Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are long-chain polyunsaturated fatty acids (LC-PUFA) that can be obtained from the diet or synthesized endogenously from alpha-linolenic acid (ALA). Dietary protein was previously reported to influence the conversion of ALA into its downstream products. Specifically, in-vitro evidence showed that soy protein reduced delta-6 desaturase (D6D) activity compared to milk protein. Further, we recently found that young adults consuming soy-based foods had a lower D6D index compared to those consuming dairy foods. The aim of this human trial was to investigate the effects of milk protein isolate (MPI) and soy protein isolate (SPI) consumption on ALA metabolism. We hypothesized that SPI consumption would result in lower conversion of ALA into EPA and DHA compared to MPI. We completed a randomized, parallel-arm clinical trial in healthy men and women (n=16/sex; 18-45y), in which participants consumed two smoothies per day containing 30 g of either MPI or SPI for 30 days. On day 29, participants consumed a smoothie supplemented with a uniformly labeled 13C-ALA tracer, and blood and breath samples were collected over 24h to evaluate ALA desaturation and oxidation, respectively. Compound-specific isotope analysis (CSIA) by gas chromatography-isotope ratio mass spectrometry (GC-IRMS) will be used to determine the rates of EPA and DHA synthesis from ALA. Breath samples will be analyzed by IRMS to evaluate if dietary protein influences ALA oxidation. Expression of key genes that regulate the conversion of ALA into EPA and DHA will be measured by RT-qPCR in whole blood samples collected from participants before and after the 30-day trial. Analyses are ongoing and preliminary results will be presented. This study will provide important new insights regarding the role of dietary protein on ALA metabolism and its implications for omega-3 LC-PUFA synthesis.
2025. ISSFAL Quebec City June 30, 2025, Session 15: Dairy Fats, Submission 55 • ISSFAL 2025