What is the gas mileage of your body?

on Friday, January 28, 2011

Calories are a measure of energy stored in the food we eat. It can also be used to measure the stored energy in other fuels, like gasoline. Our bodies use fuel in the same basic way as an automobile. It is burned and the by-products of combustion are released as water vapor and carbon dioxide from our lungs or the tail pipe. This is why cars can run on corn oil, or alcohol (a bottle of vodka is 40% ethanol, which is used as a gasoline replacement in Iowa).

A gallon of gasoline is equivalent to about 28,972 calories. Each month, the average American uses 83,250 calories consumed as food; she "burns" 2.87 gallons of food-equivalent gasoline sitting around her house, watching TV, and vegetating in her cubicle, happily spewing the world-ending by-products of her internal combustion of whole grain rice, granola, and organic fair trade coffee.

So, back to our original question. How much extra C02 do you expel as you tool around town on your bike, or on your stationary bike at home? People don't often think of a bicycle in this way, but let me assure you, the C02 released from your lungs is exactly the same as the stuff coming out the back of your car.

A 190 lb person riding 16 mph burns 1,035 calories per hour. After an hour of riding that bicyclist burns 3.4% of a gallon of gas. He could ride 30 hours on one gallon of "food gasoline," which is equivalent to about 480 mpg. Moving without the bike is another story. The same guy running an eight minute mile (7.5 mph) nets only about 215 mpg. Modified Prius' currently get 100+ miles to the gallon, and they weigh 2,800 lbs! The Prius easily beats a human being in terms of pollution per pound.

Walking increases the gas mileage. A 190 lb person walking at three MPH would get 308 miles to the gallon; and smaller people get better gas mileage. A 130 lb person running the same mile would get 315 miles to the gallon. So why isn't anyone worried about exercise as a pollutant? Should we not recommend people move as little as possible to avoid a global catastrophe? Further, these calculations don't include exhaust from the human body; methane gas (farts) is 26-30 times more powerful a green house gas compared to CO2, and the average person "passes methane" 14 times per day.  Humans generate about relatively high amounts of pollution per unit of work performed.  To save the planet from greenhouse gases, we should be encouraging machines and gasoline to do everything they possibly can!

Depending on what you eat, it may actually cost less to drive to the store. If you were to live on Amy's frozen meals, which I have been known to do from time to time (Organic, $5 per box, really tasty, $15 per 1,000 calories) you would spend $30 in fuel to jog round trip to a store 7.5 miles away. If you take your regular old unmodified Prius it will cost you 59 cents in fuel (51 MPG in town, 29.4% of a gallon at $2 per gallon). It would cost $1.15 to get there and back in an SUV getting 13 MPG. (Running to the store living on Bic Macs is half price.)

This line of reasoning has other implications.  It implies that local gardening and backyard "farming," are much more hazardous to the environment (if you consider CO2 a pollutant).  Manufacturing food is not a CO2-free process, just as manufacturing roads and cars is not CO2-free. As we do work, running, exercising, gardening or farming, we are burning fuels that exhaust CO2 into the atmosphere, just like machines. Currently, we are not as efficient as a Prius in moving pounds from one place to another. If a Prius can move 2800 pounds with nearly the same CO2 exhaust as a human being moving 200 lbs, surely farm equipment can produce more food with less pollution than a human farmer.

A very CO2 and methane intensive activity
If you would like to counter by insisting that shipping foods 1,000 miles is burning additional fuel and creating hidden pollution greater than a might be generated by a home-farmer, let's think about why the food is shipped in the first place.  Why would we ship something in if it were cheaper (more efficient) to produce it locally? Perhaps we ship things in that we could make locally because it is cheaper to have machines mass-produce and mass-transport than to have smaller stations in each town duplicating efforts. Surely once upon a time we all farmed and someone said "hey, I'll farm all the tomatoes, you make all the lettuce, and we'll share!" Today we simply have more sharing; worldwide sharing that is more efficient and yields more food for less effort for everyone on earth. If a car can move weight from one place to another hundreds of times more efficiently (in terms of CO2 pollution) than a human "machine," why do we assume that a machine specifically designed to plant and harvest food can't farm hundreds of times more food per pound of CO2 released?