The convergence of fifth-generation (5G) wireless technology and the Internet of Things (IoT) is revolutionizing modern communication networks by enabling ultra-reliable, low-latency, and highthroughput connectivity. However, this rapid evolution raises critical concerns about energy consumption and sustainability, particularly as billions of interconnected devices become active. This paper investigates progressive trends in the integration of energy-efficient strategies within the 5G-IoT ecosystem. The study examines emerging technologies like edge computing, machine learning-based energy optimization, and energy harvesting techniques for their potential to balance performance and power consumption. The paper also discusses standardization efforts and green communication frameworks that guide the development of sustainable 5G-IoT infrastructures. Furthermore, real-world case studies and simulations are analysed to assess the impact of energy-efficient protocols and architectures on system performance. The results highlight that using a multi-layered strategy—mixing new network designs, energy management at the device level, and flexible protocols—is crucial for long-lasting sustainability. This research contributes to a more profound understanding of how next-generation IoT applications can align with global energy goals, paving the way for eco-friendly digital transformation. We also outline future directions for research and deployment, advocating for cross-disciplinary collaboration and policy support to enhance energy efficiency across the 5G-IoT spectrum.