Answer to Question #174401 in Mechanical Engineering for Ivy Ann Miller

Question

Fermi Problem

If we could convert all the weight that dieters lose in the United States every year to

energy, how many gallons of gasoline would be its equivalent?

Answer 1

One kilocalorie (kcal) is 4.18 kJ of energy. Carbohydrates and protein come in at 4 kcal/gram, while fat registers 9 kcal/g. For comparison, coal ranges from 4–7 kcal/g, gasoline is 10 kcal/g, and natural gas is 13 kcal/g. So fat is pretty much like gasoline.

We could use a gallon of lard for our fuel. This is truly the closest thing we could get to eating a gallon of gasoline proper. But we’ll tone it down and explore more standard fare.