When grain is refined, there are typically by-products and leftovers. There is a certain irony in the fact that these are often the best bits.
Wheatgerm is a tasty part of the centre of the seed. It is removed when making white flour, but kept into wholemeal flour. It is very nutritious, and in powdered form adds protein, flavour, vitamins, minerals and essential fatty acids to your muesli.
Oat bran a little less exciting, so is generally added to oatgerm to make it tasty. Oat bran is high in fibre (being the husk of oats), and together with the oatgerm adds flavour and texture to muesli. Oatgerm , like wheatgerm, is also high in protein.