Novel Advances in Bioactive Components and Pharmacological Effects of Guava (Psidium guajava L.) Fruits and Leaves: A Review of Progress over the Past Five Years

The fruit of guava (Psidium guajava L.) comes from a tropical plant with both edible and health-beneficial values. Guava leaves are often processed into guava leaf tea for consumption. Its fruit and leaves contain polysaccharides, phenolic acids, flavonoids, terpenoids, vitamins, and minerals, but the strength of evidence varies markedly across preparations and outcomes. This review critically evaluates studies published mainly during the past five years and links organ-specific composition, extraction conditions, mechanisms, preclinical outcomes, clinical evidence, and product development. Reported guava leaf total phenolic contents range from 53.24 to 438.80 mg gallic acid equivalents/g, while guava leaf polysaccharides showed a DPPH-scavenging rate of 65.43 ± 2.56% and α-glucosidase IC₅₀ values of 790–904.67 μg/mL in preclinical assays. Mechanistically, phenolic compounds and polysaccharides may directly scavenge radicals and modulate Keap1–Nrf2–ARE, PI3K–Akt–GLUT4, NF-κB, and carbohydrate-hydrolyzing enzymes; guajadial and guaijaverin provide compound-level examples, although most causal evidence remains biochemical, cellular, or animal-based. Four randomized studies (n = 31–120) reported changes in postprandial glucose, blood lipids, blood pressure, inflammatory indices, or viral-clearance time, but heterogeneity, short follow-up, incomplete blinding, and predominantly healthy or mildly affected populations preclude firm clinical conclusions. Compared with earlier descriptive reviews, this review integrates fruit–leaf similarities and differences, explicitly appraises evidence strength and study limitations, and connects composition and processing to biological function and translation. Standardized extracts, exposure–response studies, and adequately powered multicenter trials are priorities for determining efficacy, safety, and practical value.