Sodium acetate induces a metabolic alkalosis but not the increase in fatty acid oxidation observed following bicarbonate ingestion in humans

We conducted this study to quantify the oxidation of exogenous acetate and to determine the effect of increased acetate availability upon fat and carbohydrate utilization in humans at rest. Eight healthy volunteers (6 males and 2 females) completed 2 separate trials, 7 d apart in a single-blind, randomized, crossover design. On each occasion, respiratory gas and arterialized venous blood samples were taken before and during 180 min following consumption of a drink containing either sodium acetate (NaAc) or NaHCO₃ at a dose of 2 mmol/kg body mass. Labeled [1,2-¹³C] NaAc was added to the NaAc drink to quantify acetate oxidation. Both sodium salts induced a mild metabolic alkalosis and increased energy expenditure (P < 0.05) to a similar magnitude. NaHCO₃ ingestion increased fat utilization from 587 ± 83 kJ/180 min to 693 ± 101 kJ/180 min (P = 0.01) with no change in carbohydrate utilization. Following ingestion of NaAc, the amount of fat and carbohydrate utilized did not differ from the preingestion values. However, oxidation of the exogenous acetate almost entirely (90%) replaced the additional fat that had been oxidized during the bicarbonate trial. We determined that 80.1 ± 2.3% of an exogenous source of acetate is oxidized in humans at rest. Whereas NaHCO₃ ingestion increased fat oxidation, a similar response did not occur following NaAc ingestion despite the fact both sodium salts induced a similar increase in energy expenditure and shift in acid-base balance.