The conversion of molecules from one form to another within an organism, often associated with change in pharmacological or the activities of drugs: Biotransformation simply means the changes of chemicals in the body; such as, nutrients, amino acids (carbon, hydrogen, oxygen, nitrogen) and toxins (poisons) all of which can be modified for good or bad conditions.

The anaerobic environment (absence of air) of the intestines promotes biotransformation of chemicals with bacteria.