"Strangely I did not feel weak or less able because of it."
You were probably getting a substantial amount of energy from metabolizing body fat.
As suggested by other posters, energy drinks are a good source of carbs in the absence of appetitite. There are many to choose from. Also soupy meals, as per Roger Caffin, e.g. potato soup, pea soup, thinned out refried bens, corn chowder.