Energy efficiency is one of the major concerns of BSNs. Many energy efficient MAC protocols have been proposed. This paper considers adopting multi-hop communication in mobile swallowable BSNs for the first time. The paper evaluates multi-hop communication though the human body based on the IEEE 802.15.6 body channel model. The results showed that multi-hop communication saves energy consumption compared with single-hop communication when the circuitry power is small enough. Based on the result, the TDMA schedules for medium access are given in detail. The coordinator collects the neighboring information from sensors and calculates the routing and transmission power for each sensor. The sensors follow the schedules to finish data transmission. The proposed protocol avoids the idle listening, overhearing problem and most of the processing work is shifted to the coordinator. Simulation results showed the proposed TDMA protocol gives better performance than IEEE 802.15.6 in terms of energy consumption when the circuitry power becomes low. The main reason is that multi-hop communication makes the transmit power smaller and the corresponding adaptive power control. As the circuitry power becomes smaller due to new technologies, the proposed TDMA MAC protocol could be a good reference for energy efficient solution of BSN MAC standard. The future work would focus on slot assignment algorithm and hardware experiments.