Andrew Huberman - Dr. Susanna Soberg

1) Dr. Susanna Søberg explains the physiological and psychological effects of cold exposure. She discusses how being submerged in cold water activates the sympathetic nervous system, causing an increase in catecholamines like dopamine, epinephrine, and norepinephrine. The degree of discomfort varies depending on an individual's current temperature and the temperature of the water. Dr. Søberg recommends getting uncomfortable in cold water to achieve the desired benefits, such as building resilience and adaptation. She explains that the hyperventilation response in the beginning can subside over time with training and adaptation, and emphasizes that cold exposure should be hard rather than enjoyable.

2) Susanna talks about the variability in people's ability to embrace the discomfort of the cold. Some people feel better in the cold, while others dread it. Those who avoid the cold tend to feel the cold pain more, as it triggers a sensitive nervous system. When comparing cold exposures, such as being outside on a cold day in shorts and a t-shirt versus cold immersion up to the neck, cold showers fall somewhere in between.

3) Susanna explains that cold showers activate brown fat which is responsible for regulating body temperature. She mentions that brown fat and muscles work together to keep us warm when our skin is exposed to cold. There are three pathways from the skin, the muscles, and adrenaline which activate brown fat. However, Andrew suggests that there are fewer studies on cold showers compared to cold immersion as it's challenging to control and observe human subjects in the laboratory. Dr. Søberg states that further studies are needed to explore these pathways in detail.

4) Susanna explains the importance of shivering and how it is an autonomic response that one should not be afraid of. Shivering is a normal response to cold exposure and it increases metabolism, which burns calories and increases insulin sensitivity. Shivering can be likened to training for cells, as it creates healthy stress called "homeostasis," which makes the cells more robust and better at adapting to future stressors. Cold exposure, therefore, is the same kind of training that one does when going to the gym.

5) Susanna discusses the long-term changes that occur with deliberate cold exposure. Similar to exercise, the discomfort provided by cold exposure, done safely, initiates a set of adaptations that improve health and make people feel better in the long term. These adaptations include an increase in catecholamines, dopamine, norepinephrine, and epinephrine, better insulin sensitivity, and a decrease in stress response. The body adapts to the cold exposure by activating brown fat, which creates more mitochondria and becomes more efficient at heating up the body. Capillaries in the skin improve their ability to constrict to prepare for the next cold exposure, making the body better able to handle future cold exposure sessions. Overall, these changes can lead to better health outcomes and overall wellness.

6) Susanna discusses the long-term outcomes of improving insulin sensitivity and glucose balance, including lower blood pressure and heart rate. She believes that Brown fat could be the missing link that explains why there is less inflammation in the body, as her study did not measure the presence of Brown fat. The podcast also includes a conversation about the benefits and biology of Brown fat, including its rich mitochondria content and its distribution throughout the body.

7) Susanna discusses the plasticity of brown fat, which can be grown and decreased in size in response to factors such as adrenaline levels and insulin sensitivity. Studies have shown that after the age of 40, there is an association between decreased brown fat and increased obesity, although it is not yet known whether decreased brown fat leads to obesity or vice versa. However, people who work outside or engage in physical labor may have more brown fat. Additionally, Dr. Søberg observes that elderly individuals who grew up doing manual labor or working on farms tend to be lean and fit, likely due to a lifetime of physical activity.

8) Susanna explains that cold temperatures can activate brown fat, which is involved in regulating body temperature and keeping humans in a homeostatic balance. She also confirms that face exposure to cold is enough to activate the brown fat and shows that activation is visible through an infrared thermography camera. Furthermore, she notes that brown fat is located close to the skin surface, which enables it to heat the body quickly. Dr. Huberman adds to the conversation by sharing his anecdotal experience working in a cold room in a laboratory, which helped him to adapt to the colder temperature and activate his brown fat, leading to weight loss and improved thermal regulation.

9) Susanna explains the Scandinavian practice of putting babies outside to sleep in the cold, which started in the 1950s in response to the tuberculosis epidemic. This practice makes people more resistant to the cold and improves the immune system. They also wear fewer layers before winter to prepare for the cold and more layers before summer to tolerate the heat better. Dr. Søberg notes that people from Denmark are very fit and healthy, partly because of their lifestyle, including cycling everywhere and swimming in cold water regularly.

10) Dr. Susanna Søberg discusses her research in the potential health benefits of exposure to cold. She explains that her initial study was meant to observe the minimum amount of exposure required to produce health benefits and the differences in white fat cellular structure before and after the exposure. She describes her personal experience going into cold water for the first time, noting that it felt uncomfortable during the experience but extremely invigorating and energizing afterward.

11) Susanna discusses her research on cold exposure and how she recruited a group of winter swimmers who have been swimming for two to three seasons to observe their adaptation to the cold. She wanted to do a proof of concept where the participants were already adapted to the cold and then compared them to a matched control group who were matched on diet and BMI. They also observed that women have more Brown fat than men and are thermo-comfortable at a higher temperature than men. The study was done to eliminate all the confounding factors which could have an impact on the results.

12) Susanna discusses the benefits of cold water exposure and how the body's parasympathetic nervous system is activated when submerged in cold water. She explains that the diving response is activated even when submerged up to the neck, and this can slow down oxygen consumption in the body to preserve oxygen and prevent hypothermia. Winter swimmers in Denmark were monitored for a study, where they climbed down a ladder into the cold water for one to two minutes and then took two sauna sessions per day, each lasting 10-15 minutes.

13) Susanna discusses her study on using cold and heat exposure for health benefits. The study involved participants doing multiple rounds of alternating between cold water and a sauna. The water temperature ranged from 2 to 15 degrees Celsius. The participants were allowed to go at any time during the day, and the study included measuring the impact on brown fat activity and metabolism. Besides measuring temperature, they also used pet MRI scanning to understand brown fat activity, and the results showed high brown fat activity during and after the stimulation.

14) Susanna explains how she measured the comfort level of participants in different temperature environments by asking them to rate their comfort level on a visual analog scale from one to 10. She also measured the shivering response of winter swimmers during cold exposure and compared it to their adaptation to cold water. The study showed that the winter swimmers had increased insulin sensitivity with lower insulin production and faster glucose clearance in the bloodstream, leading to better blood glucose clearance. High blood glucose levels can be toxic, especially to brain cells.

15) Susanna discusses the optimal amount of cold exposure for health benefits and the potential risks of overdoing it. She explains that becoming too cold-adapted can exhaust the cells and increase the risk of cardiovascular disease. The threshold for cold exposure is 11 minutes per week, divided into two or three sessions of one to three minutes each, or alternatively, three 20-minute sessions. It is beneficial to divide the sessions to achieve the autonomic stimulus, which stimulates the Hermetic response. Longer sessions might not be beneficial as shorter bouts act as stimuli.

16) Susanna explains her findings on the sleep quality of winter swimmers. Anecdotally, winter swimmers reportedly feel very comfortable during cold exposure and experience a good night's sleep, although she did not actually measure their sleep quality. Additionally, the winter swimmers in Denmark are comfortable with nudity during their swimming as it is part of their tradition, but newer clubs have implemented bathing suits due to the possibility of pictures being taken. Søberg also shares her personal use of sauna and cold exposure at home and during travel.

17) Susanna discusses the clothing optional cold plunge experiences at various banyas across the US and the common misconceptions associated with them. She emphasizes that these banyas promote health and wellness and there is no requirement to be naked. Furthermore, she highlights that there are several peer-reviewed studies on behavioral interventions for health, including deliberate cold exposure and sauna, the use of natural herbs and supplements, and psychedelics that are being adopted by mainstream medicine and pharma companies.

18) Susanna discusses the "soberg principle" which suggests ending on cold exposure to increase metabolism and activate brown fat cells. By ending on cold, the body must heat itself up requiring the activation of brown fat and muscles, leading to increased mitochondria in the cells, generating heat quickly and efficiently. Winter swimmers were physically warmer and had higher brown fat activation compared to the control group, indicating the potential benefits of this practice. The goal is to keep the body in a natural balance, and this natural stress of cold exposure can help achieve that.

19) Dr. Susanna Søberg discusses the practicalities of deliberate cold exposure, including questions about headaches that some people experience when doing cold immersion to the neck. She explains that a reason for keeping the head out of the water is that it could increase the decrease in blood flow to the brain further. She mentions a study from Denmark where cold water immersion decreased blood flow to the brain by around 30 to 40 percent. She also explains the importance of wearing a beanie during cold exposure to keep one warmer and avoid conditions such as brain freeze from wind. Overall, she suggests that people should know the information and evaluate what is best for them.

20) Susanna discusses the use of cold and heat exposure to improve health, specifically focusing on children and the unique considerations for their exposure. One study found that while children can defend their core temperature in the same way as adults, they have to use their muscles faster and therefore can't stay in the cold for as long. Dr. Søberg also notes that protocols can't be completely transferred from adults to children because children are smaller in mass.

21) Susanna discusses the differences in cold adaptation between children and adults, as well as the differences between male and female responses to cold exposure. She notes that children have a greater surface area to mass ratio, making them more vulnerable to hypothermia. Regarding the gender differences, women tend to have a higher metabolism in their brown fat and may need less exposure to cold to see benefits. Dr. Søberg emphasizes the importance of caution when approaching cold water and suggests starting with cold showers instead of jumping into natural bodies of water.

22) Susanna discusses how to do deliberate cold exposure for those who don't have access to cold plunges or saunas. She recommends getting in and out of cold water for short periods of time, as it is the change in temperature that strengthens the cells in our bodies by challenging them to adapt. By varying the temperature in the cold plunge or by leveraging the changing seasons, we can get the benefits of the cold without going to extremes. She also emphasizes that biology is a process rather than an event and that going from warm to cold and cold to warm is more important than hitting a specific temperature for a specific time.

23) Dr. Susanna discusses her ongoing study on deliberate cold and heat exposure, which looks at both men and women. While she can't share any concrete results yet as the data is still being analyzed, she emphasizes the importance of conducting such high-resolution studies given the lack of modern, detailed research in this area. Dr. Søberg also thanks the audience for inviting her on the show and for the opportunity to share knowledge about her research and insights on this topic.