Background & aims: Upper-body, i.e. visceral, obesity is associated with insulin resistance and impaired protein synthesis. It is unclear whether postprandial stimulation of protein synthesis is affected by body fat distribution. We investigated the postprandial protein anabolic response in a cohort of obese women.
Methods: Participants were studied after an overnight fast and after a mixed meal, grouped as upper-body obese (UBO, waist-to-hip ratio, WHR, >0.85, n = 6) vs. lower-body obese (LBO, WHR <0.80, n = 7). Lipid and carbohydrate metabolism were assessed by measurements of plasma free fatty acids (FFA), insulin and glucose plasma concentrations, and calculation of the Quicki index from fasting glucose and insulin values. Different labels of stable isotopes of phenylalanine were administered intravenously and orally, and leg and whole-body protein breakdown and synthesis were calculated from phenylalanine/tyrosine isotopic enrichments in femoral arterial and venous blood, using equations for steady-state kinetics. Data are denoted as mean ± SD.
Results: Age (38 vs. 40, p = 0.549) and body-mass index (33.7 ± 1.9 vs. 35.0 ± 1.8, p = 0.241) were similar in both groups. UBO subjects had more visceral fat (p = 0.002) and higher fat-free body mass (FFM) (p = 0.015). Plasma insulin concentrations were greater in UBO than LBO women (p = 0.013), and UBO were less insulin sensitive (Quicki = 0.32 ± 0.01 vs. 0.36 ± 0.02, p = 0.005). Protein kinetics across the leg were not different between groups. Fasting whole body protein balance was similarly negative in both groups (UBO -6.5 ± 2.4 vs. LBO -7.6 ± 0.9 μmol/kgFFM/h, p = 1.0). Postprandially, whole body protein balance became less positive in UBO than in LBO (14.8 ± 3.7 vs. 20.2 ± 3.7 μmol/kgFFM/h, p = 0.017).
Conclusions: Whole-body protein balance following a meal is less positive in upper-body obese, insulin-resistant, women than in lower-body obese women.
Keywords: Protein synthesis; Stable isotope labeling; Upper-body obesity.
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