Metabolic response to a ketogenic breakfast in the healthy elderly

To determine whether the metabolism of glucose or ketones differs in the healthy elderly compared to young or middle-aged adults during mild, short-term ketosis induced by a ketogenic breakfast. Healthy subjects in three age groups (23 +/- 1, 50 +/- 1 and 76 +/- 2 y old) were given a ketogenic meal and plasma -hydroxybutyrate, glucose, insulin, triacylglycerols, total cholesterol, non-esterified fatty acids and breath acetone were measured over the subsequent 6 h. Each subject completed the protocol twice in order to determine the oxidation of a tracer dose of both carbon-13 (C-13) glucose and C-13- -hydroxybutyrate. The tracers were given separately in random order. Apolipoprotein E genotype was also determined in all subjects. Plasma glucose decreased and -hydroxybutyrate, acetone and insulin increased similarly over 6 h in all three groups after the ketogenic meal. There was no significant change in cholesterol, triacylglycerols or non-esterified fatty acids over the 6 h. C-13-glucose and C-13- -hydroxybutyrate oxidation peaked at 2-3 h post-dose for all age groups. Cumulative C-13-glucose oxidation over 24 h was significantly higher in the elderly but only versus the middle-aged group. There was no difference in cumulative 13C- -hydroxybutyrate oxidation between the three groups. Apolipoprotein E ( 4) was associated with elevated fasting cholesterol but was unrelated to the other plasma metabolites. Elderly people in relatively good health have a similar capacity to produce ketones and to oxidize C-13- -hydroxybutyrate as middle-aged or young adults, but oxidize C-13-glucose a little more rapidly than healthy middle-aged adults.