Although the word “bran” appears in the phrase “bran flakes” and actual bran is in the flakes, you won’t be able to substitute for real bran. Bran flakes is a processed food and contains other ingredients that will affect the final flavour and texture of your recipe.
Quick botany lesson: bran is the outer layer of a wheat or oat berry (which is a dry fruit containing a seed). Bran is removed from refined grains in the milling process. It’s full of good things like fibre and essential fatty acids, vitamins, minerals, protein and starch. Bran will improve gut health, promotes heart health, gives you a feeling of fullness to aid with weight loss, and may prevent certain cancers. All that, and a hearty texture and a sweet, nutty flavour for muffins, cookies, sprinkled over other cereals, or blended in a smoothie. Because of the oil content, bran can go rancid and should be stored in the refrigerator.
When a recipe asks for bran, they generally mean wheat bran, but you can also get oat bran — these aren’t interchangeable since they absorb moisture differently. Make sure you know which to use and stick with the recipe if you want predictable results. Quick breads — muffins and loaves — are sometimes more forgiving of substitutions of one kind of bran with another, but you may have to adjust quantities.