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Energy Balance

The Thanksgiving feast was delicious and the leftovers were too. I’m certain my calorie intake over the past week is quite out of balance with my use of energy.

A wooden kitchen match, burned entirely, gives off approximately on British Thermal Unit (Btu) of energy. One Calorie is the energy equivalent of burning four kitchen matches.

Normally, I do pretty well at balancing the energy I take in while eating with the energy I use for all my activities. We often think only of exercise as “burning calories,” butwe use energy 24/7 while breathing, eating, walking and sleeping. I tend to not keep track of calories or my weight, though I know many who do, however I do keep a rough estimate of my caloric balance. I use measures  such as  do my pants feel too tight or have I enjoyed a long walk today? Even by my rough calculations, I know I took in more energy over these holidays than I’ve expended!

As we’ve discussed here in the past, we can measure heat in various units including a British Thermal Unit (Btu) or a calorie (c). A Btu is the amount of energy required to raise a pound of water by one degree Fahrenheit. A wooden kitchen match, when burned entirely, is roughly one Btu. If we were able to add all that heat to a 16-oz bottle of water, we could expect the temperature to increase by 1°F.

The much more commonly used term calorie is defined as the energy needed to raise the temperature of a gram of water one degree Celsius. One calorie is equal to 0.004 Btu, so it is quite a small measure of energy. The kind of measure I have in mind when thinking about my Thanksgiving meal is one Calorie (C) or 1000 calories (c). So one Calorie is equal to roughly four kitchen matches.

With these equivalencies in mind, I have a much better idea of why my energy intake is out of balance with energy expenditure. The ice cream alone that I added to my apple pie was 200°C or 800 kitchen matches worth of energy. Wow! When I do work up a sweat, the heat I’m giving off—some of those 800 kitchen matches—is obvious, but clearly it will take some exercise to burn up all that energy. In the meantime, my body stores the excess as fat, supposedly for later use.

Just as we can look up the caloric value for the foods we eat, we can also find detailed charts showing us how much energy we expend in various activities. In the end the goal is to balance the two. If you want to learn more about caloric balance in all kinds of animals, especially humans, I recommend you read Bernd Heinrich’s Why We Run. With that in mind, I think I’ll take a long walk to think about what we’ll discuss next week!

Thinking Thermally,

John Snell—The Snell Group, a Fluke Thermal Imaging Blog content partner

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