I think you could say the same of sweetcorn, as for tigers, because if you examine your stools after eating sweet corn, it's often often evident that corn is almost completely intact, yet it's universally accepted that sweetcorn is good for us. Also the fine flour or meal of tigers, may be coming out in a similar state it went in, but as the particles are finer, they're probably not as identifiable when they come out the other end, but if tiger nut flour is part of a boilie, alongside other ingredients used together they create a more valuable and complete food source, and are then suitable for consumption in larger quantities. So in the right amounts, i think insoluble plant fibres can be very good for both humans and fish, because your microbiome, (the colony of beneficial bacteria in your gut), feed on them, and with there being more bacteria organisms in the human gut, than there are people on the planet, the importance of the fibre that help maintain this colony of bacteria, which is something nutritional science is realising the importance of now more than ever, the same or similar is likely to be true of carp and many other animal species, though the exact species of bacteria in a fish's gut are probably slightly different to those in humans, but some or many of the strains will surely be similar to those found in humans imo. If as humans we were to eat nothing but the kind of fibre in tiger nuts though, then we would eventually become quite thin, and malnourished, so it is right to use tigers sparingly, or as part of a more complete boilie food source. This is also one of the reasons i think the unnatural vegan plant based diets being promoted at the moment aren't as healthy as some people think, but that's another story, In short in the right quantities fibre can be very healthy and an important part of both our, and the carp's diet, but as stated, i think fibre shouldn't be consumed in huge quantities all the time, i also think there will be times of year fibre is required more by the carp, like spring, because fibre also has detoxing qualities, that may help fish get rid of some of the parasites acquired through their winter torpor.