To get a slimmer body, you need to lose fat, not muscle!
To lose weight it's important to walk 1 hour regularly; and you won't lose weight like you would on a diet. Muscles burn calories naturally. Thanks to your endurance workouts, they develop and consume even more. It's the virtuous circle triggered by fitness walking - which carries on if you stay motivated!
Note: muscles are heavier than fat, so your weight loss will not necessarily show on the scales as your muscles develop. This is why it is preferable to focus on the change in waist size, which you can record in your training log, rather than weight, as recommended by the sports physician, Charles Aisenberg.