I lost over 80 pounds through fasting and did not lose strength in fact gained it. I did longer fasts mostly but now I do alternate day fasting. I was eating nothing every other day for a long time but now I do one ~500 calorie meal every other day and it works just as well with fewer hassles. The idea is your body does not shut down the metabolism from short term deprivation like it will from longterm deprivation in fact in the short term it increases the metabolism, so you can lose weight without tanking your metabolism and gaining it all back like all the people from that show the biggest loser did.