The definition has one advantage, which is that researchers can get comparable information about poverty for any country in the world. The disadvantage is that it's arbitrary (why one third? why food? why not shelter, health care, and heating?); the other is that the cost of living varies dramatically in different neighborhoods in different cities of different US states, yet the poverty level is the same (expressed in dollar amounts) everywhere in a given country.
A better measure is the self-sufficiency standard.