[Relationship between nitrogen balance and amino acids, free fatty acids, glucose and insulin in human blood under various metabolic conditions (author's transl)].

Nutrition experiments with various levels of calorie and protein intake were carried out on five healthy young men. Three series of experiments with two persons each were undertaken for periods up to 14 days. The first part of each experiment, with 1100 to 1500 kcal/day, was immediately followed by the second part, with 3500 to 2300 kcal/day. The concentrations of insulin, free fatty acids, glucose and amino acids were determined in the morning, fasted blood. The nitrogen balance was also determined. When insufficient carbohydrate intake is coupled with normal and high protein content of the food, there is interindividually an initial drop in the insulin concentration. Regardless of the absolute insulin concentration, this drop causes an increase in the free fatty acids and the branched-chain amino acids, together with a decrease in the concentrations of alanine and glycine (threonine) in the blood and a negative nitrogen balance. The high concentrations of branched-chain amino acids and the low threonine concentrations might be involved as feedback regulators in the further regulation of the gluconeogenic metabolism. When carbohydrate calories are added to the diet, a simultaneous decrease in the free fatty acids and branched-chain amino acids and increase in the blood concentrations of insulin, alanine, glycine and threonine within 24 to 48 h are only observed with 3500 kcal/day and 0.8 to 1.4 g protein per kg body weight. A positive nitrogen balance, however, is only observed with 1.4 g protein per kg body weight, regardless of the relative changes in the insulin level, while the increase in alanine and decrease in branched-chain amino acids (valine) are greatest at 0.8 g protein per kg body weight and day. In spite of the high glucose level, the falling insulin level provokes counter-regulatory processes in which the low concentrations of branched-chain amino acids and the high threonine (alanine) concentrations may play a role.