Effects of sodium bicarbonate on nitrogen metabolism and ketone bodies during very low energy protein diets in obese subjects

Abstract

This study evaluated the effects of oral sodium bicarbonate (NaHCO 3) supplementation on ammonium (NH 4 +) nitrogen (N) and urea N excretion and on ketone bodies during the metabolic acidosis of a very low energy protein diet. Ten healthy obese female subjects (BMI, 38.4 ± 1.5 kg/m 2; weight, 100 ± 4 kg) were given a 1.72 MJ (412 kcal) all protein (16.8 g N) liquid formula, 16 mmol KCl and a multivitamin-mineral supplement daily for 4 weeks. In addition, the five subjects in group 1 received 60 mmol Na + daily as sodium chloride (NaCl) for 3 weeks and as NaHCO 3 during week 4. The subjects in group 2 were given 40 mmol/d NaHCO 3 during the first week, 60 mmol/d during weeks 2 and 3, and 60 mmol/d NaCl during week 4. Nitrogen balance was achieved in both groups by the end of week 3. The subjects in group 1 at week 2 showed an increase in blood [H +] of 0.41 ± 0.06 × 10 −8 mol/L and a decrease in blood bicarbonate from 26.0 ± 0.8 to 23.8 ± 1.2 mmol/L. The subsequent NaHCO 3 curtailed NH 4 + N excretion by one half, without significant change in ketone body levels or excretion. Administration of NaHCO 3 from the start of the diet to the subjects in group 2 prevented both the metabolic acidosis and the increase in NH 4 + N excretion and attenuated the increase in blood and urine 3-hydroxybutyrate. When NaCl replaced NaHCO 3 during week 4, ammonium N excretion doubled. Urea N excretion was comparable in both groups and was unaffected by bicarbonate. Thus, NaHCO 3 supplementation resulted in the sparing of 9.11 g of N in 3 weeks and in the lowering of ketone body levels and excretion, at least in part by the neutralizing effect of HCO 3 − on the diet-induced metabolic acidosis.