Hi, Suirsuss. I have the impression that although dietary fiber does absorb and eliminate fats, that you have to take allot of it to have a significant effect on general fat intake. For instance, this meta study finds little correlation between Chitosan supplementation and weight loss:
Chitosan for overweight or obesityThere is some evidence that chitosan is more effective than placebo in the short-term treatment of overweight and obesity. However, many trials to date have been of poor quality and results have been variable. Results obtained from high quality trials indicate that the effect of chitosan on body weight is minimal and unlikely to be of clinical significance.
My own take on fiber generally is that its lipid absorption effect is pretty localized and dependent on direct contact in the digestive tract and limited in the amount of fats it can absorb per gram of fiber. I just try not to take fiber supplements at the same time as oils and/or oil soluble supplements I value. But I might down a couple of chitosan caps before enjoying a fatty steak or juicy bratwurst in the hopes of minimizing the damage... which might be mostly wishful thinking.
Howard