title: No protein intake compensation for insufficient indispensable amino acid intake with a low-protein diet for 12 days.
abstract: BACKGROUND
  Protein quality evaluation aims to determine the capacity of food sources and diets to meet protein and indispensable amino acid (IAA) requirements. This study determined whether nitrogen balance was affected and whether dietary IAA were adequately obtained from the ad libitum consumption of diets at three levels of protein from different primary sources for 12 days.
  
  
  METHODS
  Two 12-day randomized crossover design trials were conducted in healthy subjects [n = 70/67 (M/F); age: 19-70 y; BMI: 18.2-38.7 kg/m(2)]. The relative dietary protein content was lower than [5% of energy (En%)], similar to (15En%), and higher than (30En%) customary diets. These diets had a limited variety of protein sources, containing wheat protein as a single protein source (5En%-protein diet) or 5En% from wheat protein with 10En% (15En%-protein diets) or 25En% (30En%-protein diets) added from whey with α-lactalbumin, soy or beef protein.
  
  
  RESULTS
  There was a dose-dependent increase in nitrogen excretion with increasing dietary protein content, irrespective of the protein sources (P = 0.001). Nitrogen balance was maintained on the 5En%-protein diet, and was positive on the 15En%- and 30En%-protein diets (P < 0.001) over 12 days. Protein intake from the 5En%-protein diet did not reach the amount necessary to meet the calculated minimal IAA requirements, but IAA were sufficiently obtained from the 15En%- and 30En%-protein diets. In the 15En%- and 30En%-protein conditions, a higher protein intake from the soy-containing diets than from the whey with α-lactalbumin or beef containing diets was needed to meet the minimal IAA requirements.
  
  
  CONCLUSIONS
  Protein intake did not compensate for an insufficient indispensable amino acid intake with a low-protein diet for 12 days.
  
  
  BACKGROUND
  These trials were registered at clinicaltrials.gov as NCT01320189 and NCT01646749.
authors.affiliation: Department of Human Biology, Nutrition and Toxicology Research Institute Maastricht (NUTRIM), Maastricht University, PO Box 616, 6200, MD Maastricht, The Netherlands.
authors.forename: Eveline A
authors.initials: EA
authors.lastname: Martens
authors.affiliation: Department of Nutrition Science, Purdue University, West Lafayette, IN 47905, USA.
authors.forename: Sze-Yen
authors.initials: SY
authors.lastname: Tan
authors.affiliation: Department of Nutrition Science, Purdue University, West Lafayette, IN 47905, USA.
authors.forename: Richard D
authors.initials: RD
authors.lastname: Mattes
authors.affiliation: Department of Human Biology, Nutrition and Toxicology Research Institute Maastricht (NUTRIM), Maastricht University, PO Box 616, 6200, MD Maastricht, The Netherlands.
authors.forename: Margriet S
authors.initials: MS
authors.lastname: Westerterp-Plantenga
keywords: DIAAS; Indispensable amino acids; Nitrogen balance; Protein intake; Protein source