"All-Natural" Pure Fiber Powder

Hello, I just signed up for this forum and I had a question which I trust the experts here will be able to answer.

I'm looking for a substitute for E461 Methylcellulose which is "naturally" derived. Therefore I'm seeking something along the lines of a flax lignan or other natural dietary fiber but which is in powder form and doesn't contain the oils, etc. which drive the caloric value up. It doesn't have to be from flax as it could be derived from any grain, nut, vegetable peel, etc. The key is that the caloric value be very low or even close to zero as in the case of E461. It is not important that it be soluble, only that it is GRAS.

Any assistance would be appreciated!

Have you tried looking into Beta Glucan? its an oat derived natural soluble fiber. 

Thanks for your reply, but beta glucan's caloric value is approx. 350kcal/100g so it's effectively identical to any other carbohydrate. I have to apply something that has a caloric value of zero or close to it, similar to E461. It has to be essentially pure but undigestible fiber.