Overweight is one of Fallout GURPS disadvantages. See: Fallout GURPS.
You are unusually obese for your race. Overweight: Determine weight normally for ST, and then increase it by 30%. Being overweight carries a reaction penalty of -1 among health-conscious societies and in areas where food is in especially short supply”— Steve Jackson Games GURPS sources
With the abandonment of GURPS, Overweight was removed from the game