In battery powered systems such as wireless sensor networks, energy efficiency is one of the most important system design goals. In this paper, energy efficiency is examined from the perspective of data consistency, which includes both temporal consistency and numerical consistency, and considers the application specific requirements of the data and data dynamics in the data field. We first formally define the energy-efficiency problem with the goal of delivering a minimum number of messages under the constraint of data consistency. Then, we give the formal definition of the data consistency. To achieve both consistency and energy efficiency, we propose a data collection protocol named Alep, which adapts the data sampling rate to the data dynamics in the data field and keeps lazy when the data consistency is maintained. From the results of a comprehensive simulation we find that the proposed approach indeed reduces the number of delivered messages by more than 20%, and impr...