Basal and postprandial myofibrillar protein synthesis rates do not differ between lean and obese middle-Aged men

Background: Excess lipid availability has been associated with the development of anabolic resistance. As such, obesity may be accompanied by impairments in muscle protein metabolism. Objective: We hypothesized that basal and postprandial muscle protein synthesis rates are lower in obese than in lean men. Methods: Twelve obese men [mean ± SEM age: 48 ± 2 y; BMI (in kg/m²): 37.0 ± 1.5; body fat: 32 ± 2%] and 12 age-matched lean controls (age: 43 ± 3 y; BMI: 23.4 ± 0.4; body fat: 21 ± 1%) received primed continuous L-[ring-²H₅]-phenylalanine and L-[ring-3,5-²H₂]-Tyrosine infusions and ingested 25 g intrinsically L-[1-¹³C]-phenylalanine labeled whey protein. Repeated blood and muscle samples were obtained to assess protein digestion and amino acid absorption kinetics, and basal and postprandial myofibrillar protein synthesis rates. Results: Exogenous phenylalanine appearance rates increased after protein ingestion in both groups (P < 0.001), with a total of 53 ± 1% and 53 ± 2% of dietary protein-derived phenylalanine appearing in the circulation over the 5-h postprandial period in lean and obese men, respectively (P = 0.82). After protein ingestion, whole-body protein synthesis and oxidation rates increased to a greater extent in lean men than in the obese (P-interaction < 0.05), resulting in a higher whole-body protein net balance in the lean than in the obese (7.1 ± 0.2 and 4.6 ± 0.4 μmol phenylalanine · h^-1 · kg^-1, respectively; P-interaction < 0.001). Myofibrillar protein synthesis rates increased from 0.030 ± 0.002 and 0.028 ± 0.003%/h in the postabsorptive period to 0.034 ± 0.002 and 0.035 ± 0.003%^.h^-1 in the 5-h postprandial period (P = 0.03) in lean and obese men, respectively, with no differences between groups (P-interaction = 0.58). Conclusions: Basal, postabsorptive myofibrillar protein synthesis rates do not differ between lean and obese middle-Aged men. Postprandial protein handling, including protein digestion and amino acid absorption, and the postprandial muscle protein synthetic response after the ingestion of 25 g whey protein are not impaired in obese men. This trial was registered at www.trialregister.nl as NTR4060.