Measuring breast size. Image Credit: moodboard/Cultura/Getty Images

You diet and exercise faithfully, but the fat in your hips, buttocks and thighs refuses to budge. Your breasts, however, seem to shrink right before your eyes. As women move from girlhood to adolescence, all of these areas of the body begin to store more fat due to hormonal changes that support childbirth and breastfeeding. The effect of weight loss on your breasts depends on how much of this fatty tissue you have stored there.

About Breast Tissue

Fat tissue often makes up the majority of tissue in the breasts; the fat cells expand as you gain weight. People with larger chests have more fat tissue, not more duct or lobule volume, which is the lean tissue required for breastfeeding. When you drop pounds, the cells in the fat tissue shrink along with other such cells in your body. Losing weight can have a noticeable impact on the size of your breasts if you tend to have a lot of fatty tissue stored there. Some women have denser breasts with less fatty tissue, and they'll experience less noticeable drops in breast size as they lose weight. Your genetics determine the amount of fat tissue in your breasts and their subsequent size. The only way to find out if you have dense or fatty breasts is through medical imaging, such as a mammogram.

Overall Body Size and Your Breasts

A 2012 study published in the American Journal of Human Biology determined that women with larger breasts tend to weigh more, have a higher body mass index and more body fat than women with smaller breasts. Shape magazine notes, though, that it takes losing about 20 percent of your weight to drop an entire cup size. A woman who weighs 160 pounds would need to lose 32 pounds to see this change, for example.

Weight Loss and Breast Sag

Women who lose extreme amounts of weight -- such as in cases of bariatric surgery for morbid obesity -- may experience significant shrinkage in the size of their breasts. The breasts may subsequently appear smaller and saggier as the skin and supportive tissue in that area stretches out.

Chronic yo-yo dieters may also experience significant sag as a result of the constant gain and regain of weight. When you lose weight quickly, the elastin and collagen that support your breast tissue experience stress, causing them to break down rapidly. Put these proteins under the constant stress of losing and regaining pounds, and they deteriorate prematurely, leaving your breasts permanently flaccid.

Healthy Weight Loss and Breast Size

Lose weight at a slow, sustainable rate, and your breasts will experience less impact. Shedding a pound or two per week doesn't create as much stress for collagen and elastin. You're also more likely to be using safe and smart measures such as exercise and moderate portions of whole, unprocessed food, such as lean proteins and leafy greens. These strategies can lead to long-term habit changes that help you maintain the weight loss.