Abstracts

A number of reports have found that low carbohydrate (e.g., Atkins) or low glycemic index diets may help in reducing seizure frequency. Given the relatively lower ketosis achieved in such diets as compared to the ketogenic diet, it is possible that the effect of seizure control is not via direct ketone (or ketone derivatives) levels in the brain, but through a physiological mechanism. We examined for such a mechanism by studying the effects of 4 weeks of an Atkins diet on cerebral energetics in n=7 healthy overweight control adult volunteers., We used high field 31P whole brain MRSI to study healthy overweight (n=7, mean age 34.7[plusmn]10.0years, 4F) volunteers, examining them prior to initiating a low carbohydrate diet (Atkins Phase 1) and after 4 weeks of sustaining this diet. For optimum diet control, meals from a licensed caterer were provided to the subjects, and the macronutrient distribution of the diet was 65% fat: 30% protein: 5% carbohydrate. The mean body mass index at baseline was 34.0[plusmn]2.7, and after 4 weeks of the diet was 31.2[plusmn]2.2. Weight loss was achieved by all volunteers, averaging 6.7[plusmn]3.2kg.
31P MRSI was performed at 4Tesla. Including scout imaging and calibrations, the duration of the 31P study was [sim]75min. The 31P acquisition has an effective sampling radius of 1.4cm; previous studies have shown the reproducibility to be 10%. Quantification was performed accounting for tissue volume, coil loading and relaxation.
Plasma samples were frozen at [ndash]80C until analysis; b-hydroxybutyrate concentrations were spectrophotometrically assayed after each study using a COBAS-FARA analyzer., A mild ketosis was achieved in all subjects, with plasma BHB rising from 0.24[plusmn]0.05 to 1.64[plusmn]0.93. Example data (position and spectra) are shown in Fig. 1, showing PCr, ATP and inorganic phosphate Pi. Data and loci of spectral analysis are shown in the Table. From all volunteers, the ATP and PCr concentrations in the hippocampus and thalamus rose significantly between D0 to D28, while there was no significant change in occipital cortical tissue., Cerebral energetics changed with use of a low carbohydrate diet, with increased ATP and PCr concentrations in the thalamus and hippocampus. The data are consistent with a view that the change in fuel type and availability is characterized by an alteration in energetics particularly in subcortical brain structures. The increased availability of high energy phosphates in key limbic structures may be an important factor in how a low carbohydrate diet affects seizure control.[figure1], (Supported by NIH R01NS40550.)