I would drink water for 5 days. It's not too difficult. The hardest part is the boredom. I'm quickly reminded how much of my life revolves around food. Farmers market, grocery shopping, happy hours, cooking dinner, work lunches, events, etc. You suddenly have all this free time. For me, I just play a lot of golf to take my mind off of it.
If you want an easy version, look up fast mimicking diet by Dr. Longo. Prolon sells premade kits.