Glycerol turnover and oxidation in man

The oxidation and turnover of plasma glycerol has been studied in lean and obese, fed and starving man by means of a long-term infusion of glycerol-(14)C, and the participation of glycerol in gluconeogenesis has been determined. Under none of the experimental conditions did glycerol contribute more than 10% of the total respiratory CO(2). Glycerol turnover in fed lean subjects was 106 mmoles/min. Glycerol levels and turnover were higher in the obese subjects and with all subjects after starvation. There was a direct correlation between plasma levels and turnover values for which a regression equation was derived: y = 1556 x + 33.1, when y = turnover in micromoles per minute and x = glycerol level in micromoles per milliliter. Whereas a direct relation was established between glycerol and FFA levels, the FFA/glycerol turnover ratio was 4.7:1 in the lean group indicating incomplete hydrolysis of adipose tissue triglycerides.During starvation plasma glycerol is nearly or completely converted to glucose in the lean and obese groups, respectively. Of the new glucose formed from protein and glycerol 38% is derived from glycerol in the lean and 79% in the obese. Protein and glycerol have been shown to be adequate as precursors to supply at least as much glucose as is being oxidized per day.