The holiday season can be a time of excess, but low- or no-calorie sweeteners could help merry-makers stay trim. Stevia is a zero-calorie sweetener that is sometimes called “natural” because it is extracted from the leaves of a South American plant. Now, a report in ACS Synthetic Biology describes a way to prepare large quantities of stevia using yeast, which would cut out the plant middleman and could lead to a better tasting product.