Effect of food form on postprandial plasma amino acid concentrations in older adults

To assess the effect of food form (FF) on postprandial (PP) plasma amino acid (AA) concentrations, ten older adults (five men and five women, age 72 (sem 2) years, BMI 26.0 (sem 0.9) kg/m2) consumed, on separate days, energy and macronutrient-matched test meal replacement products (MRP) (approximately 25 % of the subject's daily energy need; approximately 54 % carbohydrate, 21 % protein, 25 % fat) in beverage and solid form. Blood samples were taken during fasting and throughout the 4 h PP period; plasma AA concentrations were assessed using HPLC. Consumption of each MRP led to an increase in total AA, branched-chain AA (BCAA), essential AA (EAA), non-essential AA (NEAA) and leucine concentrations (4 h area under the curve, AUC) (time effect; P < 0.05). The beverage MRP resulted in a greater initial (i.e. 30 min) and sustained (4 h AUC) increase in total AA, BCAA, EAA, NEAA and leucine concentrations compared with the solid MRP (each effect of FF; P < 0.05). Although there was no effect of FF on PP insulin response, glucose concentration was greater 1 and 2 h after the solid MRP was consumed (FF × time interaction; P < 0.05). For all PP time points combined, total AA concentration was positively associated with plasma insulin (r 0.25) and glucose (r 0.24) concentrations for the solid MRP but not for the beverage MRP. In conclusion, older adults can achieve higher plasma AA concentrations when a protein-containing MRP is ingested in beverage form. The implications of the higher AA availability on anabolic processes warrant investigation.