Does Bikram Yoga or hot yoga burn more calories than regular yoga? Does sweating more in a hot gym mean you are burning more calories? Can I lose weight in a sauna?
No, no and no…
I apologize in advance as this topic will ruffle some feathers but there is only one scientifically valid method of looking at this topic and it is often manipulated by health clubs, spas and health practitioners to serve the purpose of selling programs. Sometimes I think the health practitioner even believes it themselves as they aren’t smart enough to validate their claims scientifically. That may be even scarier.
We have all heard these myths over the years and they tend to reinvent themselves in new training routines and methods constantly. They are documented by anecdotal evidence of weight loss as someone sweats off all this water, gets on a scale and declares victory with 2-3 pounds of weight loss!
The reality is that the weight loss is virtually all water and not fat. You are now dehydrated and in a weakened and potentially dangerous state. I am not saying that sweating has no purpose as indeed it does. It allows the body to remain cool and keep from overheating when we are performing physical labor and it helps to detoxify the blood system as the skin is the largest organ in your body. But, even then, the amount of detoxification is not nearly as significant as the liver or the kidneys. If you stop sweating you are not likely to die from toxins but if your kidneys stop filtering or your liver stops cleaning out the blood system you will indeed die. The skin only plays a supportive role in detoxification.
As for the weight loss, 1 gallon of water weighs 8.345 Pounds. A gallon of water is equal to 128 ounces. Therefore, we can calculate the potential for weight loss or gain through drinking or sweating. So to put it another way, a 32oz Big Gulp Soda drink weighs approximately 2.08 pounds. So right after you get done slugging one of those down you will immediately see a 2 pound weight gain not to mention the fat you are going to accumulate from the conversion of glucose/fructose (sugar) to triglycerides (fat). A Big Gulp of Coca Cola by the weight contains 91 grams of sugar and 364 calories, a whole other conversation.
So how much do you perspire on a normal day?
Anywhere from a few ounces to a few hundred ounces. So sweating off a pound or two with a really hard workout or in a sauna is no problem for most average sized individuals. The problem is created if you fail to replace this water loss and you begin the process of dehydration, a dangerous condition which can cause fatigue, illness and sometimes death.
So, is there a difference between sweating from external heat conditions rather than from performing physical labor?
I have to go into a bit of science here but the lesson is that generating heat externally rather than internally is different. In fact the interpretation of such phenomenon is misunderstood by most individuals, many health practitioners and generally non-scientists.
Misinformed proponents of external heat sources such as hot yoga, plastic sweat suits, saunas… claim that it is an effective method for considerably raising the rate of energy expenditure in the body when in fact it is not.
This statement is based on a scientific calculation of the amount of energy absorbed by sweat evaporating from the skin. That energy is equivalent to the “latent heat of vaporization of water”, which is 539 kcal/kg (2260 kJ/kg). The source of this energy is confused by most individuals and many health practitioners to be body energy stores, while the source is in fact the excessive heat absorbed from the external environment. The body reacts to the excess heat flux by increasing perspiration. This process does not increase body heat generation and caloric burn rate.
So how does that apply to something like hot yoga in plain English?
In actuality, following our science above, hot yoga does not really burn more calories as the mechanism for cooling down the body from external heat is very different than the mechanism that creates heat and sweat in order to cool the body because it is working hard. For example, I can work you to death and have you drowning in your sweat but the likelihood of your core temperature rising and or giving you a heat stroke as long as you are not in the sun is slim to none, it is almost impossible provided you are re-hydrating properly. But if I heat you up environmentally as is done in the widely popular Bikram yoga, then the chances of killing you from things like heat stroke are extremely high. The body is sweating for different reasons.
So sweating does not burn extra calories, the cause of the sweat does. Therefore if you sweat because the body is working hard and trying to cool itself down, it is the act of “working hard” that burns the calories not the sweat. The sweat is just a cooling mechanism. Think of it as a result or symptom and not a cause. But if you are sweating because you are sitting quietly in a room with a temperature of 105 degrees, you are burning very few calories even though you are sitting in a pool of sweat as your body is really doing no work.
Sweating is not a reaction that causes increased weight loss, it is the work effort that causes the sweat that increases real weight or fat loss. Sweating in general for any reason causes water weight loss which is quickly reversed when you begin re-hydrating again. If this weight loss from heat myth were in fact true, we could all sit in a sauna and get skinny… wouldn’t that be easy!
So the answer is that Bikram yoga or hot yoga, saunas, plastic sweat suits or just roasting in the hot sun burns the same amount of calories as regular yoga or any other comparable activity. In fact, I could make a case that the heat reduces your sustained work effort and therefore may actually reduce your ability to work harder and therefor reduce the amount of calories you are able to burn by cutting your duration short due to fatigue.
If someone would like to challenge this claim we have a $15,000 machine that measures caloric burn rate exactly which we could use to measure the activity. In fact we could bring in an expert health practitioner and get an independent and objective answer but you know what that answer will be already.