In vivo C-13 nuclear magnetic resonance: Applications and current limitations for noninvasive assessment of fatty acid status

As a noninvasive method, in vivo C-13 nuclear magnetic resonance has potentially important applications in understanding the metabolism of long chain fatty acids in organs of living humans. At present, this methodology is most advanced for research on glucose utilization. However, the main C-13 signals visible in vivo are from fatty acids in adipose tissue and the olefinic signals can be used to noninvasively estimate adipose tissue content and relative dietary intake of polyunsaturates and monounsaturates. The low natural abundance of C-13 improves the utility of this isotope for fatty acid tracer studies. Due to excessive signal broadening, uniform C-13-labelling seems to have limited application in in vivo fatty acid studies. Tracer fatty acids with C-13 enrichment at a specific carbon position, i.e., [3-C-13]gamma-linolenate, appear to be the most useful for in vivo tracer studies. Development of methods permitting resolution of C-13 enrichment in structural lipids of lean tissues will be an important breakthrough which may make human tracer studies feasible and worthwhile.