalist course with code SIMONHILL.

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Enjoy, friends.


More about Susanna Soeberg

Dr. Susanna Soeberg is an international leading expert in cold and heat as stress management for physical and mental health. She did her PhD in metabolism at The University of Copenhagen and has contributed to a deeper understanding of our metabolism by studying the cross-talk of our central nervous system and our metabolism (stress and rest in humans). She’s an expert in cold & heat therapy and functional breathing for optimized health and performance. She is the founder of the “Soeberg Institute”. She communicates and teaches her knowledge via her online programs, books, SoMe, podcasts, talks and workshops.

One of her principles is to “end cold” to increase metabolism and prolong the benefits of chemicals in the brain. A principle, that Professor Andrew Huberman from Stanford University named after her: The #soebergprinciple.

Supporting studies

  • Altered brown fat thermoregulation and enhanced cold-induced thermogenesis in young, healthy, winter-swimming men • PMID: 34755128

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