If the propoion of the dietary fiber / roughage is high in a diet, it will:-

If the roughage is high in diet, it will remain undigested, therefore, it will increase bulk of the stool & it will decrease transit time in the colon. It decreases the glycemic response to a carbohydrate meal. Because it does not allow the absorption of carbohydrates digestates & fat digestates (polysaccharides in fibers remain undigested). Roughage in diet prevents the fat absorption that is why it is advocated as weight loss type of meal and if it decreases the fat absorption then there will be less circulation of bile.