You can add almost anything: ground nuts, cornmeal, oatmeal, chia seeds, etc. Each one will give your muffin a different taste and texture. read more
Another good substitute is buckwheat. Even flaxseed and ground sunflower seeds can be used to substitute oat bran in cookies and muffins. On the other hand, oat bran itself can be a good substitute for wheat bran. You can use ground oat bran and oats to substitute wheat flour as well. read more