EFFECTS OF BICARBONATE SUPPLEMENTATION ON URINARY MINERAL EXCRETION DURING VERY LOW-ENERGY DIETS

Metabolic acidosis is associated with increased calciuria and ammoniagenesis. This study evaluated the effects of oral sodium bicarbonate (NaHCO3) or combined potassium bicarbonate-calcium carbonate supplementation on urinary mineral excretion during the ketoacidosis of a very-low-energy protein diet. Seventeen healthy obese subjects (BMI: 37.5 +/- 3.2 kg/m2, weight: 100 +/- 3 kg) were given a 1.72 MJ all protein (93 g) liquid formula and a multivitamin-mineral supplement daily for 3 weeks. Subjects in groups 1 (n = 6) and 2 (n = 5) received 16 mmol KCl. In addition, subjects in group 1 received 60 mmol Na+ daily as sodium chloride, subjects in group 2, 60 mmol Na+- as NaHCO3. The subjects in group 3 (n = 6) were given 32 mmol K+ as bicarbonate and 16 mmol Ca++ as carbonate daily. Metabolic acidosis was prevented in groups 2 and 3 with bicarbonate and bicarbonate-carbonate administration. This was reflected in significant curtailment of the augmented ammonium nitrogen excretion found in group 1. The additional oral K+ in group 3 improved K+ balance and probably also inhibited ammoniagenesis. Urine calcium was greater (p < 0.04) in group 1 subjects, but similar in groups 2 and 3, despite higher calcium intake in group 3. Urinary phosphorus decreased with time in all groups, but more so in the group 2 subjects who received NaHCO3. Acidosis was associated with the reverse effect on urinary magnesium, which decreased in group 1 subjects. Thus adding the potassium bicarbonate-calcium carbonate preparation to a very low energy ketogenic diet spared both nitrogen and calcium in a manner similar to added NaHCO3, but also maintained better K+ balance.