What's oat bran? It's the outer shell of the oat that gets removed during processing.
One of the benefits of eating oat bran is that it reduces cholesterol. It also helps digestion. What's more, it's one of the main sources of fiber during the attack and cruise phases of the diet.
Dukan requires you to take increasing amounts as the diet progresses.
Attack Phase - 1.5Tbs
Cruise Phase - 2Tbs
Consolidation Phase (and onward) - 3Tbs
I find it really fills you up and allows you a chance to eat something a bit like carbs. The easiest way to eat it is to put it in yogurt, but I've also made pancakes with it (using fat-free yogurt and eggs) as well as actually baking muffins with it (same as the pancakes, but add baking powder and spices, etc. It turns out quite well and goes pretty well with meat, etc.
We found ours quite cheap here in Japan, so I'm assuming in places like the US and UK, you can find it even easier. Whether or not you do the Dukan diet, it wouldn't be a bad idea to add a bit of oat bran to your diet.