In the first instance I would say yes, if you want to lose visceral fat on the inside you need to give your body a bit of a shock and 800 calories does that. Then when you feel that has taken effect (measure your waist and stomach as an indicator) you can maybe relax on the calories. But don’t eat the bad carbs.
My husband is 6ft 1inch and only weighs 13 stone. He has not been on this diet except he is forced to if he doesn’t want to do his own cooking. He does not stick to the 800 and has extra things like a bit of cheese most evenings or a fruit yogurt after lunch (I have no calories left for even a yogurt dessert) but when I have said do you want me to do you pasta/rice/mash with yours, he has said no just add some extra veg and a bigger portion of the chilli or whatever. As a consequence he has lost a little weight, nothing significant but on his annual well man check up he has reduced his cholesterol, blood sugars and triglycerides. I believe that is due to him not eating the bad carbs any more.