Measurement of human lipogenesis using deuterium incorporation.

In order to determine human triglyceride fatty acid (TG-FA) synthesis rates, the incorporation of deuterium from the plasma water pool in vivo into TG-FA was measured over 48 h in six healthy males under steady state conditions. Subjects consumed a nutritionally complete liquid diet as six evenly spaced small meals per day for 3 days and drank 0.7 g D2O/kg estimated body water, (99.8 APE) at 0800 h on day 2. D2O was added to the liquid diets to maintain plasma deuterium enrichment at plateau over days 2 and 3. Blood samples were obtained prior to dosing and every 4 h thereafter. Total TG-FA were obtained from plasma at each timepoint and combusted. The resultant water was vacuum-distilled into Zn-containing Pyrex tubes, reduced to hydrogen gas, and analyzed for deuterium abundance by isotope ratio mass spectrometry. TG-FA deuterium enrichment reached a plateau at approximately 12 h post-dose. To establish the amount of newly synthesized TG-FA in the total plasma TG-FA pool, two models were developed relating the maximum observed deuterium enrichment to the calculated theoretical maximum enrichment. In model A, it was assumed that TG-FA come solely from chylomicrons. This yields a value of 8.8 +/- 4.6 g/day (mean +/- SD) de novo synthesized TG-FA. On the opposite extreme in model B, it was assumed that all the TG-FA are derived from recycled very low density lipoprotein (VLDL); the amount of newly synthesized TG-FA calculated by this model was 1.7 +/- 0.8 g/day.(ABSTRACT TRUNCATED AT 250 WORDS)