Which of the following is a key indicator of poor dietary intake in a postpartum client?

Dehydration is indeed a key indicator of poor dietary intake in a postpartum client. During the postpartum period, it is crucial for new mothers to maintain proper hydration as it significantly affects their recovery and overall health. Adequate fluid intake supports lactation, helps to prevent constipation, and aids in the body's healing processes after delivery. Dehydration can lead to complications such as decreased breast milk production, increased fatigue, and even urinary tract infections, all of which can hinder a new mother's ability to care for herself and her baby.

In contrast, the other options suggest more positive outcomes. Increased energy levels are typically associated with proper nutrition and rest. Weight gain, when appropriate, can reflect healing and recovery, especially if the mother is nourishing herself adequately. A stable body temperature might indicate good overall health and proper bodily function, which would likely not correlate with poor dietary habits. Thus, dehydration serves as a significant warning sign of insufficient nutritional and fluid intake during the critical postpartum phase.