 In contrast, conversion of the hydrogen at the C5 site from the α → β configuration reflects anaerobic microbial activity, and can be understood through isotope labeling experiments on controlled microbe experiments metabolizing the steroid of interest.One study demonstrated that there are two reactions that can produce loss of the cholesterol double bond—(1) direct reduction of double bond or (2) production of ketone prior to reduction of double bond—resulting in distinct isomerization of the hydrogen at the C5 site.The 14 and 17α hydrogen sites are more stable and undergo changes to β configuration in much lower abundances than the 5 hydrogen site.