Your body turns to proteins (muscle) after the immediate fuel source (the food you ate) is used up. That's why it's important to have exercise as an important part of any weight loss journey. If you do a bit of resistance training (even just squats and using cans to do bicep curls, etc.), you can keep the muscle you have (or build a little more to burn more calories - muscle is a very efficient calorie burner!) and lose the fat.
Hope that helps!