Some dietary fibers protect against,while others have no effect or even promote colon cancer.Among the dietary fibers,wheat bran was consistently reported to protect against colon cancer.The mechanism of action of wheat bran dietary fiber was investigated by studying the characteristics of fermented residue and comparing the results with those of sugarcane bagasse.The residues were made by fermenting wheat bran or sugarcane bagasse using human colon microflora.The shape,size distribution and zeta potential of micro-particles from fermented residues were studied by atomic force microscopy,laser light scattering,and electrokinetic measurements respectively.