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Most of us avoid the cold. We crank up the heating, bundle up in layers, and curse every icy gust of wind. But what if freezing — or even sweating — could be the key to better health?

In this episode, Jonathan is joined by two world-leading scientists to explore a radical idea: that extreme temperatures might unlock powerful benefits for your metabolism, mental health, and even longevity.

Dr. Susanna Søberg, the researcher who coined the “Søberg Principle,” has spent years studying the effects of cold plunges and saunas on the human body. Her findings? Just minutes of exposure a few times a week could improve insulin sensitivity, activate brown fat, and lower stress.

She’s joined by Prof. Tim Spector - professor of genetic epidemiology at King’s College London, one of the world’s top 100 most cited scientists, and scientific co-founder at ZOE - who explains how these temperature shocks may even impact your gut microbiome.

This episode will change how you think about discomfort, explain the science behind extreme temperatures and might just inspire your healthiest new habit.

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00:00 Can saunas improve metabolism?

02:03 Can heat really mimic a cardio workout?

05:13 Why do I feel sleepy after a sauna?

07:33 The surprising link between heat and your heart

10:37 What cold water instantly triggers in your body

13:19 This 'good fat' burns your bad fat — here’s how

16:11 How just walking in the cold can raise your metabolism

18:57 Why a colder bedroom could transform your blood sugar

22:07 Winter swimmers vs non-swimmers — the science is clear

25:39 How short dips beat long soaks in cold water

29:12 Cold plunges activate your cell repair systems

31:37 The 30-second switch: from panic to peace

33:58 Can cold water really boost mental health?

36:07 Could gut bacteria respond to temperature?

38:53 Cold plunges and antidepressants: early findings

41:01 Cold shock vs hyperventilation — what to avoid

43:27 Is combining hot and cold better than just one?

45:36 Cryotherapy vs cold plunge — which works better?

47:19 Do cold showers actually do anything?

50:59 Why daily plunging might be too much stress

53:31 Should women cold plunge differently than men?

📚Books by our ZOE Scientists

The Food For Life Cookbook

Every Body Should Know This by Dr Federica Amati

Food For Life by Prof. Tim Spector

Mentioned in today's episode:

Altered brown fat thermoregulation and enhanced cold-induced thermogenesis in young, healthy, winter-swimming men, Cell (2021) 

Cold exposure, gut microbiota and health implications: A narrative review, Sci Total Environ (2024) 

The gut microbiota facilitate their host tolerance to extreme temperature, BCM Microbiology (2024) 

Have feedback or a topic you'd like us to cover? Let us know here.

Episode transcripts are available here.