No those are all synthetic strings. Natural Gut strings are just what they are called, the guts of animals.
Ifs its a Natural Gut like some of gosen strings.. it is made from Corn Starch. Its biodegradable. Its like those green colored toothpicks.
Really, I didn't know Gosen made strings like that. What ever happened to truth in advertising? Oh well I guess they can say corn starch does appear in nature.