Family Dollar Stores Inc.'s fiscal second-quarter net income surged 33% on strong sales of food and cleaning supplies, prompting the discount retailer to raise its fiscal-year outlook.

Discounters have largely benefited in recent months from the economic downturn as shoppers turn to lower-cost outlets. Family Dollar's strategy, focused on value and convenience, continues to boost its store traffic and market share, according to Chief Executive Howard R. Levine.

Family...