Found this on NHS site
Eat as soon as you can
The old advice was to not eat anything for a day or two, but now it is recommended that you eat foods high in carbohydrates (bread, pasta, rice or potatoes) and other foods as soon as you feel like it. Salty foods such as soup can help replace salt lost from your system.
If you feel you cannot eat, it shouldn't do you any harm, but make sure you continue drinking fluids and eat as soon as you are able