“End your sauna session on cold to burn more fat.”

The research found this

Susanna Søberg's team published a study of Danish winter swimmers in 2021, and Andrew Huberman named a rule of ending on cold after her in a 2022 podcast episode.1Source 1 · Cross-sectional studyAltered brown fat thermoregulation and enhanced cold-induced thermogenesis in young, healthy, winter-swimming menSøberg S, Löfgren J, Philipsen FE, et al.. Cell Reports Medicine, 2021.Read the paper ↗PubMed ↗2Source 2 · PodcastUsing Deliberate Cold Exposure for Health and Performance (episode 66)Huberman A. Huberman Lab podcast, 2022.Read the page ↗ People now call it the Søberg principle.

The full text of Søberg's paper never mentions finishing on cold, and no experiment in it combined heat and cold.1Source 1 · Cross-sectional studyAltered brown fat thermoregulation and enhanced cold-induced thermogenesis in young, healthy, winter-swimming menSøberg S, Löfgren J, Philipsen FE, et al.. Cell Reports Medicine, 2021.Read the paper ↗PubMed ↗ The authors speculated that getting used to 57 minutes of sauna a week might explain why the swimmers ran cooler over 24 hours and showed no brown fat activity at a comfortable temperature.

A 2013 meta-analysis pooled trials in which people alternated between hot and cold water. It noted whether each trial ended hot or cold and never analyzed the results that way.3Source 3 · Meta-analysisContrast Water Therapy and Exercise Induced Muscle Damage: A Systematic Review and Meta-AnalysisBieuzen F, Bleakley CM, Costello JT. PLoS ONE, 2013.Read the paper ↗PubMed ↗ A 2026 review gathered 21 studies of alternating hot and cold and found none that measured energy use or brown fat. The review did notice that blood pressure fell after sessions more often when heat came last, though the authors pieced that pattern together by comparing different studies.4Source 4 · Systematic reviewCardiometabolic effects of contrast therapy: A systematic reviewde Haan V, Plasqui G, Pallubinsky H. Experimental Physiology, 2026.Read the paper ↗PubMed ↗

Cold raises energy use both in the water and during rewarming. After 48 minutes of cycling and a seated rest, 21 trained men sat waist-deep in 10°C water for 15 minutes. At the end of the soak they were using 7.16 ml of oxygen per kilo per minute, against 4.83 without it.5Source 5 · Crossover trialMechanism involved of post-exercise cold water immersion: Blood redistribution and increase in energy expenditure during rewarmingGiraud D, Pomportes L, Nicol C, et al.. Temperature, 2024.Read the paper ↗PubMed ↗ That difference works out to roughly 0.8 kcal a minute at that point, and the authors called the rewarming that followed metabolically costly.

In a 2026 trial in Wales, every sauna break on the dip day began with 90 seconds in 19.9°C water, so the last hot round was followed by cold. Fifteen minutes into recovery, core temperature on the dip day ran 0.63°C lower than on the air-only day. The study didn't measure energy use.6Source 6 · Crossover trialThermal and cardiovascular responses to sauna are attenuated by adding cold water immersion to cooling breaksOwen TF, Giles CJ, Leaney SF, et al.. Experimental Physiology, 2026.Read the paper ↗PubMed ↗