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∆U = Q – W

The First Law of Thermodynamics

Fuel – without it our engines don’t go.

When I first started running, I thought it really didn’t matter what I put into the tank as long as I put in something. I had long been a proponent of the idea that in order to maintain or lose weight, it was question of straight math – a matter of calories in vs. calories out.

I still believe that – to a degree. The first law of thermodynamics states that energy cannot be created nor destroyed, simply converted. You eat what you eat – you burn what you burn. So if you eat 2500 calories a day and burn 2500 calories a day, you will maintain your current weight. It’s simple math really: run a deficit, and the body has to come up with the calories from somewhere else (your fat stores – stored energy); run a surplus, and your body will have to find a place to store the leftover energy (your gut and/or thighs). There aren’t going to be any extra magical calories that pop out of or into the ether.

However, there are a couple of problems I see with this simplistic view.

First of all, the more efficient our engines become, I would assume the less fuel we actually need to accomplish the same activities. This would explain, in part, why some people I know actually gain weight when they are approaching the end of a marathon training cycle (literally 10 pounds). I understand that there is increased consumption from the intensified training followed by a taper, but I don’t believe that can account for all of the weight gain.

Second, I wonder just how accurate are the various ways we count calories. Do I personally really average about 140 calories per mile? Is the 200 calorie post-workout drink really 200 calories? Why does the treadmill tell me one thing and then dailymile tell me another? Truth is, we all burn our calories differently – some of us much more differently than others.

Finally, I’ve come to realize that the quality and/or form of fuel can make a huge difference. This last point could be its very own post, but suffice it to say that not all calories are created equal. Some will let you know when you are full, others will not. Which ones you eat will go a long way in determining how many calories you actually pour into your body.

The bottom line is that it is still a matter of calories in vs. calories out, however, the true, detailed formula is a lot more subtle than ∆U = Q – W. Each person must figure out how he or she burns their calories and then adjust accordingly.

*it was pointed out to me that psychology can have a huge impact on one’s fueling habits, and though I agree with this statement, I feel that if one is serious about the health benefits of exercise and healthy eating, one has to be willing and determined to conquer whatever psychological demons stand between him and his goal. Easier said than done and the topic of a stand alone post.

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