Although you may appear thinner when you wear a girdle, the girdle doesn't strengthen or tone your abdominal muscles. Girdles just temporarily compress and redistribute fat and skin around the abdomen. When it comes to a flat stomach, diet and exercise — not undergarments — are what count.
Dietary changes and aerobic exercise can help you shed unwanted pounds, including those around your middle. Although it takes aerobic activity to burn fat, core exercises can strengthen and tone the underlying muscles. Examples of core exercises are the abdominal crunch and the bridge. But any exercise that uses the trunk of your body without support counts, including Pilates and fitness ball exercises.