For me to lose weight pre-op and not have to worry about food, my doc put me on 3 protein shakes a day and a lean protein dinner. My cal intake is 900-1200 a day. 600 seems extreme, but if that is what they said then you should stick to it. Again, not attacking. Just seems odd, but everyone is different and I would be consumed by what I ate at that level. I think journaling and planning is the best way to go for anything. Good luck.