In vivo fatty acid analysis in humans and animals using carbon-13 nuclear magnetic resonance spectroscopy

The signals observed in in vivo carbon-13 nuclear magnetic resonance (13C NMR) spectra are from ‘mobile’ molecules, i.e. those with relatively unrestricted motion. In practice, this eliminates virtually all 13C present in proteins and other macromolecules. Because of sensitivity limitations, mobile molecules present at low concentrations are also not detectable. As a result, 13C NMR mainly detects ‘mobile’ fatty acids, i.e. free fatty acids and triglycerides. Fatty acids in phospholipids are considered to be largely ’invisible’by 13C NMR. For measurements done in vivo, the main signal observed is from adipose tissue triglycerides because the trunk and limbs are surrounded by varying thicknesses of adipose tissue