(PTFS09-03-25) Dual-Tracer Approach to Study Differences in Amino Acid Digestibility Between Old and Young Adults

Objectives: Meeting the amino acid (AA) requirements is crucial for older adults to prevent development of sarcopenia. Older adults are suspected to have reduced AA digestibility, however, there is limited in vivo evidence. This study aimed to determine the difference in AA digestibility of milk, sorghum and black beans between older (65-80 years) and younger (20-35 years) adults using the dual-tracer method.

Methods: The study was executed in 10 young and 10 older adults. Participants ingested 20g intrinsically ²H-labelled protein (from milk, sorghum or black beans) with 400mg ¹³C-labelled amino acid mixture in a plateau feeding protocol on three separate test days. The ratio between ²H and ¹³C enrichment of the indispensable AA in blood plasma was analysed between 5.5 and 8 hours frequent feeding and compared between the two age groups, as a proxy of digestibility.

Results: Combining the three protein sources, the ²H/¹³C ratio was numerically lower in older compared to young adults for 7 out of 8 measured indispensable AA (Val, Leu, Ile, Met, Phe, His, Thr, not Lys), ranging from 0.7% for Ile to 13.2% lower in older adults for Leu, an amino acid important for muscle protein synthesis. Therefore, mixed model analysis was performed for Leu and showed significant age effect, with the ²H/¹³C ratio being 0.106 lower for older adults (p=0.005). This reduction aligns with the hypothesized lower digestibility in older adults, as the ²H/¹³C ratio in the meals was expected to be similar between participants.

Conclusions: These results provide an indication of lower digestibility in the older adults for some indispensable AA, that should be confirmed by completion of the meal analyses to the principles of the dual-tracer approach. These data indicate at least that the dual-tracer approach can be applied to investigate differences in AA digestibility between young and older adults. Quantifying these differences in digestibility upon ageing provides essential information for product formulation and dietary advice to an older population.

Funding Sources: This work is part of the project ‘Quantifying differences in bioavailability of different dietary proteins in older adults’ co-financed by the Top Consortium for Knowledge and Innovation Agri & Food by the Dutch Ministry of Economic Affairs under contract number LWV20155.