The Søberg Principle

The Søberg Principle: When using deliberate cold exposure to increase your metabolism, minimize hot showers & sauna after the last cold exposure. Forcing your body to re-warm on its own is a major component of the metabolism & brown fat (healthy, thermogenic fat) stimulation. - Dr. Andrew Huberman

The Summary From Dr Søberg's research concludes:

The Scandinavian winter-swimming tradition involves brief immersions in cold water complemented by hot sauna sessions, potentially affecting body temperature. We examined experienced winter-swimming men, engaging in this activity 2–3 times per week, to investigate thermogenic brown adipose tissue (BAT). Our findings indicate that winter swimmers experience a lower thermal comfort state compared to controls, reflected in lower core temperatures and no BAT activity. However, when exposed to cold, winter swimmers exhibit greater increases in cold-induced thermogenesis and supraclavicular skin temperature, with BAT glucose uptake and muscle activity comparable to controls. Furthermore, all subjects display reduced supraclavicular skin temperature during the night, with a distinct peak occurring at 4:30–5:30 a.m. in winter swimmers. These insights contribute to our understanding of BAT's role in adult human thermoregulation, suggesting both heat and cold acclimation in winter swimmers and highlighting winter swimming as a potential strategy for increased energy expenditure.