What do calories measure? Energy! Doesn't (directly) matter if it is energy to feed a car or feed your soul; we can use calories for both. In 1940 the average farm in the U.S. produced 2.3 calories of food energy for every calorie of fossil energy it used. By 1974 that ratio was 1:1(1). Today that ratio is on average 10 calories of fossil energy for every one calorie of food(2).
This means that for a USDA recommended 2500 calorie daily diet there are 25,000 calories of fossil fuel (dead Dinos) embedded in one day's food. So how many is this for a year?
Kids, how much does 25,000 times 365 equal? Anyone?
A Really Big Number: 9,125,000 calories.
Whoa. So how much gas does this Really Big Number represent? Go Googling, Mr(s). Detective, and you should find that there are 31,000 calories in one gallon of gas. Go on a tangent (as usually happens when cruising the web) and you will find that a gallon of gas also includes almost 20 pounds of carbon (19.4 to be exact, but for this post let's keep the math simple).
(Wait. 20 pounds of carbon? In a gallon of gas? A gallon only weighs like 6 pounds. How can that be?)
So go grab your calculators and try to calculate how much gas and carbon is in a year's worth of food.
So you may ask, what does this have to do with the price of bread? Well, alot. And it involves not just the bread we eat, it involves the air we breath and the climate we are a 'changing.
For one person:
A year of recommended calories (2,500 per day)
contains 9,125,000 calories of energy (for conventional industrialized food)
that equals 294 gallons of gas in every person's food
and 5,884 pounds of carbon entering the atmosphere.
That's per person. In the U.S. we now have 300 million people. Let's just take 1% of that number, 3 million people, which happens to be about the population of a large metropolitan area like Seattle.
This means each year 3 million people eat food containing the equivalent of 88.2 billion gallons of gas and 882 million tons of carbon that has entered our atmosphere.
Pass the local organic salad, please.
(1): Richard Manning, "The Oil We Eat: Following the food chain back to Iraq," Harper's Magazine, Friday, July 23, 2004
(2): see Food System Factoids Post "So how much energy do we use to make ... energy?"