There isn't a specific 'most common eating disorder', but most people would have a disorder known as binge eating disorder, which is eating more than necessary. The other top 2 include anorexia nervosa or bulimia nervosa.
There are so many examples for that in different areas, like TPBi experiment carried out in our lab recently.Here's one link: http://www.alfa-chemistry.com/tpbi-cas-192198-85-9-item-282866.htm
The four polysaccharides are glycogen, starch, cellulose, and chitlin. You consume them. They are sometimes artificially made or produced by your body.