William T. Jarvis, former professor of public health, founder of the National Council against Health Fraud (www.ncahf.org):

“Enzymes are complex protein molecules produced by living organisms exclusively for their own use in promoting chemical reactions. Orally ingested enzymes are digested in the stomach and have no enzymatic activity in the eater.” 

Andrea Giancoli, R.D., a spokesperson for the American Dietetic Association:

“Enzymes are proteins and proteins denature with heat, but those enzymes are denatured - and thus inactivated - when they reach our stomachs. Our stomach acids are designed to break down proteins very efficiently.”