The claim: Cold plunges
Do cold plunges do anything?
A narrow effect on heat regulation; nothing on fat loss. Evidence grade: Emerging for both.
Published Updated
Chapter 2's table of nine claims
A narrow effect on heat regulation; nothing on fat loss
The evidence
Eight Scandinavian winter swimmers, compared with eight controls, regulated body heat differently and made more heat in the cold. The study found no increase in brown fat and says nothing about weight loss. Chapter 9 gives the cautions about cold shock and the heart.24
Where the book tests it
What the book recommends instead
Let your home move a little: cooler rooms in winter, and a bedroom that cools at night
EmergingEvidence grade: Emerging. Early, small, animal-only, or actively contested.How: in winter, set the thermostat around 64 to 66°F and add a sweater rather than a degree; turn the heat down at bedtime so the bedroom cools overnight (Chapter 8 covers sleep). Why: a few weeks of mild cold grew brown fat and improved insulin sensitivity in tiny trials. Safety: the World Health Organization treats 64°F as a safe indoor floor in cold seasons, and older people, infants and anyone with heart or lung disease may need it warmer.
End your shower with thirty seconds of cold, if you like it and your heart is healthy
ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.for fewer sick daysEmergingEvidence grade: Emerging. Early, small, animal-only, or actively contested.for anything elseHow: finish a normal warm shower with thirty seconds of cold; longer did no better. Breathe slowly through the first gasp. Why: in the one large trial, it cut sickness absence by about three in ten, though not illness itself. Safety: with heart disease or an irregular heartbeat, ask a clinician first.
Related claims
- Does a cold plunge after lifting hurt muscle growth?Wrong if building muscle is the goal.Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
- Does a cold plunge burn fat? Brown fat, sized honestlyOversold.Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
- Does a cold plunge raise dopamine 250%? The study behind the numberA real number, misapplied.Evidence grade: Emerging. Early, small, animal-only, or actively contested.
- Is 11 minutes of cold and 57 of heat a week optimal?Not a protocol.Evidence grade: Emerging. Early, small, animal-only, or actively contested.
Sources
Chapter 2's table of nine claims
- 24.Søberg, S., et al. (2021). Cell Reports Medicine, 2, 100408 (Scandinavian winter swimmers combining cold water and sauna, 8 against 8 controls; do not read as more brown fat)
Note numbers are those of Chapter 2, What Your Body Expects, and How to Trust This Book.
This verdict is one of nine in the table Chapter 2 uses to show how the book judges a claim: find the primary study, and grade the claim by what it measured. The grade rates the evidence behind the verdict, by the book's stated method.
Educational content, not medical advice. Disclaimer.