Not because I want to impress you with numbers. But because I think you deserve to understand what you are part of when you follow this work — and what is being built for the future.

Where it started

The Thermalist® Method began as a research question. What does structured thermal exposure — the deliberate alternation of cold and heat — actually do to the human body? And can we be specific enough about the answer to turn it into a teachable, repeatable, measurable practice?

The peer-reviewed answer — the Søberg Principle, published in Cell Reports Medicine in 2021 — confirmed that yes, we could. Structure determines outcome. The sequence matters. The physiology is specific.

From that foundation, the method has grown into something I could not have fully imagined when I was collecting data in Copenhagen.

What exists today

Four online courses at the Søberg Institute — covering everything from a first introduction to the method through to a full 12-week personal metabolic protocol. Thousands of students across more than 127 countries. A 5-star rated course catalogue built entirely on the published science.

A global newsletter — 25,000 subscribers across 127 countries, reaching the United States, United Kingdom, Australia, Canada, Denmark, and beyond. A community of people who have chosen to follow the science rather than the trend.

More than 250 certified Thermalist® instructors in more than 25 countries — practitioners who have been trained directly in the method and are delivering it in wellness facilities, health clinics, fitness studios, and spa environments worldwide.

And now — the Thermalist® Recovery System. The next evolution of the method. A complete contrast therapy operating system for premium wellness facilities, spa hotels, and hospitality operators — incorporating structured programming, staff certification, guided sound experiences, and a member-facing technology ecosystem. Built on the same published science. Designed for real commercial environments.

Why I am telling you this

Because I want you to understand something important about what the Thermalist® Method is — and what it is not.

It is not a wellness brand that commissioned research to support its marketing. The research came first. The Søberg Principle is published. The science is real. Everything built on top of it is a translation of that science into the real world.

That matters — not just for credibility, but for what it means about the future. A method built on genuine science does not expire when the trend moves on. It deepens as the research develops. It strengthens as more practitioners apply it and more data is gathered.

The Thermalist® Method is fifteen years of research in the making. It will be here in fifteen more.

What is coming

The Thermalist® Recovery System is now launching to selected founding partners in premium wellness and hospitality. The app ecosystem that supports it is in development. The science behind it continues to develop.

And the Søberg Institute will continue to publish — new research, new courses, new tools — for the individuals and practitioners who want to go deeper.

You are part of that community. And I am grateful for it.

If you are a wellness operator or know one who should be part of the Thermalist® Recovery System founding partner programme — the application is open at thermalist.com.

→ Thermalist® Recovery System — thermalist.com

→ All courses — soeberginstitute.com

Thank you for reading. Thank you for supporting this work. 🌊

— Dr. Susanna Søberg

The landmark Finnish longevity studies. The cardiovascular research. The athletic recovery literature. The majority of participants were men. And while the findings are valuable — and many of the benefits translate across sexes — the specific ways in which sauna therapy interacts with female physiology have been largely overlooked.

As a female metabolic scientist who has specifically studied the differences between male and female responses to thermal exposure, I want to address this gap directly.

Because women are not simply smaller men. And the dose, the timing, and the protocol that produces optimal outcomes for a man is frequently not the right approach for a woman.

What we know — the established science

The heat shock protein response to sauna exposure applies equally to women and men. HSPs play a critical role in cellular repair, protein folding, and protection against the cellular damage associated with aging. For women — who face specific challenges around inflammation, hormonal transitions, and oxidative stress — this cellular repair mechanism is particularly relevant.

The cardiovascular benefits of regular sauna use are also well established and applicable to women — and arguably more important. After menopause, when oestrogen’s protective cardiovascular effects diminish, the cardiovascular training stimulus of regular thermal exposure becomes one of the most accessible and evidence-supported tools for maintaining cardiovascular health.

The nervous system effects are where I find the most compelling case for women specifically. Women are disproportionately affected by chronic stress — not because of psychology, but because of biology. The interaction between cortisol, oestrogen, and progesterone creates a more complex stress response than in men. Regular structured sauna practice — particularly in combination with cold exposure, as in the Thermalist® Method — trains the autonomic nervous system in ways that are directly relevant to female stress physiology.

What women need to know that most sauna content ignores

The menstrual cycle influences thermoregulation. In the luteal phase — the second half of the cycle after ovulation — progesterone elevates basal body temperature and the physiological cost of heat exposure is marginally higher. Paying attention to how your body responds during different cycle phases and adjusting intensity accordingly is part of an intelligent practice.

During perimenopause and menopause — when thermoregulation becomes less stable and hot flashes are common — there is emerging evidence that regular thermal training may support thermoregulatory adaptation over time. This is an area where the research is still developing, but the biological mechanism is plausible and the anecdotal evidence from women in the Thermalist® community is consistent.

And pregnancy: sauna use during pregnancy is generally not recommended, particularly in the first trimester and at high temperatures. Always consult your physician.

My personal view

I believe the science of thermal health for women is one of the most underdeveloped areas in the wellness research landscape. Most of what I have built — the Thermalist® Method, the Søberg Principle, the contrast therapy system — was developed with both male and female physiology in mind, because the research demanded it.

Women deserve precision in this space. Not generic wellness content adapted from male research. Actual science that takes female physiology seriously.

That is what I am building — and what I teach in the courses at the Søberg Institute.

→ The 3 Week Thermalist Cure® — soeberginstitute.com

→ Søberg® 12-Week Reset — soeberginstitute.com

Share this with a woman in your life who deserves the honest science. 🌊

— Dr. Susanna Søberg

Share The Thermalist® Journal

Cold and heat are everywhere right now. A billion views, endless videos, a new claim every week. I want to say plainly where I stand, because I have always tried to tell you both halves of the truth at once.

There is a real core here. The mechanisms are established. Cold sets off a clear stress response in the body. Cold and heat measurably change how we handle energy over time. Part of that work came out of my own research, published in Cell Reports Medicine, including the weekly protocol you may have heard me talk about, eleven minutes of cold and fifty seven minutes of heat. That core is solid. I stand on it every day, and I am proud of it.

What I cannot tell you honestly is that the enormous tower of claims built on top of that core has been proven. Claims about hormones, immunity, fat loss, longevity. Most of it has barely been tested in real people, and some of it not at all. The confidence around these claims is enormous. The evidence under most of them is thin.

This matters because of a difference almost nobody talks about. Reading a study is not the same as proving something. A great many people now call themselves science backed because they have read a paper or two. Having read the literature and understanding where that literature stops are two very different things, and the second one takes years. The certainty you see online is mostly borrowed from abstracts, not earned from the whole picture.

We have been here before, and that is the part that should give us all pause. A little over a century ago there was an enormous movement built on cold and water. Hundreds of clinics across Europe and America. Huge belief. Then it almost entirely vanished, because when the moment came to prove itself, it could not, and it had promised far too much. The strand that survived was the one that worked with the science and wanted to be tested.

So here is what I am going to do. I am going to spend this next chapter holding what we genuinely know apart from what we only assume, and then going and measuring the difference, properly, in real people, over real time. That is the only honest way forward, and it is the work I care about most.

I would love your help shaping it. So before you close this, tell me one thing. What question about cold, heat, or contrast therapy would you most like to see answered with real research? Reply in comments below. I read them.

More soon,

Susanna

We know more about nutrition than any generation in history. More about exercise. More about sleep, about disease, about the machinery of aging itself. The knowledge that a few decades ago lived only in journals and the heads of specialists now sits in everyone’s pocket. And in the last few years something stranger has happened on top of all that. We built machines that can answer almost any health question we can think to ask, instantly, patiently, and often better than the human we would otherwise have asked.

By every reasonable measure, the information problem in health is being solved.

And yet walk through any city and you will not find a population that feels well. People are tired in a way sleep does not fix. Anxious in a way no protocol resolves. Surrounded by more guidance than anyone could follow and somehow less certain than ever about what to actually do. We have answered the question and not solved the problem, which usually means we were asking the wrong question.

I think we were. I think we have spent a century operating on an assumption so basic that almost no one has examined it. The assumption is that more information produces better health. And I think the age of AI is about to prove, decisively, that it never did.

Knowledge is going to zero

Start with what is actually happening to information, because the economics of it matter more than the content.

For most of history, health knowledge was scarce and therefore valuable. It was locked behind training, behind access, behind the slow work of finding the right person to ask. If you knew something true about nutrition or recovery that most people did not, you held an advantage, and the advantage was real precisely because the knowledge was hard to get.

That world is ending quickly. Health knowledge is being democratized at a speed that is genuinely difficult to absorb. A machine can now explain nutrition, training, metabolism, fasting, cold exposure, supplementation, and disease prevention to you, at any hour, tuned to your exact question, with more breadth than almost any individual expert alive. It does not get tired. It does not gatekeep. It costs almost nothing.

This is, on its own, a wonderful thing. I am not mourning it. But it has a consequence that very few people in the health world have sat with honestly.

When something becomes abundant, it stops being the advantage.

This is one of the oldest laws there is. Value does not live in what is plentiful. It lives in what is scarce. When a resource that was once rare becomes free and universal, the advantage does not disappear. It migrates. It moves to whatever is still scarce, to the next bottleneck in the chain.

So the real question is not how good the information is getting. The information is getting extraordinary. The real question is the one almost no one is asking. When everyone has access to the same perfect knowledge, what becomes scarce?

Where the capacity actually gets built

Everything in this essay points to a single, slightly inconvenient conclusion. The knowing is now free. The becoming is not, because the becoming happens in the body, through structured practice, over time.

That is what my courses at the Søberg Institute are for. Not to sell you information that an algorithm will hand you for nothing, but to give you the tested structure to turn it into a capacity you actually own. Each one is built on the Søberg Principle and over fifteen years of research, and each one is, in its own way, a method for building back a piece of the adaptability modern life quietly removes.

Thermalist® Method at Home. A 3.5-hour self-paced introduction to the full method. The clearest place to start if you want to understand how cold and heat train the body, and how to practice them correctly rather than enthusiastically.

Cold Water Immersion Course. The full science of cold, with comprehensive safety guidance. For building genuine cold adaptation, the kind that lives in the body and cannot be downloaded, on a foundation that keeps you safe while you do it.

The 3 Week Thermalist Cure®. A structured three-week programme combining cold, heat, and breath. A deliberate, time-bound reintroduction of the challenge and recovery the body adapts to.

The Søberg® 12-Week Reset. A guided twelve-week metabolic protocol. The longer arc, for rebuilding metabolic flexibility and recovery capacity as a lasting part of how your body works.

The information about all of this is, in a sense, already free. What these give you is the structure to build the thing the information was always pointing at and could never deliver on its own.

Read more

For most of human history, healthcare has been a story told backwards.

Something broke. You felt it. Then you went looking for help, often too late, and medicine did what it could with what was left. The doctor was a historian of the body, reading the damage after the fact. We called this care, and for thousands of years it was the only kind we had.

We are now leaving that world. For the first time, disease may increasingly be seen before it is felt. The signal is arriving ahead of the symptom.

This is the part everyone talks about, so I will move through it quickly. Wearables read your heart rate, your sleep, the variability between each beat. Continuous monitors turn a single meal into a curve. Blood biomarkers, once measured every few years, are starting to be tracked across months. Algorithms trained on millions of people can flag the faint statistical shadow of a disease years before it would announce itself. The body, for the first time, is becoming legible in advance.

I work in metabolic science, and I do not want to be the person who stands in front of this and frowns. Some of it is genuinely extraordinary. Catching a cancer at stage one instead of stage three is not a lifestyle upgrade. It is a life.

I am interested in a quieter question, one almost no one is asking while we are busy being amazed. What does it do to a human being to live inside a system that watches their body more closely than they ever could, and increasingly decides for them what their body needs?

Read more

They track their glucose in real time. They weigh their protein. They can recite their body fat percentage from memory, and there is a spreadsheet behind their supplement stack. By every metric we have agreed to care about, they are doing well.

Then a flight gets delayed, they miss a meal, they sleep four hours in a strange hotel, and the whole system collapses. Irritable. Foggy. Ravenous. Useless. One disruption, and the machine stalls.

We would not call a car reliable if it only ran on a perfectly flat road at exactly 21 degrees, with premium fuel and no passengers. We would call it fragile. Yet this is precisely the condition we have learned to call healthy, and we spend enormous effort trying to manufacture the flat road rather than asking why we can no longer handle a hill.

I have spent my career studying metabolism, brown fat, and how the body responds to cold and heat. The longer I do this work, the more convinced I become that we have been measuring the wrong thing entirely.

The question we never ask

Almost everything sold under the banner of metabolic health is a question about level. How many calories. How low the body fat. How flat the glucose curve. How much protein. How efficient the burn.

These are all questions about a single point on a graph. They describe a snapshot of the body under one set of conditions, usually favorable ones.

The question I almost never hear anyone ask is about range. Not how your metabolism performs when everything is perfect, but how wide a band of conditions it can absorb before something gives. Not the height of the peak, but the width of the floor you can stand on.

A resilient metabolism is not the one that burns the most calories. It is not the one with the lowest body fat. It is not even the one with the flattest blood sugar. A resilient metabolism is the one that can move between states. Fed and fasted. Hot and cold. Stressed and recovered. Awake and asleep. It moves between all of them without falling apart.

Read more

I want to cut through the noise and give you the clear, honest scientific picture — because contrast therapy, when you understand what it actually is and how it actually works, is one of the most powerful physiological tools available to us.

And I say that not as someone who discovered it on social media. I say it as a scientist who has spent over 15 years studying exactly what it does to the human body.

The simple definition

Contrast therapy is the deliberate, structured alternation between cold exposure and heat exposure — for specific physiological effect.

The word structured is the key one. Contrast therapy is not simply getting cold and then warm. It is the application of thermal stress in a specific sequence, at specific intensities — with the structure of that sequence directly influencing the physiological outcome.

This is the central insight of the Søberg Principle — my peer-reviewed research published in Cell Reports Medicine in 2021. How you structure a contrast therapy session determines what your body does in response to it.

What the science actually shows

Cold exposure triggers brown fat activation, a significant norepinephrine surge, cardiovascular training, and immune system activation. Heat exposure activates heat shock proteins for cellular repair, produces cardiovascular conditioning, and supports nervous system recovery.

The deliberate alternation of these two states — done in a structured sequence — creates a combined effect greater than either cold or heat alone. It is a comprehensive training stimulus for the body’s regulatory systems simultaneously.

This is why I built the Thermalist® Method as a system — not as a single tip or a single protocol. The science of contrast therapy is too specific, too nuanced, and too individual to be reduced to a social media post.

The ancient practice validated by modern science

It is worth noting that contrast therapy is not new. Roman bathhouses alternated between hot and cold pools. Scandinavian sauna culture has included cold lake plunging for centuries. The traditional Finnish sauna practice almost always concludes with cold exposure.

What is new is the precision. We can now measure exactly what happens in the body during and after structured contrast therapy — and that precision is what makes it possible to practice it intelligently rather than simply enthusiastically.

— — —

I cover the complete science of contrast therapy — including the Søberg Principle, brown fat activation, the nervous system effects, safety guidance, and how to build an effective practice — in the Thermalist® Method at Home course and the Cold Water Immersion Course at soeberginstitute.com.

→ Thermalist® Method at Home — soeberginstitute.com

→ Cold Water Immersion Course — soeberginstitute.com

The full science journal article on contrast therapy is also available on the Søberg Institute website for those who want the deeper read.

— Dr. Susanna Søberg

Should I be cold plunging? Is it safe during my period? Am I doing it right?

The honest answer is that we don’t yet have a complete picture. What we do know should be changing the way women approach cold and heat exposure entirely.

Should women cold plunge?

Yes. Catecholamine release, brown fat activation, reduced inflammation, improved mood. The physiological case is well established across both sexes.

But how your body responds to cold changes depending on where you are in your cycle. Women vasoconstrict faster than men during immersion, and core temperature drops more steeply. Especially in the luteal phase when progesterone is elevated. The same session that supports recovery in week one can push your stress response in the wrong direction in week three.

This doesn’t mean don’t plunge. It means the protocol should shift with your cycle.

A 2024 study of over 1,100 women who cold water swam regularly found nearly half reported meaningful reductions in anxiety, irritability, and mood swings. Women in perimenopause reported fewer hot flushes and significantly better mood. The practice works. The gap is in the precision.

Should women sauna differently?

Yes, same logic applies. In the luteal phase, progesterone already elevates your core temperature. Research points toward shorter sessions of 10 to 15 minutes in this phase to avoid compounding that thermal load, while still getting the cortisol and mood benefits that regular heat exposure delivers over time.

Does stress hit women and men differently?

Physiologically, yes. Cold exposure that lowers cortisol in a man can raise it in a woman at the wrong point in her cycle. This is one of the most consistent findings in the literature — and one of the most ignored in protocol design.

What we don’t yet know

Most cold and heat studies were done on men. Female-specific data on optimal temperature, duration, fertility effects, and interaction with hormonal contraception is still limited. These are open questions — and important ones.

Next week: Can PMS symptoms be meaningfully reduced with cold and heat?

— Susanna

Want to go deeper? Here's where to start:

The Cold Water Immersion Course Everything you need to start cold water immersion safely — the science, the physiology, and the practical guidance to build it into your life. Evidence-based and self-paced, taught by Dr. Susanna Søberg, PhD.

Thermalist® Method at Home A 3.5-hour online course covering cold exposure, sauna therapy, and breathwork — the science behind why contrast therapy works and how to apply it at home. Built on the Søberg Principle and the Thermalist® Method.

3 Weeks Thermalist Cure® A structured three-week protocol combining cold, heat, and breathwork — practised together to reset your stress response and rebuild resilience. The transformation happens when all three work in sequence, not in isolation.

The Søberg® 12-Week Reset A guided 12-week journey to understand your body, regulate stress, and build sustainable habits across cold exposure, heat, sleep, movement, breathwork, and nutrition. The most comprehensive program in the Søberg Institute.

The Søberg Institute

It comes up at every keynote I give. It is in my DMs every week. It is the first thing most people want to know when they discover cold water immersion for the first time.

Does it help you lose weight?

And I understand why they ask. The wellness world has made enormous claims about cold plunging and fat loss. Some of it is grounded in real science. A lot of it is not. And the honest scientific answer — the one I spent over 15 years researching — is more interesting than either the hype or the scepticism.

So let me give it to you properly.

What cold water actually does to your metabolism

When you enter cold water, your body does something remarkable. It activates brown adipose tissue — brown fat — a type of metabolically active fat that burns calories to generate heat.

This is not the same fat most people think of when they think about weight loss. Brown fat is different. It contains a high density of mitochondria — the energy-producing structures inside cells. Its job is to burn energy, not store it. And cold exposure is one of the most potent activators of brown fat activity we know of.

My 2021 peer-reviewed research, published in Cell Reports Medicine, confirmed that structured contrast therapy produces measurable brown fat activation and improvements in insulin sensitivity — two of the most important metabolic markers for long-term metabolic health and body composition.

So yes — cold exposure has a real, measurable, scientifically confirmed effect on metabolism.

But here is where I need to be honest with you.

Why cold water is not a weight loss shortcut

Cold water immersion is a metabolic tool. Not a weight loss intervention.

The distinction matters more than it might seem.

A tool produces results when used correctly, consistently, and as part of a broader approach. A shortcut produces results regardless of context — or it does not exist at all.

Cold water immersion is not a shortcut. It does not override poor sleep, chronic stress, sedentary behaviour, or a dysregulated relationship with food. What it does is activate and train the metabolic system over time — improving the body’s ability to regulate energy, manage blood sugar, and build metabolic flexibility.

And the most important word in that sentence is: over time.

The people who see the most significant metabolic results from cold exposure are the people who practice it consistently — not intensely, not perfectly, but consistently — and who understand that the cold is one input into a system, not the whole system.

Read more

Most of the foundational research on thermal therapy cold water immersion, sauna use, contrast therapy, even the basic physiology of thermoregulation, was conducted predominantly on male subjects. This was not malicious. It was the default in research design for decades, justified by the belief that hormonal variation in female subjects created confounding variables that made data harder to interpret. The result is a substantial body of knowledge about how the body responds to thermal stress that is implicitly male, applied universally to a population that is half female.

This matters because estrogen does not just influence reproduction. It is deeply embedded in the systems that govern temperature regulation, cardiovascular response to thermal stress, autonomic nervous system function, sleep architecture, and inflammatory modulation. When you remove estrogen from the equation — or when you extrapolate from male data without accounting for it you lose something essential about how the female body actually works.

For those who want to build a sustained, personalised approach to thermal practice that accounts for the full complexity of female physiology across twelve weeks, the Søberg® 12-Week Reset does exactly that it is not a fixed protocol, it is a guided system for building your own.

The Søberg® 12-Week Reset — soeberginstitute.com

The Søberg® 12-Week Reset

If you are newer to cold and heat exposure and want to start with the foundations first, the Thermalist® Method at Home course covers the core science and practice in a 3.5-hour self-paced format.

Thermalist® Method at Home

The Thermalist® Method at Home course covers the intersection of breathwork and thermal practice for your own journey at home. It is the foundation before anything else.

Thermalist® Method at Home — soeberginstitute.com

The hypothalamus as thermostat

The hypothalamus is the brain region responsible for maintaining core body temperature within its narrow optimal range. It receives continuous input from thermoreceptors across the body and adjusts peripheral blood flow, sweat rate, and metabolic heat production in response. In men, this system operates with relative hormonal stability across weeks and months. In women, it is continuously modulated by the hormonal environment.

Read more

Want the full picture? Everything I describe in this article is explored in depth inside the Søberg® 12-Week Reset

— a guided program to help you find out what works for your body, reduce chronic inflammation, and protect against lifestyle diseases like type 2 diabetes. More on what’s inside at the bottom.

Søberg® 12-Week Reset

People assume that because I study cold and heat, that is all I do for my health. The truth is more layered — and I think more useful for you.

What connects everything I do is one concept: metabolic flexibility. This is your body’s ability to switch efficiently between burning carbohydrates and fat. When you lose it, you get chronic inflammation, dysregulated blood sugar, and over time the lifestyle diseases now at epidemic levels — type 2 diabetes, cardiovascular disease, metabolic syndrome. Building it back is what my work is about.

Here is how I do it in practice.

The forest walk

Every morning I walk my dog through the forest. This is not incidental — it is intentional. Walking in nature measurably lowers cortisol, sharpens mental clarity, and for me it is where I do my best thinking. From a metabolic standpoint, low-intensity movement in a fasted morning state trains the body to burn fat efficiently. That is metabolic flexibility in action, before the day has even started.

I also take the stairs, stand at my desk, and never sit for more than an hour at a stretch. Small choices. Enormous compound effect over years.

Strength training

I lift two to three times a week, and I wish I had started sooner. Muscle mass is one of the strongest predictors of healthy aging we have. It improves insulin sensitivity, protects joints, supports bone density, and preserves the functional independence that determines quality of life as we get older. My sessions focus on compound movements — the kind that reflect how the body actually works. The goal is never aesthetics. It is capacity and longevity.

Zone 2 cardio

Once or twice a week I do sustained moderate-intensity cardio — the pace where you could hold a conversation, but it takes a little effort. This is the most direct way to train metabolic flexibility through structured exercise. At this intensity the body preferentially burns fat, mitochondria multiply, and over time the metabolism learns to switch fuel sources efficiently. This is how you build the engine that resists inflammation and insulin resistance.

Cold and heat

This is where my research meets my daily life. Cold exposure activates brown fat, floods the brain with dopamine and norepinephrine, and trains the nervous system to stay calm under stress. Heat exposure drives cardiovascular adaptations comparable to moderate exercise, activates cellular repair mechanisms, and has been linked in large studies to significantly reduced rates of heart disease and early death.

Together they are among the most powerful tools I know for reducing inflammation and building metabolic resilience. But the benefits are entirely dose-dependent — how long, how often, in what order. Get those variables right and the results are remarkable. Get them wrong and you leave most of the benefit on the table. The exact protocols are what I teach inside the course.

The bottom line

Everything I do comes back to the same principle: deliberate, controlled stress makes the body more resilient. Cold, heat, weights, cardio, a morning walk in the forest — these all tell your body to adapt. A body that adapts well is a metabolically flexible body. And that is a body that resists the diseases that are stealing decades from so many people’s lives.

Start with one thing. Walk outside. Add cold to your shower. Pick something heavy up a few times a week.

And when you are ready to go deeper — that is what the Søberg® 12-Week Reset is for.

Søberg® 12-Week Reset

What you get in the 12-Week Reset

Most people spend years trying other people’s protocols and wondering why they don’t stick. The answer is simple: they were never built for you.

The Søberg® 12-Week Reset guides you — week by week — to find out what actually works for your body. Each week introduces a new physiological focus and a practical theme, so you can observe how your body responds and learn to listen to it rather than override it.

Over 12 weeks you work through every pillar of metabolic health:

• Cold exposure — the science, the Søberg Principle, and how to apply it to your life

• Heat therapy — sauna protocols, sequencing, and what the research actually shows

• Movement — structuring your week for metabolic flexibility, not just fitness

• Sleep — the recovery layer most people underestimate

• Breathwork — regulating your nervous system from the inside out

• Nutrition — fuelling metabolic flexibility without obsessing over food

• Stress and nervous system regulation — understanding the inflammation link and how to break it

By the end you will not need to search for the next trend or quick fix — because you will understand your own body well enough to make the right choices for life.

→ Find out what works for your body here

Dr. Susanna Søberg is a PhD researcher, founder of the Søberg Institute, and creator of the Thermalist® Method. She is the author of Winter Swimming and one of the world’s leading voices on temperature therapy and metabolic health.

The people making that argument are not wrong. But they are working from a fragment of the picture — and the part they are leaving out is where the real science lives.

I want to walk through this properly, because it is one of the most common questions I receive, and most of the answers being given online are either alarmist or dismissive. The actual research is more nuanced, more interesting, and more useful than either extreme.

What the research actually shows

When you train with weights, you create deliberate microscopic damage in your muscle fibres. This is not a side effect of training — it is the mechanism of training. The inflammatory response that follows is your body’s signal to rebuild. Satellite cells migrate to the damaged tissue. Protein synthesis accelerates. The muscle repairs slightly stronger than before. This is skeletal adaptation, and it requires that inflammatory window to function.

Cold water immersion, applied in that same window, does interfere with this process. It causes peripheral vasoconstriction — blood vessels near the skin and muscles tighten.

Blood flow to recently worked muscle decreases. The acute inflammatory response, which the muscle needs to initiate its repair cascade, is partially suppressed. Several well-designed studies confirm that cold plunging immediately after resistance training reduces hypertrophy over eight to twelve weeks compared to passive recovery or active cooldown.

The Loughborough University research published in the Journal of Physiology showed that cold water immersion after resistance training blunted the anabolic signalling pathways — specifically mTOR and satellite cell activation — that drive long-term muscle growth. This is real, reproducible, and worth taking seriously.

What I have not covered yet is the practical logic for different training types — and one specific mechanism that most strength athletes overlook entirely when making decisions about cold timing.

If you want to understand how to apply the science of cold and heat to your own training and recovery, that is exactly what the Søberg® 12-Week Reset was built for — a guided twelve-week programme that takes you through metabolic flexibility, recovery, cold and heat exposure, and nervous system regulation in a structured sequence.

Upgrade to paid to read the rest of this post — and access every Friday deep-dive in the archive.

The Søberg® 12-Week Reset works through exactly this kind of decision-making across twelve weeks — not as a fixed protocol, but as a framework for understanding your own body well enough to build one.

The Søberg® 12-Week Reset — soeberginstitute.com

The Søberg® 12-Week Reset

If you are newer to cold and heat exposure and want to start with the foundations first, the Thermalist® Method at Home course covers the core science and practice in a 3.5-hour self-paced format.

Thermalist® Method at Home

Thermalist® Method at Home — soeberginstitute.com

But here is what those same studies do not say

They do not say cold exposure is harmful to trained athletes. They do not say cold exposure is counterproductive for everyone. And they almost universally involve cold immersion applied immediately after training within minutes of the final set.

Read more

Last week, someone sent me a clip from Rooster starring Steve Carell.

In the scene, they casually talk about cold plunges and brown fat activation.

And I had one of those strange moments where you simultaneously laugh… and realize something important has shifted.

Because not very long ago, brown fat was something almost nobody outside metabolic research talked about.

Now it’s appearing in mainstream entertainment.

Not documentaries.

Not podcasts focused on optimization.

Comedy.

That may sound insignificant, but culturally, it’s a very big deal.

As a scientist who has spent years researching metabolism, cold exposure, and contrast therapy, I immediately recognized what this moment represents:

Cold exposure has officially crossed from fringe wellness behavior into mainstream cultural awareness.

And once science enters culture, behavior follows.

Ten Years Ago, Nobody Talked About Brown Fat

When I first began researching cold exposure and metabolism, the conversation was very different.

Cold water immersion was often associated with:

• extreme athletes,

• niche biohacking communities,

• or people simply doing “crazy Nordic things.”

Brown fat was barely part of public language.

Yet inside research labs, scientists were becoming increasingly interested in something fascinating:

Humans possess metabolically active brown adipose tissue — commonly called brown fat — which can become activated through cold exposure.

Unlike white fat, which primarily stores energy, brown fat helps dissipate energy as heat.

In simple terms:
it is part of the body’s natural temperature regulation and metabolic machinery.

Over the last decade, the research around cold exposure, thermoregulation, metabolism, stress adaptation, dopamine, inflammation, and nervous system resilience has expanded enormously.

But science alone does not change culture.

Culture changes when ideas become socially recognizable.

And that is exactly what is happening now.

The “Mainstream Moment” Matters More Than People Think

People often assume mainstream visibility dilutes science.

Sometimes it does.

But it also signals something important:
the public is becoming metabolically curious.

People are beginning to ask:

• What is brown fat?

• Why are people cold plunging?

• Why does stress exposure sometimes improve resilience?

• Why do people feel mentally different after cold and heat exposure?

These are no longer fringe questions.

They are becoming everyday questions.

And honestly, comedy is often the final stage before mass adoption.

Once a topic becomes parody-able, it usually means society already understands the reference.

Nobody needed to explain the joke.

That means the concept has landed.

But Here’s the Problem

Mainstream attention creates two things at the same time:

1. opportunity,

2. and confusion.

As cold plunging exploded globally, so did misinformation.

Protocols became random.

Studios opened without physiological understanding.

People began treating cold exposure like a competition instead of a biological intervention.

Some made it extreme.

Others made it purely aesthetic.

Very few built systems around:

• nervous system regulation,

• metabolic adaptation,

• progression,

• safety,

• or measurable outcomes.

This is exactly why I began building Thermalist®.

Not as another cold plunge brand.

Not as a wellness trend.

But as a structured, science-based framework for contrast therapy and metabolic resilience.

Thermalist® Was Never Built Around “Cold”

Ironically, one of the biggest misconceptions about my work is that it is “about cold plunging.”

It never was.

Cold is simply one stimulus.

The real focus is adaptation.

At Thermalist®, we work with:

• heat,

• cold,

• breath,

• rhythm,

• stress regulation,

• nervous system recovery,

• and metabolic flexibility.

Because health is not built through comfort alone.

It is built through intelligent adaptation.

That is why the protocols matter.

The sequencing matters.

The timing matters.

The transitions matter.

And increasingly, the data matters.

What began as scientific curiosity is now evolving into something much larger:
a new category of structured recovery and metabolic health experiences.

We Are Watching the Birth of a New Industry

I believe we are still very early.

Most people currently see cold plunges as:

• a product,

• a challenge,

• or a social media trend.

But over time, I believe the market will mature into something much more sophisticated:
science-backed systems for stress adaptation and nervous system regulation.

That is where Thermalist® is heading.

Not toward louder extremes.

Toward measurable, structured, repeatable protocols that can be implemented responsibly across studios, hotels, wellness spaces, athletic environments, and healthcare-adjacent settings.

The future is not simply “cold exposure.”

The future is guided physiological adaptation.

And perhaps that is why seeing brown fat discussed in an HBO comedy made me smile.

Because beneath the humor, something deeper is happening:

Metabolism has entered culture.

And once culture changes, behavior follows.

—

Curious About Cold Exposure — But Want to Understand the Science Properly?

As cold plunges and contrast therapy become increasingly mainstream, one thing becomes more important than ever:

Understanding how to apply these tools intelligently.

Because more is not always better.

Timing matters. Progression matters. Recovery matters. Your metabolism, stress levels, sleep, hormones, and nervous system all influence how your body responds to heat and cold.

That’s exactly why I created these programs.

Build Your Own Metabolic Protocol in 12 Weeks

This is my in-depth educational program designed to help you understand:

• metabolism,

• brown fat activation,

• nervous system regulation,

• contrast therapy,

• circadian rhythm,

• recovery,

• and how to build a personalized protocol based on your own physiology and lifestyle.

The goal is not extremism.

The goal is metabolic intelligence.

The Søberg® 12-Week Reset Course

Thermalist® Get Started — Online 5-Hour Course

If you are completely new to cold and heat exposure, this is the ideal starting point.

In this short online course, I walk you through:

• how to begin safely,

• how to structure your first contrast therapy sessions,

• the most common mistakes people make,

• and the science behind why these practices can profoundly influence stress resilience, mood, and metabolic health.

Because cold exposure should never just become another trend.

It should become an informed practice.

Thermalist® Method at Home

Dr. Susanna Søberg
Metabolic Scientist | Founder of Thermalist®

If you enjoy deep dives into metabolism, stress adaptation, nervous system regulation, and the future of contrast therapy, subscribe to The Thermalist® Journal.

I just returned from a very beautiful and meaningful Thermalist® retreats— our Thermalist® Women’s Retreat in Sweden.

And honestly, I am still processing the experience.

There is something incredibly powerful about bringing women together in nature to slow down, breathe differently, move differently, recover differently, and finally begin listening to their bodies again.

Not through restriction.
Not through pressure.
But through regulation.

Throughout the retreat, we explored women’s health from multiple perspectives — metabolism, stress, nervous system regulation, hormones, recovery, movement, and longevity.

We were incredibly fortunate to have inspiring talks from Kayla Barnes, who shared deep insights into women’s health optimization and what biomarkers and measurements women should actually pay attention to when it comes to long-term health and performance.

We were also joined by our own Thermalist® Instructor and women’s health expert, Mirjam Stein, whose calm, grounded, and deeply knowledgeable approach created some truly meaningful conversations among the group.

But one of the moments that stayed with me the most happened outside.

We were generously gifted a pair of barefoot shoes from Vivobarefoot, and together we went on a long nature walk along the breathtaking and windy Swedish coastline.

What began as a simple walk turned into hours of conversation about feet health, posture, grounding, metabolism, nervous system regulation, movement patterns, and how disconnected many people have become from the surfaces they walk on every single day.

The feet are one of the body’s richest sensory interfaces with the external world.

Every step sends information into the nervous system.

When we restrict movement in the feet, flatten sensation, and disconnect ourselves from natural terrain, we also reduce sensory input that helps regulate balance, posture, stability, and even stress responses.

Walking in barefoot shoes across uneven natural terrain requires presence.

Your nervous system pays attention.

Your posture adjusts.

Your gait changes.

Your breathing changes.

And slowly, your body begins to organize itself differently.

Modern research increasingly supports what many people intuitively feel after spending time outdoors:

Nature regulates us.

Exposure to natural light, uneven terrain, fresh air, natural sounds, and fractal visual patterns found in forests, coastlines, and landscapes helps shift the nervous system toward parasympathetic activity — the state associated with recovery, digestion, hormonal balance, emotional regulation, and metabolic repair.

Studies have shown that even short periods in natural environments can:

• reduce cortisol levels

• improve heart rate variability (HRV)

• lower blood pressure

• improve glucose regulation

• restore cognitive focus

• support immune function

The nervous system does not separate “mental health” from physical physiology.

Everything is connected.

And perhaps this is one of the reasons why so many women at the retreat described feeling calmer, clearer, lighter, and more emotionally regulated after just a few days immersed in this environment.

Not because we “escaped life.”

But because we returned to conditions the human organism still recognizes.

Throughout the retreat, we also guided multiple Thermalist® sauna sessions combined with our sound experience.

And once again, I watched participants enter the sauna carrying tension, overwhelm, and mental noise — only to slowly soften into presence, stillness, and regulation.

These moments affect me deeply every single time.

Because as a scientist, you spend years studying physiology, biomarkers, mechanisms, and nervous system responses on paper.

But witnessing regulation happen in real time — seeing someone’s breath slow, their shoulders drop, their eyes soften, their nervous system shift from survival toward safety — that is something entirely different.

Those honest moments are why I continue this work.

Seeing people reconnect with themselves is what I live for.

This retreat reminded me again that women’s health is not only about hormones, supplements, or optimization.

It is also about environment.

Light.
Nature.
Movement.
Temperature.
Breath.
Connection.
Safety.
Rhythm.
Recovery.

The female nervous system was never designed to live permanently overstimulated, indoors, disconnected from natural cycles and sensory input.

And perhaps part of healing is not adding more complexity — but removing enough noise that the body can finally regulate again.

In clarity and balance,

Dr. Susanna Søberg
PhD in Metabolism | Founder of the Thermalist Method®

soeberginstitute.com

Build Your Own Metabolic Protocol in 12 Weeks

For years, people have asked me one question over and over again:

“How do I actually apply all of this in real life?”

Not just understand metabolism.
Not just listen to another podcast episode.
But truly build a healthier, more resilient body and nervous system in a way that fits their life.

So over the past months, I’ve been quietly building something new.

Today, I’m opening enrollment to:

The Søberg® Reset — A 12-Week Metabolic Protocol

This is not a traditional online course.

It is a guided 12-week journey designed to help you understand your body, regulate stress, improve metabolic flexibility, and build sustainable habits around cold exposure, heat, sleep, movement, breathwork, recovery, and nervous system regulation.

Each week introduces a new physiological focus and a new practical theme.

You will not be overwhelmed with endless information, restrictive routines, or “biohacking overload.”

The Søberg® 12-Week Reset

Instead, you will be guided step-by-step through powerful changes that allow you to observe how your own body responds.

Inside the course, you’ll move through:

• weekly filmed sessions

• practical protocols

• guided reflections

• interactive learning experiences

• weekly focus exercises

• nervous system and energy tracking

And most importantly:

By the end of these 12 weeks, you will have built your own personal protocol.

Not a rigid system copied from someone else.
Not another routine you cannot sustain.

But a protocol that works for you — in your life, with your body, your stress levels, your schedule, and your goals.

You will learn how to read your own biology.

You’ll begin to understand:

• what gives you energy

• what drains you

• how your body responds to stress

• what helps you recover

• and which habits create real and lasting change for you personally

The goal is not perfection.

The goal is empowerment.

So that after these 12 weeks, you no longer need to search endlessly for the next protocol, trend, or quick fix — because you understand yourself on a much deeper level and know how to build a lifestyle that truly supports your health long-term.

The course is hosted inside my private learning platform and includes all 12 weeks of guided content.

Enrollment is now open.

The Søberg® 12-Week Reset

I cannot wait to guide you through this journey!

— Dr. Susanna Søberg

You’ve probably seen it.

People stepping into ice baths after workouts.
After sauna.
After stress.
After everything.

Cold exposure has gone from a niche practice to a daily ritual for millions. And while that’s exciting—because yes, cold can be incredibly powerful—there’s a critical nuance missing from the conversation right now.

A nuance that could mean the difference between adapting… and blunting your progress.

Today, I want to explain what’s actually happening in your body when you use cold—and why timing matters far more than most people realise.

The promise of cold—and where it goes wrong

Cold exposure activates a powerful physiological cascade.

You get:

• Increased norepinephrine

• Activation of brown adipose tissue

• Improved insulin sensitivity

• A shift in your autonomic nervous system

These are real, measurable effects. And they’re part of why cold exposure has become so popular.

But here’s the issue:

Cold is not neutral. It is a stressor.

And like any stressor, its effect depends on when you apply it.

Read more

And for many people, it’s simply easier to start with than a traditional Finnish sauna.

The temperature feels more manageable.
The air is easier to tolerate.
And you don’t get that same immediate intensity when you step inside.

But this also creates confusion.

Because infrared is often described as a “gentler sauna.”

And physiologically, that’s not quite right.

What Makes Infrared Different?

A traditional sauna heats the air around you.

Infrared works differently.

It uses light to heat the body more directly.

That means:

• You can feel warm without extremely high temperatures

• The experience is more gradual

• And for many people, more tolerable

But the key difference is not just how it feels.

It’s how your body responds.

What Happens in the Body?

Even though infrared feels milder, there are still real physiological effects.

1. Circulation increases
Infrared exposure can help your blood vessels relax, which improves blood flow.
This is one reason it often feels calming.

2. Your body warms from within
Instead of being surrounded by very hot air, your body distributes heat internally.

3. You activate a stress response—just at a lower level
Like all forms of heat exposure, infrared creates a signal in the body.
But compared to sauna, that signal is usually smaller.

When Does Infrared Make Sense?

Infrared can be useful if:

• You’re new to heat exposure

• You don’t tolerate high temperatures well

• You’re focusing on recovery rather than intensity

• You want something you can do more consistently

And this is important:

• The best protocol is not the most extreme one

• It’s the one you can repeat

Sponsor

Today’s newsletter is sponsored by Boncharge.

They develop infrared sauna blankets and light-based tools designed to make infrared therapy accessible at home.

If you don’t have access to a sauna—or you’re just starting out—this can be a practical way to explore heat exposure in a more controlled way.

To get you started use SOEBERG10 on BonCharge.com

BONCHARGE

Final Thought

Infrared is not a replacement for sauna.

It’s a different tool.

Lower intensity.
Easier entry.
More accessible for many people.

But if you want to understand what it actually does—at the level of your cells, metabolism, and recovery—I go much deeper in the full article.

Read the full article

In the full piece, I break down:

• What happens inside your cells

• How infrared interacts with mitochondria

• Why circulation changes

• And how it compares to sauna from a metabolic perspective

The air feels lighter. The temperature feels more tolerable. You don’t get that same immediate intensity when you walk in.

And that matters.

Because if something feels too uncomfortable, most people won’t stick with it long enough to get any real effect.

But this is also where confusion begins.

Infrared is often positioned as a “gentler sauna.”
And physiologically, that’s not quite accurate.

It’s not just a softer version of the same thing.
It’s a different stimulus.

So instead of asking whether it’s “as good,” I think a better question is:

What does it actually do in the body—and when does it make sense to use it?

What Infrared Is Actually Doing (Beyond the Surface)

When you sit in an infrared sauna or use an infrared blanket, you’re not primarily heating the air around you.

You’re exposing your body to light.

And that light—especially near-infrared—interacts directly with tissue.

This is why the experience feels different.
The heat is not only external. It’s also internal.

But the important part is not the sensation.

It’s what happens at the cellular level.

Your Cells and Energy Production

Inside your cells, you have mitochondria.

This is where energy is produced.

And one of the most interesting findings in this space is that infrared light can interact with a specific part of the mitochondria—an enzyme called cytochrome c oxidase.

You don’t need to remember the name.
What matters is the effect.

Read more

People don’t struggle with stress because they are exposed to too much of it. They struggle because their system doesn’t resolve it.

This is an important distinction, and one that is often overlooked.

We tend to think of stress as something external — something that happens to us, something we accumulate, something we need to reduce. But from a physiological perspective, stress is not inherently negative. It is a signal. A deviation from the body’s current state, which initiates a response.

In a well-regulated system, that response resolves. The body returns, or adjusts, to baseline.

But when that resolution does not happen properly, something else begins to occur.

Over time, the system remains slightly activated. Not in a way that is always obvious, but in a way that gradually shapes how we feel, how we recover, and how we respond to new demands. It becomes a kind of background activation — subtle, but persistent.

This is where the problem sits.

Not in the exposure itself, but in the lack of resolution.

What I find particularly interesting is that when this begins to change, the shift is rarely dramatic. It does not feel like a breakthrough. It is much quieter than that.

People often describe it as a sense of stability. They recover a bit faster. They feel less reactive. There is less internal noise. The system becomes more regulated, but without a clear moment where everything suddenly changes.

And this is also why it can be difficult to recognise what is actually happening.

We are used to looking for intensity, for strong signals, for clear before-and-after moments. But physiological change does not always present itself that way. It often emerges gradually, through repetition, through exposure, and through the system learning to respond differently over time.

What has stayed with me most, however, is not just the data — it is the people.

Last year, after a talk, a man came up to me and said that he had learned more about health in that one hour than he had in the past ten years. That stayed with me, because it shouldn’t be that difficult.

Understanding your body should not feel fragmented. Understanding stress should not feel like something that only a few people have access to. And yet, for many, it still is. The information is scattered, the experiences are disconnected, and the results are often short-lived.

This has been a large part of what has driven my work.

Not just studying stress in controlled settings, but trying to understand how to translate that knowledge into something that actually works in practice — something that creates change over time, not just in a single moment.

This is also the foundation of what I am building with Thermalist®.

A way of taking these physiological principles and applying them in real-world settings — not as isolated experiences, but as structured processes designed to support adaptation over time.

If I have been quieter than usual recently, this is also part of the reason.

Much of my time has been spent working behind the scenes. Testing, refining, and trying to simplify something that is often made unnecessarily complex.

Because in the end, I do not believe that health should be that difficult.

For those of you working in spas, clinics, or performance spaces who are interested in how this can be applied in practice, science backed you can learn more about our first program the Thermalist® Method here:

Apply to license Thermalist

—

Dr. Susanna Søberg
Founder and CEO at Søberg Institute & Thermalist®

Stress is often framed as something to reduce — something we are exposed to, and ideally protected from. Lower cortisol, improve recovery, avoid overload. But this framing is incomplete, and in many ways misleading.

From a physiological perspective, stress is not inherently negative. It is a fundamental regulatory signal. It reflects a deviation from the body’s current state, and initiates the processes through which the body adapts.

What matters, therefore, is not the presence of stress, but how the organism responds to it over time.

Read more