C13 NMR spectroscopy of lipids: a simple method for absolute quantitation.

There is both epidemiological and experimental evidence of the effect of fatty acid molecular structure, particularly the degree of saturation in fatty acyl chains, on the growth and regulation of certain tumours. In vivo carbon nuclear magnetic resonance spectroscopy has previously been shown to offer a non invasive technique for the evaluation of proportions of monounsaturated, polyunsaturated and saturated fatty acids in human adipose tissue. We present a simple method, which uses both endogenous water and fat as reference, to quantify in molar terms these lipid sub-categories for tissues other than pure fat. This could provide additional information in the debate on the protective effect in cancer of high polyunsaturated fatty acid (PUFA) diet. The method was validated by characterization of a lipid emulsion of known composition in various experimental set-ups and was applied to measure the lipid composition of the calves of two volunteers. Limitations and perspectives of the method are discussed.