Most natural flavors are safely gluten-free, but use caution. The term “natural flavors” on a product that is not labeled or certified gluten-free means it could be made using a gluten-containing ingredient such as yeast extract that was grown on barley. Unless you can confirm the natural flavor does not contain yeast extract, it should be avoided. The GFCO program confirms that every natural flavor used in certified products does not contain yeast extract grown on barley (or other gluten sources), so one way to be sure is to look for GFCO certified products.  If a natural flavor in an FDA-regulated product contains wheat, it must be stated on the label.