As consumers pay greater attention to nutrition content when choosing food, voluntary front-of-pack labels have become popular tools for food marketers. However, voluntary nutrition labels provide certain freedoms regarding the disclosed information, which can be exploited. A common strategy is to disclose nutrition values based on smaller recommended serving sizes, which presents the nutrition amounts favorably on the label. Problematically, consumers can misinterpret such information and draw biased conclusions regarding product healthiness. This study uses purchase data with 61 products from both healthy (yogurt) and unhealthy (cookies) categories to analyze how recommended serving sizes on nutrition labels affect food sales. In line with our predictions, sales increased after a label introduction in the healthy (but not in the unhealthy) category for products with smaller recommended serving sizes. Since the least healthy versions within the category tend to have smaller recommended serving sizes, nutrition labels can stimulate sales of unhealthier food.