FAO scientists decided to measure people’s energy expenditures using the simplest metric possible, the physical activity level, or PAL.20 Your PAL is calculated as the ratio of how much energy you spend in a twenty-four-hour period divided by the amount of energy you would use to sustain your body if you never left your bed. This ratio has the advantage of being unbiased by differences in body size. Theoretically, a big person who is very physically active will have the same PAL as a small person who does the same activities.
