An hour sitting in 40°C water burned 61 more calories than resting
In this 2017 study in the journal Temperature, researchers measured the energy 14 men burned while heated in water and while cycling. It gives the cleanest number we found for what heat alone costs the body.
The paper
The effect of passive heating on heat shock protein 70 and interleukin-6: A possible treatment tool for metabolic diseases?
Faulkner SH, Jackson S, Fatania G, Leicht CA. Temperature, 2017;4(3):292-304.
See the study at a glance
- Design
- Randomized crossover study
- People
- 14 men
- Who they were
- Lean men (average BMI 23.5) and overweight men (average BMI 29.2).
- What they did
- An hour in 40°C water on one day and an hour of moderate cycling on another. The cycling was set to raise core temperature by the same amount. Researchers worked out energy use from the gases people breathed in and out (indirect calorimetry).
- How long
- Two separate sessions
These numbers came out of it
+61 kcal/h
An hour of sitting in 40°C water burned 61 more calories than resting. That's a 79.5% rise.
+556 kcal/h
An hour of moderate cycling that raised core temperature as much burned 556 extra calories.
63.4 vs 58.5
Lean men burned 63.4 extra calories in the hour of heating and overweight men 58.5.
The researchers did this
In counterbalanced order, 14 lean or overweight men spent an hour sitting in 40°C water on one day and an hour cycling at a moderate pace on another.Source 1 · Crossover trialThe effect of passive heating on heat shock protein 70 and interleukin-6: A possible treatment tool for metabolic diseases?Faulkner SH, Jackson S, Fatania G, et al.. Temperature, 2017.Read the paper ↗PubMed ↗ The ride was set to raise core temperature as much as the hot water did, and energy use was measured by indirect calorimetry.
In the hot water the men used 79.5% more energy than at rest. That came to an extra 61.0 kcal an hour, and cycling added 556.3 kcal an hour.Source 1 · Crossover trialThe effect of passive heating on heat shock protein 70 and interleukin-6: A possible treatment tool for metabolic diseases?Faulkner SH, Jackson S, Fatania G, et al.. Temperature, 2017.Read the paper ↗PubMed ↗
Over the hour of heating, lean men burned an extra 63.4 kcal and overweight men an extra 58.5 kcal. At rest the men burned about 1,811–1,874 kcal a day.Source 1 · Crossover trialThe effect of passive heating on heat shock protein 70 and interleukin-6: A possible treatment tool for metabolic diseases?Faulkner SH, Jackson S, Fatania G, et al.. Temperature, 2017.Read the paper ↗PubMed ↗
The researchers mainly wanted to know whether heat shock protein 70 and interleukin-6 could serve as tools against metabolic disease.Source 1 · Crossover trialThe effect of passive heating on heat shock protein 70 and interleukin-6: A possible treatment tool for metabolic diseases?Faulkner SH, Jackson S, Fatania G, et al.. Temperature, 2017.Read the paper ↗PubMed ↗ They collected the calorie figures during the same sessions.
The study can't tell you these things
- It used hot water. We found no similar calorie-measuring study of a dry sauna.
- All 14 participants were men.
- An hour in 40°C water is longer than a typical sauna round, so a shorter session would cost fewer calories.
- It measured one-off sessions and didn't track weight or body fat.
We cited these sources
- 01Faulkner SH, Jackson S, Fatania G, Leicht CA. The effect of passive heating on heat shock protein 70 and interleukin-6: A possible treatment tool for metabolic diseases?. Temperature. 2017;4(3):292-304. doi:10.1080/23328940.2017.1288688 PMID 28944271