Relationship between plasma and erythrocyte magnesium and potassium concentrations in fasting obese subjects.

During 18-day fasts undertaken by 19 changed in all patients. Erythrocyte potasobese patients, plasma magnesium consium concentrations decreased by between centrations decreased in those given no 5% and 9% in those patients who had a mineral supplements or given calcium or decreased plasma magnesium concentrasodium supplements, but did not decrease tion, but did not change in the patients in those given magnesium supplements. who were given magnesium supplements. The extent of the decreases ranged from These findings indicate a possible effect of 9% in the nonsupplemented group to 25% extracellular magnesium concentration, or in the sodium-supplemented group. Plasma of some other correlate of magnesium potassium concentrations decreased more supplementation, on potassium distribution gradually in all patients, irrespective of and transport between extraand intramagnesium supplementation. Erythrocyte cellular compartments. magnesium concentrations remained un-