The muscle you have is not there forever. if you don't feed it and don't use it - you lose it. a proper plan with right combination of resistance and cardiovascular training with adequate progression and a right nutrition plan to support it can help you achieve this. exercise only boosts the burning process but doesn't just melt the fat away on its own - if you do not create a deficit and feed the body too much - it won't touch the stored fuel reserves. on the hand if you drastically cut your calories and do not feed your muscle properly or don't exercise and use your muscle, you will lose it. fat loss is about finding that right balance.