When it comes to reducing the risk of breast cancer, especially in younger women, there’s no shortage of advice: stay active, keep a healthy weight, drink less alcohol, and eat well. But what does “eat well” really mean? We tend to think about food in terms of calories, nutrients, or how satisfactory it is; but rarely do we stop to consider how our daily meals might be shaping the invisible workings of our bodies, like hormone levels. And yet, for women under 50, that connection might matter more than we realize, especially when it comes to breast cancer.
Scientists have long suspected that what we eat might influence breast cancer risk in younger women, possibly by affecting the body’s natural hormone levels. While some research has explored individual dietary components such as alcohol or fiber, far fewer studies have looked at overall eating patterns and how those habits might relate to hormone fluctuations. A recent study, published in Breast Cancer Research and Treatment, looked at dietary patterns and assessed whether those habits aligned with levels of hormones known to play a role in cancer risk.
Dr. Holly Harris and postbacc scholar Sable Fest at Fred Hutch Cancer Center used data from the long-running Nurses’ Health Study II, which has been following the health of over 116,000 women since the 1989. They analyzed dietary surveys and hormone levels from a smaller group of around 2700 women, then tracked breast cancer diagnoses in the full group over the next 24 years. It’s one of the largest studies of its kind to date.
They began by examining whether foods and food groups were related to five specific hormones, including estradiol and estrone, which are forms of estrogen. These hormones naturally fluctuate during a woman’s menstrual cycle; but consistently high levels especially in the luteal phase—the second half of the cycle—have been linked to a greater risk of developing breast cancer before menopause.
In their analysis, two dietary patterns in particular stood out. One of them was linked to higher levels of luteal-phase free estradiol—a form of estrogen measured during the second half of the menstrual cycle, after ovulation. Women who had higher levels of this hormone consumed more alcohol, fruit juice, and cream-based soups. The other pattern was tied to higher estrone levels in the follicular phase, the first half of the cycle that starts with menstruation and ends at ovulation, when estrogen levels are naturally rising. This dietary pattern included more fruit juice, egg whites, and yellow vegetables like squash, but less whole grains and legumes. But here’s the catch: these patterns were only weakly associated with hormone levels. The way people ate explained just 2.5% to 4.1% of the variation in hormone levels. In plain terms? Food didn’t seem to be a major driver of hormonal shifts.
Sable Fest emphasized: “these patterns were characterized by food items or groups that have been previously associated with breast cancer risk, including alcohol, legumes, and whole grains, which may also impact breast cancer risk through inflammatory or metabolic pathways.”
Something to consider is that alcohol came up again and again in the dietary habits that increased hormone levels. When the researchers removed alcohol from the analysis, the link between diet and breast cancer risk became weaker or disappeared entirely in some cases. This is one more reason to be mindful of alcohol. We already know drinking is a risk factor for breast cancer, and this study suggests that this may be because alcohol appears to affect estrogen metabolism during key phases of the menstrual cycle. That extra estrogen exposure may, over time, tip the scale towards cancer.
But there was one exception: the positive association between premenopausal breast cancer and the low-fiber diet that increased follicular estrone remained even after they removed alcohol from the pattern definition, which means that alcohol wasn’t the driving factor of this association. This finding makes a case for fiber-rich foods—whole grains, beans, lentils, and similar staples. These foods seem to help the body manage and clear excess estrogen, possibly through their effects on the immune system and gut bacteria. Prior research has shown that fiber may slightly lower estrogen levels, and this study adds some weight to that idea.
The researchers emphasized that more work is needed to understand exactly how food interacts with hormones, inflammation, and cancer risk. But one thing we know is that the way we eat matters, even in ways we can’t always see. And that’s a powerful thing to remember the next time we’re planning dinner.
This research was supported by the National Institutes of Health and the Breast Cancer Research Foundation.
Fred Hutch/University of Washington/Seattle Children's Cancer Consortium member Dr. Holly Harris contributed to this work.
Fest, S. N., Farland, L. V., Doody, D. R., Eliassen, A. H., Rosner, B. A., Fung, T. T., Hankinson, S. E., Kensler, T. W., Willett, W. C., & Harris, H. R. (2025). Hormone-associated dietary patterns and premenopausal breast cancer risk. Breast cancer research and treatment, 10.1007/s10549-025-07689-4. Advance online publication.
Science Spotlight writer Darya Moosavi is a postdoctoral research fellow within Johanna Lampe's research group at Fred Hutch. Darya studies the nuanced connections between diet, gut epithelium, and gut microbiome in relation to colorectal cancer using high-dimensional approaches.
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