Breasts are made up of fatty tissue, so when body fat levels decrease, so too does breast size. To lose body fat, a woman needs to burn more calories than she consumes, states notes ShapeFit. Moderate to high-intensity aerobic exercises, such as running, jogging, cycling, swimming, kickboxing and rowing, helps burn fat. Light strength training exercises targeting the pectoral muscles, such as push-ups and the bench press, can also tone the chest, making it appear smaller.
Chest exercises targeting the pectoral muscles can sometimes increase breast size by enlarging the muscles and lifting and defining the chest, cautions The Nest. Therefore, it is important not to use weights that are too heavy, as this may lead to faster muscle build-up and the appearance of larger breasts, according to ShapeFit.
In addition to exercising, dieting is also important, notes ShapeFit. Reducing daily intake of fats and sugars can help reduce body fat. To lose 1 pound of fat, women must eliminate 3,500 calories from their diet through a combination of careful eating and exercise. Reducing chest size through diet and exercise alone may not work for everyone, however, so some women, especially those with a petite body type, may consider breast reduction surgery.