Tuesday, July 24, 2007

How many gallons do you have around your waist?

Human fat tissue contains about 87% lipids, so that 1 kg of body-fat tissue has roughly the caloric energy of 870 g of pure fat, or 7800 kcal. In principle one has to create a 7800 kcal deficit or surplus between energy intake and use to lose or gain 1 kg of body-fat. (or 3500 kcal per pound). However, if one eats 7800 kcal more than the body needs, one won't necessarily gain 1 kg of fat, since muscle and other tissues may be built. The same way, if one eats 7800 kcal less than their maintenance level, they may not lose 1 kg of fat, since muscle and sugars may be metabolized to generate energy.[1]


Okay, so let's see, 56 pounds to lose to get to 200 pounds. That's 25.4 kg of fatty tissue or 22.1 kg of pure fat.

22.1 kg * 7800 kcal/kg = 172,364.4 kcal

172,364.4 kcal * 4.184 kJ/kcal = 721,172.65 kJ or 721 MJ.

There is approximately 131 MJ of gas in a gallon of gas[2] or

721 MJ / 131 MJ/gal = 5.5 gal of gas around my gut, or about 150-200 miles with the Honda. I can certainly bike farther than that on the fat I've got.

[1] Wikipedia entry on Calorie - Trivia note #3
[2] Wikipedia entry on Gasoline - Energy content

3 comments:

The donut guy said...

I wonder how many donuts is in a pound of fat......

bother yam said...

According to Krispy Kreme, an original glazed donut has 200 Calories, 100 Calories from fat. 3500 Calories in a pound of human fat divided by 200 Calories per donut gives you about 17 and a half donuts.

Now you have different recipes, so I'm sure that these numbers differ but at least you have a baseline.

17.5 donuts is about 17 more donuts than I can eat. Not much for fried pastries. Bagels and cream cheese, on the other hand, is a completely different story...

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