Synergistic Effects of Microencapsulated Polyphenols and Concurrent Training on Metabolic Health and Fitness in Overweight/Obese Adults with Prediabetes

<b>Background/Objectives</b>: Prediabetes markedly increases the risk of progression to type 2 diabetes. While exercise and dietary polyphenols independently enhance metabolic health, their combined and synergistic effects remain unclear. This randomized, single-blind, placebo-controlled trial investigated the synergistic effects of concurrent training and a microencapsulated persimmon-karonda polyphenol formulation on glycemic control and inflammatory outcomes in adults with prediabetes and who are overweight/obese. <b>Methods</b>: Forty-three participants completed the intervention and were assigned to placebo, concurrent training (CBT), supplementation (EATME), or the combined intervention (CBT + EATME) for 8 weeks. Primary outcomes included fasting blood glucose (FBG), glycated hemoglobin (HbA1c), homeostatic model assessment for insulin resistance (HOMA-IR), high-sensitivity C-reactive protein (hs-CRP), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), adiponectin, physical fitness, and quality of life (QoL). <b>Results</b>: All intervention groups (CBT, EATME, and CBT + EATME) showed improvements in glycemic indices, with the greatest reductions in FBG (<i>p</i> < 0.01), HbA1c (<i>p</i> < 0.05), and HOMA-IR (<i>p</i> < 0.01) observed in the CBT + EATME group compared with placebo. All interventions significantly reduced hs-CRP (<i>p</i> < 0.01) and IL-6 (<i>p</i> < 0.01), accompanied by marked increases in adiponectin (<i>p</i> < 0.01), compared with placebo. In the CBT + EATME group, reductions in hs-CRP were positively correlated with improvements in HOMA-IR (<i>r</i> = 0.627, <i>p</i> < 0.05). Both CBT and CBT + EATME improved muscular strength and maximal oxygen consumption (<i>V̇</i>O₂max), with the combined intervention producing greater gains in upper- and lower-body strength (<i>p</i> < 0.05), <i>V̇</i>O₂max (<i>p</i> < 0.05), and the psychological well-being domain of QoL (<i>p</i> < 0.05) compared with placebo. <b>Conclusions</b>: These findings highlight that combining concurrent training with microencapsulated polyphenol supplementation produced the most consistent improvements across metabolic, inflammatory, and fitness outcomes, supporting this combined approach as an integrated and synergistic strategy to reduce diabetes risk and promote overall health in at-risk adults. The trial was registered at the Thai Clinical Trials Registry (TCTR20250512003).