<p> The increasing development of ingestible medical devices for gastrointestinal diagnostics, drug delivery, and physiological monitoring has created a growing demand for reliable and long-lasting power sources. Conventional batteries limit device lifetime, increase capsule size, and raise safety concerns, making biomechanical energy harvesting from gastrointestinal motility a promising alternative for self-powered ingestible systems. This review aims to provide a comprehensive overview of biomechanical energy harvesting from gastrointestinal mechanical activity for powering ingestible biomedical devices, with emphasis on energy sources, transduction mechanisms, materials, system integration, limitations, and future research directions. Recent literature on gastrointestinal biomechanics and energy harvesting technologies was analyzed, focusing on major transduction mechanisms such as piezoelectric, triboelectric, and electromagnetic generators. The review also evaluates material selection, device architectures, encapsulation strategies, and power management circuits from a system-level integration perspective. Piezoelectric, triboelectric, and electromagnetic energy harvesters demonstrate the ability to convert low-frequency gastrointestinal mechanical energy into electrical energy suitable for ultra-low-power biomedical devices. Hybrid energy harvesting systems improve energy reliability and output performance. However, several challenges remain, including low energy density, variability in gastrointestinal mechanical forces, miniaturization constraints, material durability, electrical conversion losses, and lack of standardized testing protocols. Biomechanical energy harvesting has significant potential to enable battery-free ingestible biomedical devices. Future developments in hybrid energy systems, ultra-low-power electronics, biodegradable materials, and adaptive power management are expected to support the development of fully autonomous self-powered ingestible medical devices.</p>