Intestinal flora (bacteria) digests all EXCEPT:

Ans. (b) Lignin* The gut floras primary benefit to the host is the gleaning of energy from the fermentation of undigested carbohydrates and the subsequent absorption of short chain fatty acids. They can even digest even products like cellulose, pectin, and starch.* The most important of these are butyrates, metabolized by the colonic epithelium; propionates by the liver; and acetates by the muscle tissue.* Intestinal bacteria also play a role in synthesizing vitamin B and vitamin K as well as metabolizing bile acids, sterols, and xenobiotics.* The human body carries about 100 trillion microorganisms in its intestines, a number ten times greater than the total number of human cells in the body* Lignin or lignen is a complex polymer of aromatic alcohols known as monolignols. It is most commonly derived from wood and is an integral part of the secondary cell walls of plants.