(P04-024-25) Comparative Effects of Lacto-Vegetarian and Vegan Diets on Muscle Protein Synthesis and Plasma Metabolomics in Healthy Older Adults at and Above the RDA

Objectives: Dairy products provide high-quality protein that can be incorporated into vegetarian diets and improve health outcomes. However, the effect of adding higher-quality protein, such as dairy, to a vegan diet on muscle protein synthesis (MPS) in free-living older adults has not been studied. We aimed to determine how adding dairy to a vegan diet would affect MPS. We hypothesized that incorporating dairy into a vegan diet would enhance MPS compared to a diet with only plant-derived proteins but with equal protein content. We also hypothesized that a higher daily protein intake greater than the RDA would increase MPS and impact the metabolome.

Methods: Forty healthy older participants (average age 70 ± 4 years) were divided into two groups and randomized to one or two protein intakes: 0.8 g/kg (Recommended Dietary Allowance: RDA) or 1.2 g/kg per day (1.5x RDA). Each group followed two 17-day vegetarian diets—one entirely plant-based (vegan; V) and the other lactovegetarian (LV), which included dairy products (cheese, milk, and yogurt) to replace 30-32% of plant protein. Diet order was randomized, with a 7-day washout in between. Participants' food intake, body composition (DXA), and physical activity (accelerometry) were assessed. Participants ingested deuterium oxide, and we measured MPS by combining it with muscle biopsies. Blood samples were taken on days 4 and 17 of each diet for plasma metabolomic analysis.

Results: Thirty-two participants, 16 per group, completed the protocol and were included in the analyses. No significant changes were observed in lean mass. Mixed MPS was higher when participants ingested LV diets than vegan diets for both daily protein intakes and was higher at 1.5x RDA than RDA (0.8: 1.26% ± 0.06 vs. 1.33 ± 0.08; and 1.2:1.32% ± 0.07 vs.1.41% ± 0.11, P< 0.05). Daily protein intake at 1.5x RDA changed the plasma metabolomic profile versus the RDA but was unaffected by dairy.

Conclusions: In line with our hypotheses, mixed-MPS was higher in older participants who ate LV diets with both levels of daily protein intake. Mixed MPS was higher when ingesting 1.5x RDA than the RDA. Finally, plasma metabolome was significantly different comparing 1.5x RDA vs RDA, but no major changes were observed when only including dairy.

Funding Sources: US National Dairy Council and Dairy Farmers of Canada