With a hand-held mixer, beat the egg whites in a medium bowl, until frothy. While still beating, slowly add the sugar and beat on high speed until the egg whites are stiff and shiny, about 4 minutes. (This can also be done in the bowl of an electric mixer fitted with the whisk attachment).
In another bowl, whisk the yogurt until smooth. Fold in the egg whites. Transfer the mixture to an ice cream freezer and freeze according to the manufacturer's instructions. Freeze in a quart container until ready to serve.
Consumption of raw or undercooked eggs, shellfish and meat may increase the risk of foodborne illness.