This site calls Berberine one of the most researched botanicals for glycemic control and says Gymnema has a long history in blood sugar research.
Berberine is framed as the lead glycemic-support ingredient; Gymnema Sylvestre as a traditional botanical tied to blood sugar and craving support. Together they are the two ingredients the site leans on for its research claims.
The blog's existing guides cover each botanical on its own. This pairing view is about how the two sit side by side in one formula, not a replacement for either guide.