A claim you hear on longevity podcasts

Does low butyrate raise breast cancer risk?

Leaning for. Of 9 studies that test it, 7 partly agree, 1 agrees and 1 disagrees.

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The claim checked: Women with low butyrate have a higher risk of breast cancer Hear it at 26:40

What do the studies say?

Leaning for

Butyrate is a fatty acid made by gut bacteria when they break down fiber. Only one of nine studies agrees, and it was small: 12 women with breast cancer had less butyrate in their stool than 12 healthy women. One disagrees: in Malaga, butyrate levels did not differ. Seven are mixed. Most count the gut bacteria that make butyrate, not butyrate itself, and find some of them lower and others higher in women with breast cancer. Every study measured women once, at or after diagnosis, so none can show that low butyrate came first.

Computed from 9 studies that test this point, each judged by two readers, in full. 4 more studies are waiting for a full read and do not count yet.

What was said on the podcast?

“So when women have a low level of butyrate, they actually have an increased risk of breast cancer.”
Elizabeth Boham, a guest on The Doctor's Farmacy · It's Not Bad Luck. This Is What Actually Makes Your Body Vulnerable to Breast Cancer · 26:40 on YouTube
Episode check Bioidentical hormone therapy does not cause breast cancer, the episode says. Four studies conflict on it. 6 claims checked against 72 studies · 7 chapters not checked yet See the whole episode →
The point checked Leaning for

Women with low butyrate levels have a higher risk of breast cancer

Agree 1

other primary study · 2024

“The levels of acetate, propionate and butyrate are lower in the faecal samples of BC patients than that in control samples.”

Butyrate inhibits the malignant biological behaviors of breast cancer cells by facilitating cuproptosis-associated gene expression. J Cancer Res Clin Oncol
Who: 12 surgically treated breast cancer patients and 12 healthy volunteers (faecal SCFA) at a hospital in Nanchang, China; plus T47D/MCF-7 cell lines and 18 female nude mice with T47D xenografts
PMID 38833016

Partly agree 7

other primary study · 2018 · landmark

“Fourteen butyrate-synthesis genes were found: 10 genes were enriched in controls and 4 genes were enriched in postmenopausal patients ( q value < 0.05, Wilcoxon rank sum test; Additional file 1 : Table S11).”

Breast cancer in postmenopausal women is associated with an altered gut metagenome. Microbiome
Who: Untreated breast cancer patients and healthy controls at Guangxi Medical University hospitals, China: 18 premenopausal patients, 25 premenopausal controls, 44 postmenopausal patients, 46 postmenopausal controls
PMID 30081953

trial or observed group · 2021

“It is too early to hypothesize that the suggested decrease in Bifidobacterium , Coprococcus , Butyricimonas, and Odoribacter genera observed in our BC patients at an early stage of their disease might be linked to a role of these bacteria in the development of their cancer.”

Faecal Microbiota Composition Varies between Patients with Breast Cancer and Healthy Women: A Comparative Case-Control Study. Nutrients
Who: 25 women with early-stage ER/Pg-positive, HER2-negative breast cancer before any therapy and 30 healthy control women, ICO René Gauducheau, Saint-Herblain, France
PMID 34444865

other primary study · 2021

“Furthermore, some species within our breast disease-associated taxa (e.g., Bacteroides, Dialister, Coprococcus, Faecalibacterium, Pseudobutyrivibrio, and Romboutsia) are thought to be involved in short chain fatty acid metabolism, which in turn affects gut barrier integrity and systemic inflammation (35–37).”

Associations of fecal microbial profiles with breast cancer and nonmalignant breast disease in the Ghana Breast Health Study. Int J Cancer
Who: Ghanaian women aged 18-74 in the Ghana Breast Health Study (three hospitals in Accra and Kumasi): 379 breast cancer cases, 102 non-malignant breast disease cases, 414 population-based controls
PMID 33460452

other primary study · 2023

“Overall, there are more SCFA-producing bacteria significantly depleted in our BC cohort than those enriched.”

Breast cancer patients from the Midwest region of the United States have reduced levels of short-chain fatty acid-producing gut bacteria. Sci Rep
Who: White women in Iowa: 22 invasive breast cancer patients (mostly postmenopausal, 18 HR-positive, 22 on hormonal therapy, after chemotherapy/radiation) from the University of Iowa BMER and 19 healthy controls
PMID 36631533

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other primary study · 2024

“An increase in the concentrations of five other SCFAs (acetic, propanoic, isobutyric, butanoic and pentanoic acids) and three AAs (Ala, Gly, and Pro) was detected in fecal samples from patients with breast cancer and CRC.”

Microbial and Metabolic Gut Profiling across Seven Malignancies Identifies Fecal Faecalibacillus intestinalis and Formic Acid as Commonly Altered in Cancer Patients. Int J Mol Sci
Who: Patients with seven malignancies (including breast cancer) recruited 2018-2022 at the Maria Sklodowska-Curie National Research Institute of Oncology, Poland, with sex- and age-matched healthy controls
PMID 39125593

other primary study · 2024

“Based on the IVW method, in the East Asian population, Porphyromonadaceae had an inversely association with breast cancer risk, with an OR of 0.304 (95% CI 0.155–0.596, FDR = 0.0005), and Ruminococcaceae also showed an inversely association with breast cancer risk, with an OR of 0.674 (95% CI 0.508–0.895, FDR = 0.03173).”

Exploring the relationship between gut microbiota and breast cancer risk in European and East Asian populations using Mendelian randomization. BMC Cancer
Who: Two-sample Mendelian randomization: gut microbiome GWAS from MiBioGen (18,340 samples, 24 populations) against breast cancer GWAS from FinnGen R10 (Europeans) and Biobank Japan (East Asians)
PMID 39118079

other primary study · 2026

“According to the summary plot, bacterial genera such as Bacteroides , Lachnoclostridium , Parasutterella , Tannerellaceae , Flavonifractor , Bilophila , Subdoligranulum , Faecalibacterium , and Blautia were identified as having a positive association with breast cancer, implying a higher abundance of these genera tends to contribute to increased BC risk.”

Identification of Key Microbial Signatures Associated With Breast Cancer: Machine Learning-Based Approaches Using Gut Microbiome Data. Cancer Med
Who: Secondary machine-learning analysis of public 16S rRNA stool data from the Ghana Breast Health Study: 520 Ghanaian women with breast cancer and 442 healthy controls
PMID 42226580

Disagree 1

other primary study · 2025

“No significant differences were found in the fecal levels of propionic acid (PA) ( p = 0.17), butyric acid (BA) ( p = 0.59), or valeric acid (VA) ( p = 0.40) between the study groups.”

Exploring the Interplay Between Gut Microbiota and the Melatonergic Pathway in Hormone Receptor-Positive Breast Cancer. Int J Mol Sci
Who: Cross-sectional, single-center study in Malaga: 76 women with primary ER-positive stage I-III breast cancer (56 HR+HER2-, 20 HR+HER2+) and 16 healthy women, aged 44-85, mostly postmenopausal
PMID 40725047

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