Hi Claire! We think it would be OK to replace up to 1/2 cup of the flour with 1/2 cup of wheat germ, but a whole cup of wheat germ will likely make for a flatter loaf that is a bit denser than normally expected. The baking temperature won't need to be adjusted if the sunflower seeds are mixed into the batter but if you plan to use the seeds as a topping we'd suggest lowering the baking temperature to 375°F. Happy baking! 

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