Most replayed moment: Ice Baths: Science or Fad? | Susanna Søberg & Prof Tim Spector

Summary

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Podcast Summary:

ZOE Science & Nutrition
Episode: Most replayed moment: Ice Baths: Science or Fad? | Susanna Søberg & Prof Tim Spector
Host: Jonathan Wolf
Date: May 19, 2026

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Episode Overview

This episode dives deep into the science behind cold water therapy — including ice baths, cold showers, and winter swimming. With their recent surge in popularity, these cold exposure practices promise numerous health benefits, but are they truly backed by science? Host Jonathan Wolf is joined by Dr. Susanna Søberg (a renowned researcher on cold exposure) and Professor Tim Spector (ZOE co-founder and gut health expert) to break down the latest evidence, debunk myths, and share actionable advice for integrating cold exposure into daily life.

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Key Discussion Points & Insights

1. What Happens to Your Body in Cold Water?

[00:59] Dr. Susanna Søberg:

• Immersing in cold water is a potent whole-body stressor, far more so than a cold shower.
• Cold exposure instantly activates skin cold receptors and sends danger signals to the brain.
• The body shifts into survival mode, releasing noradrenaline and activating brown fat, a process distinct from daily temperature regulation.

"So immersing yourself into cold water will mean that you will put this very, very big stressor on your body... the potent of activating your cold receptors in the skin is like 100%. ...sending a rapid signal to your brain that now you are definitely in a situation where you are in danger, actually."
— Dr. Susanna Søberg [00:59]

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2. The Science of Brown Fat

[02:00] Dr. Søberg:

• Humans have two main types of fat: white (energy storage, often unwanted) and brown (energy burning, beneficial).
• Brown fat increases metabolism and can "burn" white fat, improving insulin sensitivity.
• Brown fat is full of mitochondria, similar to muscle tissue; having more brown fat correlates with better metabolic health.
• A landmark 2014 study showed simply sleeping in a cool room (19°C for a month) increased brown fat activity and improved insulin sensitivity in humans.

"The more we have of brown fat cells, the more mitochondria we have, the better insulin sensitivity we have. And also it can burn more fat in our body, not only when we are activating it on purpose, but also when we are just like sitting here."
— Dr. Susanna Søberg [03:20]

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3. Actionable Advice: How to Start with Cold Exposure

[05:00] Dr. Søberg:

• Anyone can try cold exposure—don't overthink it or make it competitive.
• Begin with 30-second cold showers or brief cold plunges; use nasal breathing to stay calm and avoid hyperventilating.
• Never dunk your head (head "donking"); it has no extra benefit and increases fainting risk.
• Goal: Get past the initial cold shock (~30 seconds to 1.5 minutes for beginners). Adaptation varies by individual.
• Progress gently and don't compare yourself to others.

"Cold exposure is an inner journey... A cold plunge is definitely a good place to go if you have that, the ocean... if you don't, then a cold shower is also fine to get started. So 30 seconds cold shower. Use your nose to calm your nervous system."
— Dr. Susanna Søberg [05:24]

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4. Saunas & Combining Hot and Cold

[08:01] Dr. Søberg:

• Saunas are beneficial in combination with cold plunges due to the cardiovascular "workout" from temperature extremes.
• You do not need to combine sauna and cold for health benefits—doing one or the other still works, though alternating is more intense for your blood vessels and cells.

"The thing about alternating between one extreme temperature and the other... is that you push your cardiovascular system and that is a workout for all your blood vessels."
— Dr. Susanna Søberg [08:27]

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5. Cryotherapy vs. Cold Water Immersion

[09:08] Prof. Tim Spector & Dr. Søberg:

• Cryotherapy (short sessions in very cold air) also activates cold receptors and brown fat, and can benefit metabolism.
• However, cold water immersion is more potent: it surrounds the body completely, combines cold with hydrostatic pressure, and elicits a stronger stress response ("cold shock").
• Cryotherapy is effective as a convenient option, but immersion produces stronger effects.

"When you submerge into cold water, you also have that hydrostatic pressure from the water... So that's, of course, more potent to activate your metabolism and also all your chemistry in the brain."
— Dr. Susanna Søberg [10:36]

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6. Do Cold Showers Work?

[11:17] Dr. Søberg:

• Cold showers are beneficial and activate cold receptors, brown fat, and neurotransmitters (noradrenaline, dopamine).
• Evidence (Dutch study) shows 30-second cold shower finishes reduce sick days—possibly through increased energy, not just immunity.
• Cold showers are less "full" than immersion, but still worthwhile.

"There's a study... showing that if you... end your showers on 30 seconds cold showers, you will have less sick days at work... it will activate your... brown fat. It will also activate noradrenaline and dopamine, and you will get that increase in your sympathetic nervous system."
— Dr. Susanna Søberg [11:17]

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Notable Moments & Quotes

• "Cold exposure is an inner journey."
  — Dr. Susanna Søberg [05:24]
• "Try to get over the cold shock. That is the goal."
  — Dr. Susanna Søberg [07:15]
• "It's not because the body needs to feel like it's dying in order for you to get the benefits."
  — Dr. Susanna Søberg [10:36]

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Timestamps for Important Segments

• 00:59 — What happens in the body during cold exposure
• 02:04 — Brown fat explained; why it matters
• 03:00-04:30 — Scientific studies on cold exposure and health (insulin sensitivity, metabolism)
• 05:00 — Practical starting tips for cold exposure
• 07:15 — How to progress past the initial cold shock; adaptation varies
• 08:01 — Benefits of combining sauna and cold, and whether it's required
• 09:08 — Cryotherapy vs. cold water immersion: similarities & differences
• 11:17 — Do cold showers work? Benefits and practical implications

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Summary & Takeaways

• Cold exposure (especially full-body water immersion) offers real, scientifically-supported benefits, notably by boosting brown fat, metabolism, and possibly insulin sensitivity.
• Start slow with cold showers or brief plunges; nasal breathing helps regulate the stress response.
• Saunas and cold exposure are each independently beneficial, but alternating gives an added cardiovascular workout.
• Cryotherapy can substitute for convenience but is less potent than water immersion.
• Even 30-second cold showers provide meaningful stimulation and energy boosts.
• Approach cold exposure as an "inner journey"—progress at your own pace, with safety and self-compassion.

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Transcript

[A]

Hello and welcome to Zoe Recap, where each week we find the best bits from one of our podcast episodes to help you improve your health. Today we're diving into one of the most requested topics we've ever had. Cold water therapy, cold showers, ice baths and wild winter swimming have exploded in popularity over recent years, with supporters claiming a range of health benefits. But are these claims actually backed by science or is it all just another wellness fad? I'm joined by Dr. Susannah Soberg and Professor Tim Spector to break down the studies and discover if we could all do with a bit more ice in our life. The cold plunge. What happens when, like, I'm thinking about my own personal experience of like going into the sea in England, which I've done once, cause it was way too cold. It's very unpleasant. What's going on in your body as you do that?

[B]

Yeah, a lot of things are going on in your body when you go into the cold water. It's very different from a cold shower also. But we can get back to that. So immersing yourself into cold water will mean that you will put this very, very big stressor on your body because the body is in a natural temperature. You don't want to get too cold. But this is so potent because it surrounds your body immediately when you. With no air, of course. So the potent of activating your code receptors in the skin is like 100%. And that is like a huge stressor, sending a rapid signal to your brain that now you are definitely in a situation where you are in danger, actually. So the body acts as if you are in danger, even though you do it deliberately and sends a signal to the brain to regulate your body so that you can better survive this. So it sends out noradrenaline to activate your brown fat.

[A]

And Susanna, can you explain exactly what is brown fat?

[B]

We have two kind of fat tissues also in the body and one of them is the white fat, which we know. It's on our belly, it's on our thighs and we want to get rid of that because it can grow and it's so difficult to activate it and get rid of those fat pearls, you can say, because it's all fat pearls just stuck together. So that stores our energy in the body. Quite opposite to that, we have the brown fat. The brown fat actually increases our metabolism, so the brown fat can burn the white fat. So it's kind of like a good fat. And we could say that the white fat is a bad fat, but we also need some of that white fat. But the brown fat we want to increase so that we can have a higher metabolism. Metabolism or energy expenditure, both when we are purposely activating it, but also when we are just sitting here or when we are asleep. The more we have of the brown fat, the better. It's just like you can compare it to the muscles. So we all agree and know today that it's good to have a lot of muscle mass because there's a lot of mitochondria in the. In the muscle fibers. And the more we have of those, the better its functioning and it increase our insulin sensitivity. And it's the same with the brown fat cells. The more we have of brown fat cells, the more mitochondria we have, the better insulin sensitivity we have. And also it can burn more fat in our body, not only when we are activating it on purpose, but also when we are just like sitting here. So our basic metabolic rate will actually go up if we have more brown fat. Brown fat has been one of these research areas for hundreds of years that we have known about. But it was not until actually the millennium that we discovered that a little bit of cold exposure could actually change our metabolism. So our glucose balance and our insulin sensitivity in humans. And this is so fascinating. It's a study from 2014 showing where the researchers had people who had a bad insulin sensitivity and some of them were obese and some of them had type 2 diabetes. And they had them sleep in a room was 24 degrees Celsius for a month and then they measured their brown fat. Then they slept at 19 degrees for a month and then again measured their brown fat and also insulin sensitivity. And what they found was that sleeping in a room at night at 19 degrees Celsius actually increased their insulin sensitivity and the glucose clearance got better. And when you then looked at the measure of the brown fat, you can see that it had increased. And that was just from sleeping at 19 degrees in a cold room for a month.

[A]

Susanna, I'd love to switch to actionable advice now. So if someone's listening to this, they've never done it before. They didn't grow up in Scandinavia, so they weren't wild swimming and, you know, jumping into a sauna the other time. How can they integrate this into their lives? And I'm also very interested in, like, how can they start if they might be a cold sissy like me?

[B]

Yeah. So if you are cold sissy like you or me, I think the best thing you can do is don't think too much about it. Actually, if you want to Try it out, then go and try it out. But don't have expectations like I have to sit there for a while. This is not a competition. Cold exposure is an inner journey. So you use some kind of cold exposure. I would say a cold plunge is definitely a good place to go if you have that, the ocean, if you have that or if you don't, then a cold shower is also fine to get started. So 30 seconds cold shower. Use your nose to calm your nervous system. So breathe in through your nose and out through your mouth if you need to. And if you can switch totally to nasal breathing, that will help your nervous system to calm down as well. And you can use that also with cold plunging. So breathe in through the nose to calm the nervous system and never do any hyperventilating breath work before or during your cold plunges. That is also, I think, a important to note. And head donking, please don't do that because that would just decrease the blood flow to the brain and it actually also increases the risk of fainting and we also don't want that. And you have no extra benefits of putting your head down in the water. You can splash some water to the face, which will activate the vagus nerve. But dunking your forehead down doesn't do any health benefits for you. So take it slow and feel what is good for you. But breathe through 10 seconds and that is fine. But try to get over the cold shock. That is the goal.

[C]

So try and get past the first 30 seconds.

[B]

Yeah, I think the cold shock is. It might actually be a little bit longer than that. For new people it could be up to one minute and for some, one and a half depending on how cold adapted you actually are in the first place. So back to the question that Jonathan asked. So how different is this from people to people? And it can be actually very different. So if you are used to being much outside, for example, then you get very quickly adapted. But if you are not very much outside, an outdoors person, then you would take a little bit longer to get adapted to the cold. So be gentle to yourself and don't compare yourself to others.

[C]

And I like to have a sauna first, but does it make much difference?

[B]

Do you think you can tim start with the sauna? And I mean, people should do it the way that they feel is best for them. But if you start in the cold water, you will have that increase in oxytocin, noradrenaline, dopamine will change how you sit in the sauna because it's sort of like a place where you meditate.

[A]

Also, in order to get the health benefits, do I need to combine a cold plunge and a hot sauna together?

[B]

No, you don't have to combine them. The thing about alternating between one extreme temperature and the other, like this cold plunge and the sauna, is that you push your cardiovascular system and that is a workout for all your blood vessels. That is one thing. But also going from one extreme to the other will push your cells to either activate to generate heat or to shut down. And that is also a workout for your body. So in that sense it's, it has benefits doing it together. But if you just do cold plunges on one day and saunas on other days, that is also getting the benefits. It's just more like divided, you can say.

[C]

Susanna, can I ask. Our US listeners will know all about cryotherapy. And I was in Los Angeles recently and every shopping mall has a cryotherapy center now. So you can just pop in and do your 3 minute cryotherapy session and go back to work. So it's incredibly practical. You don't have to find a lake in the middle of a city and shiver and. Yeah, and it's reversed because you go in and the first 30 seconds are quite fun. And then it gets progressively colder because it's minus 100 degrees in this freezer and you come out after three minutes. It's. The last 30 seconds are tough. But I got a similar buzz after it. But I wondered, is there any science behind the difference? Is it as impressive as the cold water stuff?

[B]

So there are studies showing that the cryotherapy also activates your cold receptors, which means it also activates the brown fat. And I think that it's the three minutes with these extreme temperatures, it would definitely help on your metabolism. But of course there are differences because when you submerge into cold water, you also have that hydrostatic pressure from the water, which.

[C]

Yeah, and I didn't feel I was going to die either. That was the other thing. So I didn't get the gasping or the sort of life threatening feel of it.

[B]

It's not because the body needs to feel like it's dying in order for you to get the benefits. You do get some benefits. And I do think that the cryo actually has benefits. It's just another modality, it's just another dose that you get. But you can say when you submerge into cold water that is surrounding yourself with like the 100% molecules around your body in cold, you cannot be packed more into cold. So that's of course more potent to activate your metabolism and of course also all your chemistry in the brain.

[A]

So we had another common question around this, actually, which is, does a cold shower work at all or does it need to be like a full plunge into icy water?

[B]

So cold showers work because you do get cold, of course, and you activate your cold receptors. There's a study, a randomized control study from the Netherlands, showing that if you do that for 30 seconds cold, end your showers on 30 seconds cold showers, you will have less sick days at work. It might be that it's not because you actually get less sick. It might actually be that you just get more energy to go to work. I'm not sure about what exactly is going on there, but it's definitely not a bad thing that you feel fresh enough to go to work. So it will activate your CO receptors, your brown fat. It will also activate noradrenaline and dopamine, and you will get that increase in your sympathetic nervous system, but it's probably not going to activate your parasympathetic part of your nervous system. And that is kind of what I would like people to experience, that they have this kind of stress up and also the stress down.

[A]

As you can imagine hosting this podcast, running Zoe, juggling family life, it all keeps me pretty busy. So I try as best I can to stay energized and show up well in all those parts of my life by fueling my body with the right food, by exercising, and by adding a scoop of daily 30 to my meals every day. If you haven't heard of Daily 30 yet, it's the gut supplement designed by our gut health scientists here at Zoe. It's made of over 30 high quality hand picked plants, including seaweed, fungi and different types of fiber. Better yet, it contains ingredients that support gut health, digestion and energy, which is ideal for packed calendars and busy lives. Simply add one scoop a day to any meal for an extra boost of fiber and plant diversity. And because it tastes delicious on just about anything and adds a satisfying crunch, it quite quickly slots into your life, becoming a daily healthy habit you'll always have time for. By the way, whenever we talk about Daily 30 as a good source of fiber, we're required to say that it contains 4 grams of total fat per serving. Obviously, that's all amazing healthy fats from plants. So order yours [e-mail] daily30. Thanks for listening and see you next time.

[B]

Sam.