Store that sells protein powder

GNC

This retail chain is known for its wide selection of health and wellness supplements.

The clue "Store that sells protein powder" points to GNC, a well-known retail chain specializing in health and nutrition supplements. GNC is a common abbreviation for General Nutrition Centers, which prominently sells protein powders and other fitness-related products. The answer relies on recognizing the brand's association with supplements rather than any wordplay or hidden meaning.