Answer:
The doctor is requesting that the patient eat a healthy diet.
Step-by-step explanation:
Three categories of the subjunctive: 
1.Wishes, Desires, and Hopes 
2.Requests 
3.Doubts and Fear 
 
Guidelines for the subjunctive to happen: 
1.A change of subject 
2.A specific verb category in the main clause 
3.The word “que” which in this case means “that” 
 
 
Example:Yo espero que mi mamá cocine la cena. 
 
In this example all of the three guidelines are present: 
1.Change of subject: Yo espero que mi mamá cocine la cena. 
2.Trigger verb: espero 
3.The que between the main clause and the dependent clause