To shrink your waistline: Sit-ups and other ab exercises can help build muscle, but cardio is actually the most effective way to shrink belly fat, research has found. Reducing stress may help as well — stress causes a hormonal chain reaction that leads to belly-fat accumulation, says Mark Allen, co-author of Fit Soul, Fit Body: 9 Keys to a Healthier, Happier You. Source by grammymyrna