Those who carry their weight well have the Brawny Edge. Those who don't are Obese. A character cannot be both Brawny and Obese, and this Hindrance can't increase your Size above +3.
An Obese hero's Size (and therefore Toughness) increase by +1. His Pace is reduced by 1, and his running die one die type (minimum d4). Strength is considered one die type less (minimum d4) for armor and worn gear (not weapons). They may also have difficulty finding armor or clothing that fits or entering confined spaces.