Abstract: Abstrct: To address the high trans-fatty acid content and associated health concerns of traditional cake fats, this study developed the use of high-internal-phase emulsions (HIPEs) stabilized by a rutin-soy protein isolate (SPI) complex as a natural and functional fat substitute for bakery products. We systematically investigated evaluated the impact of the aqueous phase composition (native SPI, rutin-SPI complex) and oil phase composition (soybean oil, corn oil, coconut oil) on rheological behavior, structural integrity, microstructural homogeneity and oxidative stability of HIPEs. The results demonstrated that HIPEs stabilized by rutin-SPI complex outperformed native SPI-stabilized counterparts across all key metrics. Specifically, HIPEs stabilized by rutin-SPI complex exhibited significantly higher emulsifying activity index (EAI), emulsion stability index (ESI), and mechanical strength, with a storage modulus (G′) reaching 104.74 Pa, along with a marked reduction in malondialdehyde (MDA) content (P<0.05). Moreover, when soybean oil or corn oil was used as the oil phase, the emulsions displayed significantly enhanced EAI and ESI values (P<0.05) and a more compact network structure. Furthermore, HIPEs stabilized by the rutin-SPI complex with coconut oil as the oil phase exhibited excellent macroscopic layering stability, with the lowest creaming index (5.28%±0.29%) observed after 7 days of storage. Subsequently, HIPEs with different aqueous/oil phase combinations were incorporated into angel cake formulations to replace industrial shortening at substitution levels of 25%, 50%, 75%, and 100% (w/w). Notably, with both parameters decreasing as the substitution ratio increased, cakes prepared with rutin-SPI HIPEs showed significantly lower baking loss rates and shrinkage rates, which reduced to 1.11%±0.06% and 10.43%±0.11%, respectively (P<0.05). The overall sensory acceptability of these cakes was also significantly higher than that of cakes prepared with HIPEs stabilized by native SPI. Additionally, angel cakes formulated with 50% substitution of HIPEs stabilized by the rutin-SPI complex and coconut oil achieved the most desirable flavor profile. These findings establish a scientifically grounded and industrially feasible strategy for replacing unhealthy solid fats with plant-derived, antioxidant-enriched HIPEs in premium bakery products.