Metabolic Availability of Lysine in Milk and a Vegetarian Cereal–Legume Meal Determined by the Indicator Amino Acid Oxidation Method in Indian Men

Abstract

Background Lysine rich foods such as milk and legumes serve as important food additions to the lysine deficient cereal-based diets of vegetarian populations in low- and middle-income countries (LMICs) to alleviate the risk of quality corrected dietary protein inadequacy. Dietary protein quality can be determined by estimating the metabolic availability (MA) of lysine. Objectives The study aimed to estimate the MA of lysine in spray-dried cow milk powder (SMP), heat-treated spray-dried cow milk powder (HSMP), and a habitually consumed cereal-legume based vegetarian meal (VM), using the indicator amino acid oxidation (IAAO) slope-ratio method. Methods The MA of lysine in SMP, HSMP, and VM was estimated in 7 healthy young men aged 19–24 y with BMI of 21.5 ± 0.5 kg/m2 in a repeated measures design. The IAAO response slopes with 2 graded lysine intakes (10.5 and 15.0 mg·kg−1·d−1) from the SMP and VM were compared with the response slope generated with 3 graded crystalline lysine intakes (6.0, 10.5, and 15.0 mg·kg−1·d−1) at the subrequirement level. To produce HSMP, pasteurized cow milk was heat treated and spray dried. The MA of lysine in HSMP was tested at a single level of lysine intake (15 mg·kg−1·d−1). A total of 8 IAAO experiments were conducted on each participant in randomized order. The IAAO slopes were estimated using a linear mixed-effect regression model. Results The MA of lysine in SMP, HSMP, and VM was 91.9%, 69.9%, and 86.6% respectively. Conclusions Heat treatment reduced the MA of lysine by 22% in HSMP compared with SMP in healthy Indian adults. The lysine MA estimates can be used to optimize lysine limited cereal-based diets, with the addition of appropriately processed legumes and milk powder, to meet the protein requirement. This trial was registered at Clinical Trials Registry of India (http://ctri.nic.in) as CTRI/2019/08/020568.

Evaluation of Protein Quality in Humans and Insights on Stable Isotope Approaches to Measure Digestibility – A Review

“…A PubMed search using key terms of “amino acid metabolic availability” OR “amino acid bioavailability” AND “indicator amino acid oxidation” AND “humans,” was performed to obtain MA of IAAs in different proteins, as measured in humans, and the results are presented in Supplementary Table 1 . The method does not report interindividual variability of the MA estimates, however, the CV appears to range from 15% to 52% across the studies when the SE of the slope was considered ( 70 , 72 , 73 , 75 ). Nevertheless, the method provides reasonable MA estimates for foods and as expected, has been found to be lower than true ileal IAA digestibility or TAAD values ( 23 , 43 , 59 , 72–74 ), except for rice, which could be due to the differences in milling processes ( 73 , 75 , 76 ).…”

“…The method does not report interindividual variability of the MA estimates, however, the CV appears to range from 15% to 52% across the studies when the SE of the slope was considered ( 70 , 72 , 73 , 75 ). Nevertheless, the method provides reasonable MA estimates for foods and as expected, has been found to be lower than true ileal IAA digestibility or TAAD values ( 23 , 43 , 59 , 72–74 ), except for rice, which could be due to the differences in milling processes ( 73 , 75 , 76 ).…”