Impact of quantity and source of dietary protein intake within a healthy dietary pattern on cardiovascular disease risk factors in Singapore older adults: a randomized controlled trial

<i>Background</i>: A higher protein diet (HPD) is recommended for older adults to support their muscle mass maintenance, but its cardiovascular protective effects in this population remain controversial, potentially due to differences in protein sources. <i>Objective</i>: To investigate the effects of HPDs with different sources within a healthy dietary pattern (HDP) on conventional cardiovascular disease (CVD) risk factors and vascular health-related outcomes in Singapore older adults. <i>Methods</i>: In this 16-week randomized controlled trial, 55 participants were assigned to one of the three groups: following a HDP alone (Control, <i>n</i> = 19), following a HDP supplemented with 20 g day^-1 of either casein protein isolate powder (HPD-CP, <i>n</i> = 18) or soy protein isolate powder (HPD-SP, <i>n</i> = 18). Blood pressure, lipid-lipoprotein profiles and composite CVD risk indicators were evaluated at the baseline and post-intervention. Parameters of vascular function (flow-mediated dilation) and vascular regeneration (endothelial progenitor cell percentage and blood outgrowth cell functions) were also assessed. <i>Results</i>: The Control group exhibited significant increases in triglyceride levels (+0.33 ± 0.1 mmol L^-1) and composite CVD risks (atherogenic index: +0.31 ± 0.11; Framingham predicted long-term CVD risk: +0.8 ± 0.43%). In contrast, both HPD groups showed maintenance of the lipid-lipoprotein profile and CVD risk predictors, with further significant reduction in the total cholesterol level in the HPD-SP group (-0.28 ± 0.12 mmol L^-1). All groups showed significant increases in CD34⁺ cell expression, and particularly, the HPD-SP group demonstrated potential to enhance the angiogenic capacity of blood outgrowth endothelial cells. However, no changes were observed in other vascular functions and vascular regeneration parameters. <i>Conclusions</i>: Adherence to an HPD, particularly from soy protein, within an HDP supports the maintenance of the lipid-lipoprotein profile and CVD risk predictors among Singapore older adults. These findings highlight HPD as a potential dietary strategy to promote cardiovascular health when adhering to an HDP in older adults; however, the source of protein may influence its effectiveness. This study was registered at clinicatrials.gov as NCT05400005.