Data from a randomized-controlled trial that compared meat eaters to meat-and-berry eaters found that fecal samples from berry eaters had higher amounts of protective nutrients that reduced the viability of cancer cells.
Writing in The Journal of Nutritional Biochemistry, scientists from the Human Microbiome Research Program and the Department of Food and Nutrition at the University of Helsinki concluded that berries may protect against colorectal cancer development.
“The difference seen in gut metabolism was probably induced by the higher intakes of dietary fiber, vitamins C and E, manganese and polyphenols by the berry diet,” they noted
Mitigating the detrimental effects of red and processed meat
In 2015, the World Health Organization (WHO) classified processed meat as carcinogenic to humans and red meat as “probably carcinogenic” based on limited studies. It advised that the consumption of red and processed meat is associated with colorectal, pancreatic and prostate cancer.
The colon’s lining constantly interacts with compounds and metabolites from food. In the aqueous phase of feces, the solid compounds in fecal water “are most likely to directly interact with the dividing epithelial cells at the bottom of colonic crypts,” the current researchers noted, adding that some of these compounds may induce or promote cancer.
In their study, the key microbiota alterations included diminished amounts of beneficial bacteria that produce butyrate and protect the gut lining.
The researchers noted that their findings are consistent with previous research demonstrating that meat-rich diets are associated with a microbial composition that can lead to inflammation and impaired gut health. This may be partly due to the prolonged transit time and fecal pH associated with dietary meat, leading to detrimental effects on gut bacteria.
The addition of berries to the meat diet “seemed to correct unfavorable microbiota changes by increasing the insoluble fiber intake and/or the intake of polyphenols,” they noted.
Study details
The study was a randomized controlled trial lasting four weeks that included 43 healthy adults assigned to one of two groups. The meat group consumed 150 g of red and processed pork meat daily, and the meat and berries group consumed the same quantity of red and processed meat plus 200 g of mixed berries.
The berry mixture included strawberry, raspberry, cloudberry, lingonberry, bilberry and blackcurrant. The daily meat portion reflected the level consumed in Western diets.
Researchers analyzed fecal samples and three-day food diaries at baseline and after four weeks.
The results found no significant differences in the two groups’ overall diversity and abundance of gut microbiota. However, within-group analyses showed that “the relative abundances of beneficial Roseburia and Faecalibacterium were decreased and an unclassified group of Peptostreptococcaceae increased significantly in the Meat group."
The researchers also conducted an in vitro assessment of the viability of cancer cells to fecal water in both groups. They reported that the berry group showed increased phenolic metabolites and reduced viability compared to the meat-only group. P-coumaric acid was particularly noted as being inversely associated with malignant cells.
Source: The Journal of Nutritional Biochemistry. doi: 10.1016/j.jnutbio.2025.109906. “Berry supplementation in healthy volunteers modulates gut microbiota, increases fecal polyphenol metabolites and reduces viability of colon cancer cells exposed to fecal water—a randomized controlled trial”. Authors: T. Onali et al.