Thermodynamics of weight loss & other considerations

What? Thermodynamics?

One of the most fundamental laws of thermodynamics is that matter and energy are conserved. How energy and matter are related and spent in the human body is a matter of some interest.

When we look at the human body, we are dealing with a system which stores energy in the form of fat. If we want to reduce the amount of stored energy, this generally means we need a net negative energy balance - spending more than we take in. Hence the classic advice "eat less, exercise more."

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The human system

The human body is a system like any others. It has inputs and outputs.

Inputs:

Food
Water
Vitamins and minerals
Heat
Oxygen

Outputs:

Mechanical energy
Heat
Solid and liquid wastes
Sweat (water and minerals)
Carbon dioxide

In nearly all conditions, the net flow of heat is out of the body. When we talk about weight management, we're worried about how much energy is being stored within the system. Extra energy is turned into body fat (and body fat back into extra energy) at 3500 kilocalories (food calories) per pound.

Heat leaves the body

Sweats and chills

The loss of heat due simply to a body keeping itself warm is proportional to the surface area of the body, and the temperature difference between the body and its surroundings.

If the air in contact with your skin is 75 degrees Fahrenheit, and your surface skin temperature is 90 degrees Fahrenheit, you'll burn about 30% more energy keeping warm at 70 degrees.

At normal temperatures, your basic operating metabolism will typically account for around 1500 kilocalories per day. If you increase this by 30%, that's 450 kilocalories per day - so you can indeed "freeze your ass off."

Just bear in mind that under anything resembling normal circumstances, this won't account for more than a few hundred kilocalories (food calories) per day, and you'll usually make up for it with an increased appetite.

Contrary to the mythology that has cropped up, sweating more does not mean you lose more weight! In fact, while you may lose a little more water weight temporarily wearing a sweatsuit - or even a "sauna suit" or some other extreme heat-retaining garb - you will spend less energy heating yourself. This means that if anything, you're burning less fat, not more, when you try to maximize sweat.

Swimming pools

Swimming pools are fantastic for several reasons. The most obvious is that since people and water are very close to the same density, their effective weight is reduced. This means next to no stress on the joints, and ease of motion for even those who are both severely overweight and out of shape.

Less obvious is that water and skin conduct much better than air. Even the warmest swimming pool leaches a lot of heat out of your body through conductivity.

The high resistance of water means that even as simple an activity as walking through the shallows of a pool, or splashing around with your kids, is exercise. You don't have to be swimming laps to get a workout in a swimming pool.

For these reasons, whenever anybody asks how to lose weight, I always mention swimming pools.

	U.S. Divers Mercury Shorty Adult Wetsuit Price: $69.99
	U.S. Divers Mercury Full Adult Wetsuit Price: $89.99
	Aqua Sphere Stingray 2mm Youth Core Warmer Price: $29.99
	Speedo Aquatic Xtra Life Lycra Conservative Ultraback Swimsuit Price: $61.99
	Columbia Whoosh Set Boys Toddler Price: $89.99

Disclaimer

Consult a physician before making any dramatic changes to your diet and activity levels. No, seriously. I've seen what happens when someone doesn't. It can be quite dangerous.

The above article is not a comprehensive guide to weight loss. And please don't give yourself hypothermia. Moderation is critical in all things relating to fitness and health.

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