Sweating Yourself Slim: The Truth About Perspiration And Fat Loss

Ahh, good ol’ perspiration, is there anything more indicative of a hard workout than a puddle of sweat under your toes? Well, actually yes, there is, so you can stop trying to impress people by leaving your salty excretions all over the gym.

Sweating (more properly called “perspiration”) is your body’s mechanism of keeping itself cool during times of increased body temperature. The antagonistic mechanism of sweating is shivering, whereby your body stimulates movement to generate heat when body temperature drops.

Many people infer that sweating is a sign of increased energy expenditure, but is this really a valid assumption? Seems like a sound supposition in theory, since heat is energy and sweating can be seen as a sign of expelling heat.

Alas, the actual physiological reasoning behind this theory is a bit more complex than if A=B and B=C, than A=C.  Moreover, the idea that sweating is a signifier of fat loss is a bit shortsighted. Let’s look at what sweating actually is and why you shouldn’t be so concerned about it one way or the other in regards to losing fat.

What is this salty discharge?

If you aren’t familiar with what exactly sweat is I’ll indulge you a bit. Analogous to other organisms with semi-permeable skin layers, our skin contains pores that allow the evaporation of fluid out of the body. Hence, the millions of sweat glands under the skin that humans are born with have the duty of excreting such fluids when the body needs to decrease temperature.

One of the main reasons sports drinks boast about their electrolyte content is that the body loses electrolytes through the process of sweating; therefore, sweat generally contains sodium, calcium, potassium and magnesium ions. The fluid is comprised almost entirely of water (~99%) and minute amounts of salt(s), lactate, urea, and trace metals (~1% combined). (1) The exact composition of human sweat varies based on several factors such as: what you have been drinking and eating, stress levels, how long you’ve been sweating, and a variety of others.

Does sweating equal fat (or even calorie) burning?

Aside from the fact that these beads of sweat don’t actually contain lipids (or calories for that matter), sweating itself is not a calorie-requiring process. Contrary to popular belief, sweating is actually less metabolically demanding than shivering. Thus, it’s actually more favorable (in terms of burning calories) to exercise in cold temperatures as opposed to doing the same workout in hot temperatures.

Coincidentally enough, obesity in the United States is significantly greater in in regions that have predominantly hotter weather. Conversely, states that have a cooler climate tend to be less obese. I’m not saying if you’re obese you should consider moving out of a hot climate in search of the Eskimos, but just some food for thought about the correlation between temperature and bodyweight.

The physiological reasoning behind this is that shivering is actually your body performing rapid, micro-contractions in an attempt to generate heat to warm yourself. The heat generated by these shivers actually burns a few calories, whereas sweating does not since heat isn’t being generated but merely diffused out of the body (in a matter of speaking). But the extent to how many more calories you are burning in a cold atmosphere compared to a warmer one is trivial at best.

Moreover, despite the extra (insignificant) amount of calories you may burn off working out in the cold, I would still advise working out in environments that are warmer simply because increased body heat promotes blood flow and vasodilation, both of which are conducive to muscle growth (not to mention better performance and reduced injury risk).

So why do I weigh less after I sweat a lot?

Simple, you’re losing water weight and electrolytes, not body weight. The idea that sitting in the sauna or wearing insulated clothing to increase the calories you’re burning is nonsense. These things serve merely to increase body temperature, which increases perspiration, not your energy expenditure (i.e. calorie burning).

Ok, but I heard sweating is good for releasing toxins/cleansing the body, is this true?

Another myth purported by cleanse-promoting quacks is that sweating is necessary (and encouraged) since it expels toxins from the body. Personally, I think the whole field of “cleansing” is pseudoscience, at best, but I digress. Toxin removal is relegated to your intestines and liver, not your sweat glands; so don’t try and justify taking a steam to “purify” your body of all the mercury from the canned tuna you choke down.

Parting words

Hopefully this has shed some light on what sweat actually is and what it does (and does not) achieve for us humanoids. If you see someone wearing an insulated body-suit in the gym trying to sweat their self thin, don’t be afraid to enlighten them of their foolishness. And unless you want to smell like a dead cow’s toe, I would advise taking a shower after you’ve worked up a good sweat.

References:

1. Sweat mineral-element responses during 7 h of exercise-heat stress," Int J Sport Nutr Exerc Metab 2007 Dec;17(6):574-82.