It is a white, free-flowing powder. Chemically, it is an inert substance, is not degraded during digestion and has no appreciable absorption.
Microcrystalline Cellulose is not absorbed into the blood stream or stomach.
Microcrystalline cellulose is a commonly used excipient in the pharmaceutical industry. It has excellent compressibility properties and is used in solid dose forms, such as tablets. Tablets can be formed that are hard, but dissolve quickly. Microcrystalline cellulose is the same as cellulose, except that it meets pharmaceutical standards.
It is also found in many processed food products, and may be used as an anti-caking agent, stabilizer, texture modifier, or suspending agent among other uses. According to the Select Committee on GRAS Substances, microcrystalline cellulose is generally regarded as safe when used in normal quantities.
Cellulose is a non-digestible plant fiber, and we actually happen to need non-digestible vegetable fiber in our food—that's why people eat bran flakes and psyllium husks.
We've already been eating a lot it, for a long time.
Cellulose is a popular additive to food products is that it adds body and mimics the characteristics of more luxurious foods without adding calories or fat.
"It has certain physical properties that allow manufacturers to cut out other ingredients to make everything from toothpaste to pancake syrup or low-fat cookies or low-fat ice-creams that have the mouthfeel of ice-creams with regular levels of fat.
Cellulose is prized for its inherent dryness. That property allows it absorb moisture in certain kinds of foods, like baked goods, and thus reduce spoilage. In other cases, it makes for a less "slimy" texture than you might get with other common additives like agar or pectin.
So cellulose is completely safe to eat.