Topic: Cold and heat
Cold, heat and evolution: what the evidence says
Everything this site carries on cold and heat, gathered in one place: the book's chapters and where they say to start, every popular claim they grade, and the reference topics and terms behind them.
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Where does the book say to start on cold and heat?
Chapter 9: Heat and Cold
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.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 elseHeat: a sauna or a hot bath, a few times a week, if you have access and enjoy it
EmergingEvidence grade: Emerging. Early, small, animal-only, or actively contested.
Which popular claims about cold and heat hold up?
Do cold plunges do anything?
A narrow effect on heat regulation; nothing on fat loss.
EmergingEvidence grade: Emerging. Early, small, animal-only, or actively contested.for bothDoes a cold plunge after lifting hurt muscle growth?
Wrong if building muscle is the goal.
ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.Does a cold plunge burn fat? Brown fat, sized honestly
Oversold. Mild cold may nudge insulin sensitivity in tiny trials, but it will not move your weight.
ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.that the claim is oversoldEmergingEvidence grade: Emerging. Early, small, animal-only, or actively contested.for the insulin effectDoes a cold plunge raise dopamine 250%? The study behind the number
A real number, misapplied. Enjoy the jolt if you like it, without expecting a chemical dose.
EmergingEvidence grade: Emerging. Early, small, animal-only, or actively contested.Is 11 minutes of cold and 57 of heat a week optimal?
Not a protocol.
EmergingEvidence grade: Emerging. Early, small, animal-only, or actively contested.
What does the body expect, and what does it get now?
The mismatch cards of the reference topics behind these chapters, as the library states them.
Topic 25: The Thermoneutral Trap
ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.Thermoregulation: brown fat, muscle heat, skin blood flow, and the heat shock response.
- What it expects
- A day and a year that leave the thermoneutral band: cold mornings, hot afternoons, cooling nights.
- What it gets
- 18°C to 25°C indoors, all year, for about 87% of the time.
- What happens in the gap
- Cold-recruited tissue and whole-body acclimatization fade within a few years of the signal stopping, as the haenyeo showed, though the metabolic cost is small.
Topic 41: The Handrail II: Light, Sleep, Temperature, Nature
ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.The circadian clock, thermoregulation, and the stress-recovery loop, all driven by environmental signals rather than conscious effort.
- What it expects
- Thousands of lux by day, near-total darkness at night, a temperature that falls after sunset, occasional cold and heat, and daily hours outdoors.
- What it gets
- Under 1,000 lux of waking light in the week the campers spent at home, evenings in the 30 to 300 lux band the clock reads most steeply, a thermostat that never moves, and most of a life indoors.
- What happens in the gap
- The clock drifts later and flattens, sleep timing scatters, and systems tuned by temperature and daylight have nothing to tune against.
Terms
The chapters and reference topics on this page cite 74 distinct works, each listed on its own page and in the source register. Educational content, not medical advice; read the disclaimer.