6Ketosis of starvation: A revisit and new perspectives

During starvation ketone bodies, acetoacetate (AcAc), 3-hydroxybntyrate (fl-OHB) and acetone accumulate in the body fluids. AcAc and /3-OHB are synthesized in the liver primarily from the partial oxidation of long-chain fatty acids. They are released into the blood as short-chain fatty acids, dissociate to become water-soluble anions and are distributed at different concentrations in the water components of the body (Owen et al, 1973). Acetone is probably formed by spontaneous decarboxylation of AcAc. Acetone is a neutral compound, and, unlike AcAc and/3-OHB, it does not affect blood bicarbonate concentration, arterial blood gases or pH (Sulway and Malins, 1970). Acetone is soluble in both water and lipids, and therefore it is distributed throughout the body (Reichard et al, 1979). During food deprivation, starvation ketosis is arbitrarily defined as being present when the minimum blood/plasma concentration of AcAc is about 1.0 mmol/1. Concurrent concentrations of/3-OHB and acetone are usually about 2.0 and 0.5 mmol/1, respectively. Such values are usually present after 2- 3 days of total starvation. Maximal blood/plasma concentrations of AcAc (2- 4 mmol/1),/3-OHB (5 - 12 retool/l) and acetone (3 -5 mmol/l) develop after several weeks of total fasting. The arbitrary definition of starvation ketosis is centred on the plasma/serum AcAc concentration, because the only semiquantitative test preparations, widely available to detect the presence of ketone bodies in biological fluids, depend upon the reagent nitroprusside to react with AcAc. Contrary to popula~ opinion, the presence of acetone or/3-OHB does not augment nitroprusside reactivity with AcAc. Plasma/serum/urine concentrations of AcAc below 0.5 mmol/1 are nonreactive with commercially available diagnostic tests. However, these semiquantitative tests develop reactions that are roughly concentration dependent. Nitroprusside tests show 1 + (trace to small) reactivity with 1 -2 mmol AcAc, 2 + (small to moderate) reactivity with 3 -4 mmol AcAc and 3 + (moderate to large) reactivity with 5 - 10 mmol AcAc. Thus, high