Final answer:
The initial step in planning care for an obese client who wants to lose weight is obtaining a 24-hour dietary recall to assess current eating patterns before making any further interventions.
Step-by-step explanation:
The first action a nurse should take in planning care for a client who is obese and wishes to lose weight is to obtain a 24-hr dietary recall. This step is crucial as it provides a baseline of the client's current eating habits and can indicate areas where dietary modifications can be made. The other options are important aspects of weight loss plans—recommending weekly weigh-ins, creating an exercise plan, and initiating a diet modification plan—but establishing the client's current dietary intake is the foundational information required before other aspects of interventions can be personalized and implemented effectively.