진짜 빼야 되는데. => I really have to reduce (weight). 빼지 마. => Don't do that. - 빼다: subtract, reduce, withdraw, vacate, etc. - "2에서 1을 빼다": subtract 1 from 2. - "살을 빼다": reduce body weight. - "투자처에서 자금을 빼다": withdraw funds from an investment. - "방을 빼다": vacate a room. - 진짜(really) 빼야 되는데(must reduce weight). - 빼지 마: ~지 마 is a negative imperative form, like "don't (do something)". The first sentence is missing the object for 빼다 - subtract or reduce what? It might have been mentioned just prior. My guess is it is reducing weight (살을 빼야 되는데).