Your not going to lose muscle by doing cardio… Only way you lose muscle is if you cut out working out all together…( but muscle memory will always be there)… Try bringing carrots, or broccoli or any other veggi with you during the day with a low fat dressing and eat that throughout the day… Try to stay away from fruits, only because most of them are high in sugars… Like mentioned above grilled chicken is great… You can season it anyway you like ( except dredged in bbq) and eat that with your veggi… Drink more water, 45% of your body is water, your muscles need water for repair and fuel ( too much will bloat you tho). Average person should drink about a gallon a day. And water weight is easy to lose. Thats why you see a lot of guys with gallon jugs of water.