Fiber speeds passage of food through the gut, which results in less digestion time, which results in less digestion. Plus, as has been said, seeds have phytic acid, which leaches nutrients out of your system. SO yes, they will reduce absorption of nutrients. I would not take fiber as long as I was not getting backed up, and even then, I would only do it for a short time to alleviate the problem but then would taper off. WHne I first went lowcarb, I noticed my digestion was a bit slow for a while, but then my body adapted and now I intake very very little fiber and yet have no problems whatsoever with gut health or motility. In fact, it's probably healthier than it has ever been in my life.
That whole thing about fiber being so important was never backed by good evidence in the first place. It was just an excuse that tried to explain why natural tribes are healthier than Americans. The story was since scientists had already (incorrectly) decided that it could not be the sunshine, meat, and saturated fat that was so good for them, that it must be that fiber is soley responsible for their health! But there was never evidence to back that up and no research since then has provided any further evidence. The real question is where is the evidence that fiber is good for you? There never was any, and that is why fiber is starting to lose it's cache and new health fads are taking its place. My advice, dont worry about eating fiber. There is no long term advantage to scratching up the interior of your gut lining.