Infrared sauna: 1000 Calorie myth

Claim that an infrared sauna can burn 600 Calories per session (or even 1000) is one of the most widespread arguments about infrared sauna benefits for weight loss and cardiovascular system training. It is evident if you search for ‘(1000|600) calorie infrared sauna’ in Google. Many infrared sauna sellers, even long-established ones, have this claim written on their website. So many voices supports it. How can than be untrue? And still it is untrue, and in this article I’m going to show you why.

Do you really understand what ‘burning 1000 Calories’ mean?

To understand, what ‘calories burned’ means, lets look deeper at a well-known statement, for example: “Running burns 500 calories in an hour”. Do you fully understand this statement? If you say its easy, 500 calories is 500 calories, thats all, let me question you a bit:

  • What it a Calorie?
  • Why it is written with first capital letter, Calorie, not just calorie?
  • What means “burns”?
  • Does it matter if I will run uphill or downhill? Will I burn the same amount of calories?

And that is just for starters. If you find questions above too easy, here is some harder ones:

  • Will I burn more calories if I weight 100 kg (approx. 200 lbs) instead of 75 kg (approx. 150 lbs)?
  • Will I burn more calories if outside temperature is 30 C (86 F) instead of 20 C (68 F)?
  • When will I burn more calories – in first on in second half of an hour?

To understand statements about Calorie expenditure clearly one should be able to answer this questions. The main word in this statement is Calorie. Calorie is a unit of energy, as Joule is. It equals 4.187 kJ (kilojoule). So if you have an electric fan which power is 1200 Watt (which means it consumes 1.2 kJ per second) you can say that your fan consumes 0.287 Calorie per second. Why Calorie with capital letter? Well, it is because of a little mess in units of measuring energy. Initially, calorie was defined as amount of energy required to heat one gram of water by one degree C. It is also called ‘small calorie’. The ‘large calorie’ or Calorie, is energy required to heat one kilogram of water by one degree C. 1 Calorie (Cal) = 1 kilocalorie (kcal) = 1000 calories (cal).

Burned calories is amount of energy expenditured by human metabolism over period of time (it is called metabolic rate). It is important to understand that human can not only lose heat to environment, but, if environment is hot, he also gains heat. Heat can accumulate in a human body, raising body’s temperature. So to determine amount or burned calories one should subtract amount of energy gained from amount of energy lost and to add the amount of energy stored in a body.

Amount of calories burned depends on how hard our body is working (muscles, cardiovascular system, etc.). If activity is hard, more energy is required, more calories are burned. Running uphill or at higher speed leads to more calories burned. Outside temperature is not so important factor for metabolism rate – it will go up only slightly, because body will increase blood flow for better cooling. Exercising in a very hot environment can lead to overheating because body will not be able to release large amount of heat produced by exercise, and internal temperature will raise. During warm-up phase amount of heat produced gradually increases to a level required by activity.

Returning to infrared sauna session

With proper understanding of calories and energy processes in a human body, let’s examine an infrared sauna session. To find the energy really produced by our metabolism (and thus, by spending fat, glucose and protein molecules), we need to estimate energies:

  • received energy from environment;
  • energy lost to environment;
  • energy stored in a body, raising temperature above normal.

Energy received in an infrared sauna comes mainly from infrared heaters, but also from air which is above normal body temperature. As a max value I will get the power of typical 2-person sauna – 1200 Watt, which is approx. 500 Calories per half an hour (remember, calorie is energy). How much energy your body really receive depends on many factors – sauna size, air flow and is much lower than 500 Calories (I will take 250 for estimate). Since your body temperature is lower than sauna air temperature, you cannot lose heat just by convection, conduction or radiation – and your body uses another effective way to cool down – sweating. Evaporation of one gram of sweat cools your body by approx. 0.6 Calorie. Typical given amount of sweat produced during a sauna session is 500 gram. If all of these 500 grams evaporate, you will lose 300 Calorie of heat. But apparently, sweating in a sauna is so intensive that not all sweat evaporates – it flows down from your body (let’s take 200 Calorie for estimate). And greater amount of sweat produced (2-4 times, by claims of some promoters) won’t help to get rid of more heat, because extra sweat won’t evaporate – it will stay on a towel or sauna bench, or will be washed off in a shower after session.

Extra heat stored in a human body during infrared sauna session can be very roughly estimated, assuming that heating body by 1 C requires the same energy as heating equal mass of water by 1 C. Since core temperature rise is not typically exceed 2 C, for a 75 kg man amount of heat stored estimates as 75*2 = 150 Calorie.

This very rough figures gives an estimate: 200 Calories (lost) + 150 Calories (stored) – 250 Calories (gained) = 100 Calories produced by metabolism. I repeat again, this estimate is very rough, but its clear that 1000 or even 600 Calories are nowhere to be found. Indeed, how can you expect your body metabolism spend 600 Calories if you’re just sitting for half an hour, comparing to running or weight lifting?

So, where 1000 (600) Calories came from?

As any claim, ‘1000 Calories per session’ must be supported either with experimental facts (independent measurements of energy expenditured while taking an infrared sauna) or with some statements which are known to be true and from which ‘1000 Calories’ claim can follow. What arguments or references do infrared sauna promoters provide? There is only one explanation is given in promotional texts (if given at all), and its roots go to the article “Infrared thermal system” by Dr. Aaron M. Flickstein. Here is a citation from this article:

Guyton’s Textbook of Medical Physiology reports that producing one gram of sweat requires 0.586 kcal. The JAMA citation above goes on to state that “A moderately conditioned person can easily sweat off 500 grams in a sauna, consuming nearly 300 kcal – the equivalent of running two to three miles. A heat-conditioned person can easily sweat off 600 to 800 kcal with no adverse effect.”

Conclusion of the cited paragraph is based on two statements:

  1. Producing one gram of sweat requires 0.586 kcal (which is equivalent to 0.586 Calorie).
  2. A person can sweat off 500 grams and more (2-4 times) in an infrared sauna.

From this follows, that if a person produced 500 grams of sweat in a sauna, he lost 500*0.586 = approx. 300 Calorie. If there was 1500 grams of sweat, then 900 Calorie will be lost. But this logic is wrong, because the first statement is simply not true. Guyton’s Textbook of Medical Physiology doesn’t say that “producing one gram of sweat requires 0.586”. Current edition of this book say:

Evaporation is a necessary mechanism of heat loss at very high temperatures. As water evaporates, 0.58 Calorie of heat is lost for each gram of water that is converted into the gaseous state. The energy to change water from a liquid to a gas is derived from the body temperature.

In a sauna, when sweat evaporates, it cools body from heat gained not only by metabolism, but also from infrared heaters. You get energy from heaters and give it back by evaporating sweat. Your metabolic rate rises only slightly, when body switch on its cooling processes. So amount of energy coming from the fat is not rising significantly.
Why this wrong claim is so popular on Internet? Probably because it looks so attractive, and website often copy it from each other. Many infrared sauna promoters don’t care if its true, but they care about sales. So this claim, with reference to such authority as JAMA, took a big part in their argumentation about infrared sauna benefits.

Another cause is that Internet is much less controlled. When it comes to advertising on TV, such claims can be questioned – look, for example, here:

Keep your eye on the ‘1000 Calorie’ claim when looking for an infrared sauna on the Internet. If a seller has such claim on a website, it doesn’t necessarily mean that their infrared sauna is bad, but it is certainly an indicator that you should be more careful when buying from such a shop.

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