Part of our job as registered dietitians (RDs) is to be detectives. Whether it is in the grocery store, analyzing food labels, or being weary of what we read in the media, we always have to be on our A-game. A, of course, stands for ANALYZING… We must stay on top of research studies and read them with a critical eye. Luckily, ample research linking cancer & dietary patterns exists and major organizations promote plant-based diets due to the ample evidence supporting a multitude of health benefits. Eating the plant-based way does not mean going full on vegan or vegetarian, but adding more cancer-protective fruits, vegetables, whole grains, nuts, seeds, and plant-proteins into your diet.
Can Breast Cancer Be Prevented by a Low Estrogen-Related Dietary Pattern?
A recent study in the International Journal of Cancer (IJC) has been stirring a lot of chatter within the cancer community. Researchers found that an “estrogen-related dietary pattern (ERDP)” might be associated with breast cancer risk [i]. The link with breast cancer was measured by two estrogen metabolites (EMs): the 2/16 ratio (estrogen metabolism ratio) and unconjugated estradiol (E2) (a compound linked to postmenopausal breast cancer). The EDRP included refined grains, tomatoes, “other vegetables: cucumber, onion, green pepper, beet, celery and lettuce”, cruciferous vegetables, cheese, yogurt, fish and shellfish high and low in omega-3s, franks and luncheon meat, nuts and seeds, and coffee [i].
The strongest correlation was seen between unconjugated E2 (“bad estrogen”) and refined grains, cheese, yogurt, and franks/luncheon meat. In addition, refined grains and cheese were also the only food groups with significant correlations with the 2/16 ratio [i].
In conclusion, a high ERDP was linked to higher unconjugated E2 and a lower 2/16 ratio. A follow-up period of 10.9 years identified 1,592 cases of breast cancer (mostly estrogen positive breast cancer) whereby these women had higher ERDP scores at baseline [i].
However, some critiques of the study include the lack of comparability to diverse populations and the limited food groups studied. Some studies question the validity of the 2/16 ratio hypothesis [ii]. Although this study has not shown a benefit in eating omega-3 rich fish and shellfish, many other studies have proven this to be true [iii].
There is no such thing as a “low-estrogen” diet, although you may find this on the internet (beware!). Post-menopausal overweight/obese women can lower estrogen by
- Regularly engaging in moderate-to-high intensity exercise
- Losing weight (a weight loss of 6-10% may lower estrogen levels)
- Eating a high-fiber low-fat diet and including cruciferous vegetables can influence estrogen levels. Women should be eating 3-5 servings of cruciferous veggies per week and at least 25-30 grams of fiber per day [iv]. If you’re eating a plant-based diet, you’re probably set with fiber goals
- Focus on families such as cruciferous vegetables: broccoli, cauliflower, cabbage, brussels sprouts, etc.; allium vegetables: onions, garlic, leeks; and Asian vegetables: bok choy and mixed mushrooms
- Mediterranean dietary patterns have much overlap with the plant-based diet and also show positive outcomes on breast cancer [iii]
- Alcohol: we know alcohol can raise estrogen levels in the body. The Continuous Update Project (CUP) published by AICR reviewed 112 studies including over 12 million women found “convincing evidence” to link alcohol intake to risk of postmenopausal breast cancer [v]
- Non starchy vegetables, carotenoid rich foods and calcium rich diets: the CUP also found “limited but suggestive” evidence that intake of these foods are protective [v]
- Dairy: although the IJC study found negative associations with cheese and yogurt, they did not differentiate fat content. Diets high in saturated fat are linked to higher risk of breast cancer [iv] [vi] [vii]
The Take Home Message
It feels like each month new studies about diet and breast cancer earn media attention. This study adds to the large body of research on diet & breast cancer, but more research is needed to affirm the results of this study. The IJC paper is not a “big picture” study, but may lead to some interesting data in the future. At this time, we are aware of some of the lifestyle factors beneficial for this population which could be helpful in terms of prevention.
Consult with an oncology-certified RD for more individualized guidance.