Het tekort verteerd: Een onderzoek naar eiwitinname, malabsorptie en spierbehoud na een bariatrische ingreep

Metabolic and bariatric surgery (MBS) induces substantial and durable weight loss, yet concerns persist about long-term muscle preservation and nutrient adequacy, particularly in older adults. Protein intake often decreases after surgery, while digestive adaptations may alter the handling of different protein sources. Selenium status may also influence muscle health after MBS, but data in older adults remain scarce. This thesis examined how older individuals (≥65 years) retain muscle mass and function after MBS, and to what extent protein intake, protein digestion, and trace element status contribute to these outcomes. Five complementary studies were undertaken. First, a cross-sectional comparison assessed the prevalence of sarcopenia, muscle mass, and muscle function in older adults with previous MBS versus non-surgical controls. Second, selenium status was evaluated in older adults with and without prior MBS. Third, a systematic review and meta-analysis synthesised evidence on muscle quantity, strength, and physical performance after MBS in studies without specific interventions to retain lean mass. Fourth, the dual-isotope tracer technique was used to compare digestion of spirulina protein in older adults with and without Roux-en-Y gastric bypass (RYGB). Finally, long-term protein requirements after RYGB were explored using the non-invasive Indicator Amino Acid Oxidation (IAAO) method. Across studies, older adults with prior MBS did not show a higher prevalence of sarcopenia than non-surgical controls. Low protein intake, higher adiposity, and age were more strongly associated with muscle impairment than surgical history. Selenium supplementation effectively increased selenium and selenoprotein P concentrations, though supersaturation occurred in some individuals. Protein digestibility appeared largely preserved after RYGB, and the IAAO protocol proved feasible in this population. Overall, adequate protein intake and appropriate supplementation support muscle preservation in older adults after MBS. These findings refine our understanding of nutrient metabolism and inform future updates of clinical nutrition guidelines for after bariatric surgery.