Women are bombarded with images of thin women with large breasts, but in real life, this body type is a rarity. Your breasts can get larger as you gain weight, and if you lose weight from hitting the treadmill or the pavement, your breasts might look a little smaller. Every woman is different, though, and there's no guarantee that slimming down through running will leave your breasts smaller.
Aerobic Exercise Basics
Running is a form of aerobic exercise. Aerobic exercise burns calories and can help you shed fat -- including in your breasts. If you run infrequently or make up for the calories burned running by eating high-calorie foods, you won't lose weight and your breasts will remain the same. But if you're running to try to trim down, your breasts could look different. The number of calories you'll burn running depends upon your weight, muscle mass, the intensity of your run and the amount of time you spend running. Harvard Health Publications estimates that you can burn between 200 and 700 calories in a 30-minute run.
Breast Tissue Composition
Breasts are made up of epithelial tissue that plays a role in breast-feeding and fatty tissue, which helps to cushion and support your breasts. The epithelial tissue will stick around no matter how much weight you lose, but you can shed some fat -- and therefore shrink your breasts -- with enough exercise. The degree to which your breasts will shrink depends on your breasts. Some women's breasts have more fatty tissue, while others have more epithelial tissue. If you don't have much fat in your breasts to begin with, you probably won't notice a major change, even with intense exercise.
Breast Size Basics
Even if the absolute size of your breasts decreases, losing weight can prevent your breasts from looking smaller. Breast size is a result of the size of the area just under your breasts as well as your breasts themselves. If you lose fat around your rib cage, your breasts could actually end up looking bigger. Even if your breasts shrink, losing fat in other areas of your body can make your breasts look larger or create the illusion that they didn't shrink at all.
Breast Health
It's easy to get caught up worrying about the effects exercise will have on your appearance, but aerobic exercise does more than just melt away fat. It can actually keep your breasts healthy. The National Cancer Institute emphasizes that four or more hours per week of exercise can help reduce your lifetime risk of breast cancer. To avoid pain in your chest and back, wear a snug-fitting, supportive sports bra that doesn't dig into your back or shoulders.
