No, bananas are not high in yeast. Yeast is a type of fungus, and it is not a component of bananas. However, bananas can provide a suitable environment for yeast growth if they are overripe and begin to ferment, as the natural sugars in the fruit can promote the growth of yeast and other microorganisms. This is why bananas can be used as a natural leavening agent in baking, as the yeast in the mixture feeds on the natural sugars in the fruit and produces carbon dioxide, which helps the dough rise. But in general, bananas themselves are not high in yeast.