The metabolic response to two very low energy diets (VLED) of differing amino acid composition during weight reduction.

Nitrogen (N) sparing and even equilibrium have been achieved in obese subjects with all-protein weight-reducing very low energy diets (VLED) apparently independently of the content of essential amino acids. This study assessed whether the metabolic response observed at week 3 of an all-protein VLED with 46% of amino acids (aa) as essential was modified during week 4, when consuming a protein source that provided 16% of amino acids as essential. Six healthy obese subjects (BMI: 35.3 +/- 1.3 kg/m2, weight 90 +/- 9 kg) were given a 1.72 MJ (400 kcal) all protein (93 g) VLED and a multi-vitamin-mineral supplement daily for four weeks. During weeks 1 to 3, the protein was casein-soy (46% essential aa) and during week 4, tryptophan- and methionine-supplemented collagen hydrolysate (16% essential aa). At week 3, decreases in plasma glucose, insulin, cholesterol, blood pH and bicarbonate, and increases in plasma free fatty acids, serum urea, uric acid and blood and urine ketones occurred compared to baseline. These adaptations were unchanged at week 4. N balance returned toward equilibrium by day 23 remaining at values close to 0 despite the change in diet composition. Mean negative N balance did not differ between weeks 3 and 4 (-1.1 +/- 0.5 g vs. -0.6 +/- 0.5 g/day) and neither did mean urinary ammonium N excretion (0.71 +/- 0.08 vs. 0.73 +/- 0.07 g/day). Urinary urea N excretion tended to increase with the collagen-based diet reflecting the greater proportion of N in this protein source (18 vs. 15%).(ABSTRACT TRUNCATED AT 250 WORDS)