What Your Gut Has to Do with Your Breast Cancer Risk

By now you've heard a lot of news about gut bug, the microbes that live in your intestines and help digest food. The latest surprising findings indicate that gut bacteria could be instrumental in preventing breast cancer. "Preliminary research shows that gut bacteria seem to play a role in regulating a woman's estrogen levels," says James Goedert, M.D., who authored a recent study on the topic. That's important because too much estrogen in the blood has been shown to increase breast cancer risk, he explains.

In his study, Geodert found that healthy women who did not have as many kinds of gut bugs in their systems also had less estrogen in their urine than those with more diverse intestinal bacteria. This suggests that their bodies were not as efficient at flushing out excess levels of the hormone. (That's why science has us wondering: Is Better Gut Bacteria the Source of Overall Health and Happiness?)

Thanks to all the showering and fastidious hand washing we do, we transfer fewer bacteria to one another than we used to— so we're no longer exposed to a wide range of GI bugs, including the good ones. "We need to put more disease-fighting bacteria back into our intestines," Schiestl says. Fortunately, there are easy ways to help good gut bugs flourish—and they start with some of the healthy habits you already have in place.

Don't pack the same lunch every day. Different intestinal microbes thrive on different foods, so the best way to boost the types in your gut is to eat a varied, plant-based diet, says Carrie Daniel-MacDougall, Ph.D., a nutritional epidemiologist and an assistant professor at the University of Texas MD Anderson Cancer Center.

She suggests following long-standing guidelines that emphasize increasing fiber-rich plant foods. The USDA, for instance, advises eating at least 2 1⁄2 cups of vegetables a day from each of these groups: dark-green varieties (such as broccoli and spinach), red and orange produce (carrots and peppers), legumes (beans and peas), starches (corn and potatoes), plus bean sprouts, mushrooms, and onions. Also, try to limit your consumption of added sugars, which research shows may affect your gut bacteria. Instead, satisfy your sweet tooth with fruit. The USDA suggests eating 1 1⁄2 to 2 cups a day. (If you're the prep-ahead type, try these new meal prepping recipes to switch up the usual chicken and rice combo.)

Exercise can increase the diversity of your gut bacteria, according to a new review of several studies in the journal Frontiers in Physiology. The researchers think that working out may decrease the body's production of bile acids, which in turn lets microbes flourish, or increase its production of health-promoting short-chain fatty acids. Exercise may also reduce the amount of time it takes food to make its way through the intestinal tract, boosting GI bug diversity. (As if you needed another perk: exercise also makes you better in bed.)

Other evidence indicates that fit people have higher levels of a specific strain of bacteria that is known to reduce the risk of obesity, which is strongly linked to breast cancer. Experts don't yet know exactly how much exercise is good for your gut bugs, but they do have proof that it's essential to do workouts you enjoy. In a study on mice, only those that exercised voluntarily increased the diversity of their GI bugs, says Karen Basen-Engquist, Ph.D., the director of the Center for Energy Balance in Cancer Prevention and Survivorship at the University of Texas MD Anderson Cancer Center. The mice forced to work out against their will did not.

"Our ancestors ate 10 times more fiber than we do now," Schiestl says. This may help explain why their gut bacteria communities were far more robust. Aim for the recommended 25 grams of fiber a day, and be sure to incorporate chewy, stringy vegetables such as celery, asparagus, and artichokes into your diet. (Or try one of these high fiber recipes.)

"These foods contain resistant starch and other nutrients, which many of the healthy bacteria in your GI tract feed on," Daniel-MacDougall says. (Not yet convinced you need more fiber? This nutrient alone has been proven to reduce the risk of cancer.)

Look for supplements containing Lactobacillus and Streptococcus thermophilus strains of healthy bacteria. In a new study in the journal Applied and Environmental Microbiology, researchers found that these bugs were more plentiful in the breast tissue of healthy women than in those with cancer. They don't know for sure whether consuming these bacteria can help prevent the disease, but previous studies have shown that microbes can travel from your gut to your breasts, where they may help produce antioxidants that prevent the cellular damage that contributes to cancer, says Gregor Reid, Ph.D., one of the study's authors. Also smart: eating plenty of probiotic-rich fermented foods like kefir, sauerkraut and miso. (You'd be surprised how many types of food contain probiotics.)