Enviga is a Nestea carbonated green-tea drink being jointly marketed by the Coca-Cola Company and Nestle Switzerland. According to  industry analysts, Enviga is intended to target younger, active-lifestyle consumers. According to Coca-Cola, Enviga burns 60 to 100 calories per three 12-oz.(330 ml) cans. However this applies to three cans, not one. The loss for just one can is about 20–33 calories.
So, their claim is: Enviga drink provides fewer food calories than the calories needed to digest them, hence the weight loss according to the arguable "negative calorie" diet.