The definition of 100% Complete is that the food contains all the nutritients essential for life.
The definition of Balanced is that the food contains the minimum quantities necessary of all essential nutrients.
Therefore a pet food can be labelled 100% Complete, but not be able to sustain life without the pet having to eat large quantities of it in order to obtain it's minimum requirements; leading the owner to believe that the pet enjoys the food and the pet towards obesity.
Patrick, J.S. (2006) Deconstructing the Regulatory Façade: Why Confused Consumers Feed their Pets Ring Dings and Krispy Kremes. [Internet] Available from: http://leda.law.harvard.edu/leda/data/784/Patrick06.html#fn77 (accessed 21/12/2011)