ccotta, you might try it in a smaller pan, not a loaf pan but a cake pan, without the cereal. Another idea might be to substitute some almond and/or flax meal. The cereal in your original recipe adds bulk and the almond or flax meal could do that, too, although not to the same extent. The meal would add some carbs but divided up into the individual portions, it might not be too bad.

Have you ever used whey protein powder? Is that a possibility?