Dr. Susanna Søberg is the person who made it onto every biohacker's protocol card with two numbers: 11 and 57. Eleven minutes of cold water per week. Fifty-seven minutes of sauna. Those are the minimally effective doses that emerged from her PhD research — the thresholds at which the metabolic and brown fat benefits become statistically meaningful. And the best news? Most people are already spending more time than that.
But the numbers are almost beside the point. What makes Søberg's work distinctive in our knowledge base is the mechanistic depth. She doesn't just say cold water activates brown fat — she explains that brown fat is genuinely metabolically active tissue, pulling glucose and fatty acids from the bloodstream to generate heat. This means cold exposure is doing what exercise does: it's clearing glucose. For anyone with metabolic concerns — insulin resistance, pre-diabetes, even just the post-meal glucose spike everyone's now tracking — this is a pharmacologically interesting mechanism available to everyone with a cold shower.
We have her PhD research featured in several places across our database, and the conversation that complements this one most directly is her appearance on The Proof podcast, where she goes deep on the brown fat activation timeline. A key finding that gets underreported: the metabolic effects of cold exposure don't disappear the moment you warm up. Brown fat activation has a lingering afterburn. This is why Søberg recommends finishing on cold — not to be heroic, but to allow the thermogenic process to run its full course rather than cutting it short with warmth.
This is the Søberg Principle, and it runs counter to what most spas and wellness centres do. They put people in cold water and then immediately into a warm shower or robe. Søberg's research suggests this shortcircuits a significant portion of the metabolic benefit. The shivering, the rewarming from within — that's where the brown fat really earns its place.
What I find genuinely surprising, after reading across this entire knowledge base: we have probably 50 hours of podcast content featuring Huberman, Attia, Patrick, and others discussing cold exposure. The Søberg Principle — end on cold, let the body rewarm itself — is one of those recommendations that most people hear but don't follow. It's uncomfortable. It requires a few minutes of mild misery. But the metabolic payoff for those minutes appears to be disproportionate to the discomfort.
Her other insight worth preserving: the brain chemistry shift is real and durable. Regular cold water immersion is associated with reduced anxiety and improved mood over time. This isn't anecdote — it appears in multiple RCTs and her own data. If you're only ever doing cold water for the metabolic benefits, you're leaving the psychological dividend on the table.
Practical recommendation: two to three sessions of cold water per week (minimum two minutes each at genuinely cold temperatures — not a cool shower), complemented by two sauna sessions of 20 to 30 minutes each. Always end on cold. That's the protocol. It's simpler than most people expect, and backed by the most methodologically rigorous research in this entire category.