Dr. Susanna Soberg has built her career around a deceptively simple idea: that deliberate exposure to temperature extremes — cold and heat — triggers the same kind of adaptive resilience we see from exercise and fasting. Her research centers specifically on brown adipose tissue, the metabolically active fat that burns calories to generate heat. Her claim is that most of us have let this tissue go dormant, and that cold exposure is the most direct way to wake it up again.
This isn't fringe science. It's metabolic biology. And the implications for longevity are significant.
What strikes me about Soberg's work is how cleanly it connects to everything else we know. The two to five-fold increase in dopamine and norepinephrine from cold exposure — that neurochemical cascade — is the same mechanism Andrew Huberman has written about extensively. The sympathetic nervous system floods you with catecholamines. In the short term, this is neuroprotective and mood-elevating. Over time, the brain becomes more sensitive to its own feel-good signals.
And on the heat side, Rhonda Patrick's Finnish sauna research tells us that this isn't a slow, marginal process. Four to seven sauna sessions per week produces a fifty percent reduction in cardiovascular mortality. That's not a rounding error. These are effect sizes we associate with pharmaceutical interventions — except you're just sitting in a hot room.
What Soberg adds to this picture is the metabolic dimension. Brown fat isn't just a curiosity. It's a metabolic lever. Activate it regularly through cold, and you improve insulin sensitivity, raise resting metabolic rate, and reduce the risk of type 2 diabetes. Let it sit dormant — which most adults do, in temperature-controlled environments year round — and it diminishes. Use it or lose it. That's the principle.
There is remarkably little disagreement among researchers here on the core principle: hormesis works. Short, acute stress — whether from cold, heat, exercise, or intermittent fasting — builds resilience. The disagreement is in the dosing. Soberg leans toward shorter, more frequent cold exposures. Others advocate for longer sessions. The truth is probably individual — body composition, brown fat baseline, cold adaptation history all shape the optimal dose.
Start cold. End warm. Don't skip the finish. One of the most common mistakes I see is ending a cold plunge and immediately heading indoors to a heated room. Let your body warm itself — that active rewarming is where much of the metabolic benefit happens. Brown fat is doing its job in those minutes. Trust the process. And if you're adding sauna, separate it from your cold plunge by a few hours when possible, so each stressor gets its own full adaptive response.
Soberg mentions that women tend to carry more brown fat than men — likely due to differences in body composition and hormonal environment. This is underexplored in the popular conversation around cold therapy, which skews heavily male in its examples and protocols. But it suggests that women may have a metabolic advantage in cold adaptation that hasn't been fully mapped yet. The sex-specific research here is still early, but it's one of the most interesting threads in the entire field. Watch that space.
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