This is the explaination my research gave me:
The problem with taking glucomannan as a capsule is that the powder does not actually get released completely in order to expand in your stomach. Instead, gastric juices and acids break down the capsule walls slowly, and fluid from your stomach seeps in little by little.
As the fluid comes into contact with the glucomannan, it causes the fiber to swell inside the capsule, which is still partially intact. Since the fiber forms a thick gel when mixed with water, the partially encapsulated fiber becomes a glucomannan "fiber worm." Now, this isn't a parasite, it's simply the result of the expansion of glucomannan within the capsule to form a long, thin, worm-shaped gel. So, instead of swelling in your stomach to make you feel full, the fiber swells inside the capsule and passes through your digestive tract without performing its designated job.