| Metamucil is a brand name for processed dietary fiber made by Proctor & Gamble. The fiber in the various types of Metamucil is wheat psyllium, which is the same substance in flour that makes bread stick together as it rises.
Even though you may laugh at Metamucil because you associate it with your grandparents, it is actually quite good for you.
For one thing, eating a good amount of fiber in your daily diet prevents residoo, which is the substance that you have to remove from your butt with toilet paper after you poop. This result of taking Metamucil daily is known as residon't. It is a good thing.
Second, a diet high in fiber can actually reduce your blood cholesterol level, particularly the bad LDL kind. Fiber has also been shown to reduce the risk of colon cancer. Believe me, if you have ever had to prepare for a colonoscopy, you know this is not a fun thing.
The trick to ingesting Metamucil without barfing is to mix it with a lot of water, and drink it quickly. It tastes a lot like Tang, if you are old enough to remember that powdered drink. This also helps you stay hydrated.
Whipster's pet name for Metamucil is MetaMuck. | 
