There’s a very good reason why it’s recommended that you get a bra fitting every six months — and that is that your breast size can change over time. There is a multitude of different factors that can come into play in causing your boobs to shrink or grow, some of which you may not even be aware of. One of the more obvious factors is genetics. Not only does heredity play a role in your body size and weight, but it also can affect how much fat is stored in your breasts.

Your genes aren’t the only thing that can cause your boobs to change size, however. If your bust line appears to be shifting, here are six lesser-known culprits that may be the reason. 

Your diet

As you may or may not know, your weight is connected to your breast size. This is because your breasts are primarily made up of fat, so the higher your body fat percentage, then the more likely your boobs are to be on the larger side. That said, it’s not always a direct correlation. Certainly, there are women who, despite having a lower weight, have large boobs, and vice versa. Though you’re probably aware of how gaining or losing weight can impact your breast size, what you may not know is that your diet can also play a part as well.

A 1997 study published in the Journal of the National Cancer Institute examined the effects of a low-fat, high-carbohydrate diet on the breasts. What researchers discovered is that women who decreased their consumption of dietary fat (to just 21% of their calorie intake) and increased their consumption of complex carbs (to 61% of their calorie intake) actually experienced a 6.1% decrease in breast density after two years. It’s worth noting that according to the study, areas of dense breast tissue have been linked to an increased risk of breast cancer.

Not only that, but Harvard Health reports that phytoestrogens — plant-derived chemicals that include soy, flaxseed, fennel, and alfalfa can impact breast size as well by attaching to cells’ estrogen receptors. Furthermore, soy-derived foods are chock-full of isoflavones, a particular kind of phytoestrogen that behaves just like estrogen in your body once you ingest it — and estrogen is one of the hormones that play a role in breast size.

Your chest workout

If you start noticing that your bust has been looking a tad fuller and perkier ever since you started cranking out all those pushups and dumbbell flyes, you’re not imagining things. Dr. Albert Matheny told SELF that by strengthening your pectoral muscles, which lie beneath the breast tissue, chest exercises can make your boobs project outward more. That explains why your button-up blouse doesn’t quite fit the same way after you’ve been doing regular chest workouts at the gym.

Birth control

Unless you did some research on the side effects of birth control before filling your prescription, you may not realize that this medication can affect your breast size.

This can happen for a number of reasons. First of all, birth control pills contain synthetic forms of the hormones estrogen and progestin, both of which can cause your breasts to grow in size. This change is usually most noticeable when you first start taking the pill. Not only that, but these hormones can also cause fluid retention in your body, which in turn can make your breasts appear engorged. But don’t fret — Healthline notes that these changes are typically only temporary, and you’ll likely go back to your regular breast size after a couple of months on the pill, once your body has gotten used to it. According to Healthline, if this is the reason why your birth control pill is affecting your breast size, they may return to normal once you start taking the inactive pills (also known as the placebo pills) at the end of your pack

Related: 5 Times When You Should Get A Bra Fitting

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Pregnancy and breastfeeding

It’s not just a myth — pregnancy boobs are a very legit thing, and you can thank hormonal changes for this phenomenon. In fact, studies have proven that it’s very normal to experience breast volume increases during pregnancy. But every woman is obviously different — while some may only notice a slight change in size as levels of progesterone, prolactin, and estrogen rise, others may grow up to two or three cup or band sizes.

Also, it’s extremely common for your breasts to swell up even more while breastfeeding, according to Johns Hopkins Medicine. They will often grow while the milk comes in, they will also usually return to their normal size again within a few months after you stop the weaning process.

Your period

Menstruation doesn’t just cause breast tenderness and soreness, it can also cause your breasts to look larger. Just as with pregnancy and birth control pills, this effect is due to an influx of hormones. Specifically, you’re most likely to notice this change in size during the luteal phase, which starts around day 15 of your cycle, right after ovulation. Gynecologist and hormonal expert Dr. Rebecca Booth told Health that progesterone levels are at their peak during this time, which is why your breasts may be at the largest size as well as density.

Caffeine consumption

Did you know that your daily coffee habit could actually have an effect on your bust line? According to the National Health Service (NHS), researchers at Lund University and Malmo University in Sweden found that consuming excessive amounts of joe is linked to shrinking breasts. Specifically, drinking three cups of coffee a day was enough to reduce a woman’s breast size. The NHS notes that while this study doesn’t prove that the coffee consumption caused the breasts to shrink, it does demonstrate an interesting association between the caffeinated beverage and reduced breast size.

Given that there are so many factors that can cause your breast size to change, it goes without saying that it’s crucial to get regular bra fittings. By getting measured every six months (or sooner if you’ve experienced pregnancy, breastfeeding, or significant weight gain/loss), you can make sure you’re buying bras that offer adequate support, coverage, and lift. Fittings are available at most department stores and independent lingerie boutiques and are almost always free of charge. Every woman deserves a bra that fits well — regardless of her fluctuating breast size.

Related: How Often Should You Change Your Bra?

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We Highly Recommend

Whether you’re shopping for new everyday bras or lingerie for a special occasion, it’s always a good idea to seek out a second opinion. We know how hard it is to find bras that fit well and feel good, especially when you’re doing it on your own. If you’ve ever felt unsure about your bra size or you just don’t know where to go to find good bras, it’s time to let a bra fitter help.

Many specialty lingerie boutiques offer bra fittings. Their expert bra fitters will take the pain and frustration out of bra shopping and do all the work for you. Even better, their product knowledge can save you time and money. Plus, they know where all of the best bras are hiding.

If you’ve struggled with finding bras in the right size, it’s time to make a change. Visit our specialty store locator to find a store near you and schedule an appointment.

Happy bra shopping!