Protein wasting due to acidosis of prolonged fasting

Publisher Website
Google Scholar
Abstract
During a total fast in obese subjects, the daily rate of N excretion undergoes only a small further decline after 2 wk, the excretion rate being .apprx. 5 g N/day. At this time, NH4 and urea each constitute .apprx. 1/2 of this excretion. The purpose of this study was to consider 2 alternative hypotheses: 1st, that the near plateau in N excretion represents an irreducible minimum rate of net protein breakdown in order to supply essential organs with calories in the form of glucose; 2nd, that protein breakdown could be further reduced by minimizing the requirement to provide N for NH4 excretion during the ketoacidosis of fasting. Because NH4 excretion is largely controlled by acid-base balance 150 mmol of sodium bicarbonate plus 60 mmol of KCl were administered daily to decrease NH4 excretion in 8 obese subjects who were totally fasting for > 14 days. Urine ammonium nitrogen excretion fell with this treatment (from 3.8 .+-. 0.4 to 2.0 .+-. 0.4 g N/g creatinine). In addition, there was a smaller fall in the rate of urea excretion (from 2.5 .+-. 0.2 to 2.1 .+-. 0.3 g N/g creatinine) together with a fall in the blood urea N. NH4 excretion probably contributes to the negative N balance of a prolonged total fast and, as assessed over a 3-day period of observation, is responsible for .apprx. 1/3 of the net lean body mass loss.