There is no fast method for fiber quantification as you must eliminate as specifically as possible starch and sugars, which are very close chemically to most fibers. You definitely can  NOT use carbohydrates as most fibers are carbohydrate in  nature. Elimination of starch in particular is very time-conuming and finicky as some starches actually can be classified as fibers. AOAC methods though far from perfect are the best you'll find.

Hi, Stefano

As Catherine explained there is no fast and easy method for estimation of Fibre, but you can use fiber plus equipment which need no assistant during the process. It's very easy, time saving and  can run 6 samples at a time and also you will get reliable accurate results.

Best of luck

No, you can't do it, as Catherine said fibers are carbohydrates in nature. Therefore, you need to hydrolyze firstly the majority of the starches except the resistant ones. In addition to time-consuming, the technique for dietary fiber is expensive.

Agreed with all above. Enzymatic steps are central to process. Also "dietary fiber" as recently re-difined now includes all amylase resistant species with DP equal to 3 and above. Most of these material precipitate with 80% alcohol. In principle you can determine alcohol insoluble material - after amylase/ glucosidase digestion steps. There is much to be said for using a dedicated assay kit.