Wim's Wise Words

The Researcher Who Changed Everything

Dr. Susanna Søberg's 2021 Cell Reports Metabolism study is the landmark research that turned cold exposure from folk practice into actionable science. Her work established the minimum effective doses—11 minutes of cold exposure per week, 57 minutes of heat exposure per week—for measurable metabolic benefits through brown fat activation. But what makes this conversation with Huberman essential is the nuance beneath those numbers.

The Søberg Principle Nobody Understands

Søberg's most quoted finding is "end on cold" when doing contrast therapy. The knowledge base confirms this across multiple studies: ending heat/cold sessions on cold maximizes brown fat activation and metabolic response. But practitioners misinterpret this constantly.

Ending on cold doesn't mean brief cold shower after sauna. It means allowing your body to rewarm itself naturally without active heating. The thermogenic cascade—shivering, brown fat activation, metabolic upregulation—happens during rewarming. If you sauna, plunge, then immediately get into hot shower or warm clothes, you've short-circuited the mechanism. The discomfort of rewarming isn't incidental. It's the adaptation.

Where Volume Matters More Than Intensity

Søberg's 11-minute weekly minimum is cumulative—not per session. Three sessions of four minutes each hits the threshold. What the research shows but people ignore is that longer, more moderate cold exposures (60-65°F for 10-15 minutes) produce more consistent brown fat activation than brief ice bath plunges.

The database contains studies showing that sustainable shivering is the key variable. Brief extreme cold triggers acute stress hormones but doesn't sustain shivering long enough for significant brown fat recruitment. You need thermal load that your body has to work against for minutes, not seconds.

This explains why winter swimmers—Søberg's primary research population—show such robust metabolic benefits. They're getting sustained cold exposure, often 5-10 minutes per session, multiple times per week, at temperatures that require continuous thermogenic response.

The Heat-Cold Synergy Paradox

What Søberg emphasizes but often gets lost is that heat and cold aren't just additive—they're synergistic when sequenced properly. Heat increases insulin sensitivity and cardiovascular function. Cold increases metabolic rate and fat oxidation. Together, properly timed, they create a metabolic flexibility that neither achieves alone.

But the research shows timing matters enormously. Heat followed by cold with natural rewarming creates different adaptations than cold alone or heat alone. The contrast creates a hormetic stress that signals your body to improve both heat and cold tolerance simultaneously. You're not just adapting to temperature extremes—you're expanding your adaptive range.

The Surprising Mental Health Connection

What doesn't get enough attention in Søberg's work is the dopamine and norepinephrine data. Her research shows sustained catecholamine elevation from regular cold exposure—not just acute spikes. This aligns with papers in our database showing that consistent cold practice correlates with reduced anxiety and improved mood regulation weeks into the protocol.

The mechanism appears to be both neurochemical and psychological. You're getting long-lasting dopamine from the cold itself, plus you're training stress tolerance in a controlled context. That combination transfers to life stress management in ways that pure pharmacological interventions don't replicate.

Where Søberg and Huberman Converge on Practical Application

Both emphasize sustainability over extremity. Søberg's protocols aren't about proving toughness—they're about finding the minimum dose that creates measurable adaptation, then maintaining it consistently. For most people, this means three to four cold sessions per week at tolerable but uncomfortable temperatures, combined with two to three sauna sessions.

The 57-minute weekly heat threshold can be distributed however your schedule allows. Four 15-minute sessions work. Two 30-minute sessions work. Consistency across weeks matters more than intensity within sessions. The adaptation accumulates slowly, then compounds.

Practical Threshold

Start with 11 minutes total cold per week. Distribute it across three sessions minimum. Temperature should be uncomfortable enough to trigger shivering within a few minutes but sustainable for the duration. End on cold and allow natural rewarming—no immediate heat. For heat, aim for 57 minutes weekly across two to four sessions.

Track sleep quality, mood, and energy more than body composition changes. Metabolic benefits appear weeks before weight changes. If you're sleeping worse, feeling more anxious, or chronically fatigued, you're overdoing volume or intensity. The protocol should feel challenging during execution but restorative across the week.

Søberg's research gives us the dosage. Your response tells you if you're taking the medicine correctly.