I went from eating about 3000 calories a day to exante and I've managed fairly well! Was 100% the first week but then went to a funeral and forgot to take a bar and so ate at the buffet (did stick to water though so quite proud) as long as you plan ahead with shakes/soups/bars then it should be easier considering you've only been having one meal a day - I guess you'd go further into ketosis without the meal so should be quite easy too (don't quote me, its just a guess!) Good luck anyway!!!