Which sentence has a parallel structure?
the doctor recommends that you rest for a week and eating low-fat food at regular intervals.
the doctor recommends resting for a week and eating low-fat food at regular intervals.
the doctor recommends resting for a week and that you eat low-fat food at regular intervals.
the doctor recommends resting for a week and to eat low-fat food at regular intervals.
done

Parallel structure (also referred to as parallelism) connotes uniformity in grammatical pattern in a sentence which creates a clear and easy to understand flow of multiple ideas with equal level of importance. It is a way to enumerate a list of items in a coherent manner.

Based on the definition above, the correct answer is:

The doctor recommends resting for a week and eating low-fat food at regular intervals.