lrb I totally agree that if you feel hungry, eat more of the low carb food. You'll remain in ketosis and burning body fat, which you won't if you grab bread or booze etc.
A couple of days per week, even on 1500 cals low carb, could make this WOE more sustainable but still keep you losing steadily.
Ernest, moo Try just having brunch / lunch and supper for your 800 cals.
It doesn't matter if those on BSD 5:2 or 4:3 are well under 800 cals on FDs, because they eat plenty the other days.
However, Ernest on daily BSD, you do need to aim for 800 cals, so you obtain sufficient nutrients. Try these:
Healthy low carb high cal food:
. Avocado
. Hummus, taramasalata, tzatziki
. Oily fish, e.g. salmon, mackerel
. Full fat Greek yoghurt
. Berries with cream
. Drizzle olive oil on salad or roast veg
. Piece of hard cheese
. Cheese omeletee
. Bacon, eggs, tomato, mushroom fryup
. For those not allergic- unsalted nuts, nut butters without added sugar / palm oil