What's a good diet for someone to follow if they've recently undergone gastric sleeve surgery and they need to intake 600 calories per day?

Didnt u get info? I'm sure ur surgeon didnt put a sleeve in and run! get the info he gave u and follow it.
Sleeve diet . 600 calories is far too low for daily nutritional requirements. Yes it will make you lose weight but that is because it is starvation. You need around 1000 calories at a minimum. Most of your intake should be protein, veggies, fruits and only a small amount of carbohydrates.