The research, conducted at the Faculty of Physical Education and Sport at Comenius University in Bratislava and published in the journal Cancer Reports, is described by its authors as the first human study to examine the combined effects of physical activity and dietary intervention on the gut microbiome in breast cancer patients. It unfolded in two parts: a cross-sectional observational comparison of gut bacteria among three groups of women, and a randomized controlled trial testing the dance-and-diet intervention in breast cancer patients with obesity. The trial is registered as a clinical trial under number NCT07213271.

The observational component included 23 breast cancer patients with obesity in remission, with a mean body mass index of 32.43 kg/m², alongside 16 women with obesity but no cancer history (mean BMI 37.78 kg/m²) and 16 healthy controls (mean BMI 21.26 kg/m²). Stool samples were analyzed using sequencing of the V3–V4 region of the 16S rRNA gene, a standard technique that profiles bacterial communities by reading a stretch of DNA found in all bacteria. Reads were classified to the species level using the CLARK algorithm and reference databases built from SILVA and UNITE sequences. Alpha diversity, which measures the number and evenness of species within a single individual, was estimated with the Shannon and Chao1 indices, while beta diversity, which captures differences in community composition between individuals, was calculated using Bray–Curtis dissimilarity and tested with permutational multivariate analysis of variance.

The results were unambiguous. Healthy women had significantly higher Shannon diversity and Chao1 richness than either of the two groups with obesity, but the deeper story emerged in the compositional data. Breast cancer patients differed significantly in beta diversity from both control groups at every taxonomic level examined, from phylum to species, while the two control groups did not differ from each other at all. Group membership explained between roughly 8 and 12 percent of the variance in microbial composition. At the phylum level, breast cancer patients had significantly lower relative abundance of Bacteroidetes and higher abundance of Firmicutes compared with both controls. Perhaps most striking was Faecalibacterium prausnitzii, a health-associated, butyrate-producing bacterium that has been shown in laboratory studies to suppress the proliferation and invasion of breast cancer cells and to promote apoptosis. Its abundance was significantly lower in breast cancer patients with obesity than in the non-cancer controls with obesity, and Phocaeicola vulgatus, another beneficial species, was reduced compared with both control groups.

These findings matter because they suggest that something about the cancer itself, or its treatment, reshapes the gut ecosystem beyond what obesity alone explains. Previous studies had reported reduced microbial diversity in breast cancer patients and in people with obesity, but most comparisons had been made against normal-weight controls. By including a non-cancer control group with obesity, the Slovak team was able to separate the microbial signature associated with excess weight from the signature associated with cancer and its treatment — and the latter proved distinct. The authors note that cancer-related factors, including treatment exposures, may contribute to a compositional restructuring of the gut microbiome that obesity alone does not produce.

The interventional arm then asked whether lifestyle change could move this altered ecosystem. Forty breast cancer patients with obesity in remission were recruited between April and June 2025, and those who completed the study were randomly assigned either to a 12-week intervention or to a non-intervention control group. In the end, 13 women in the intervention group completed the program with at least 80 percent attendance at dance classes, and 10 women completed the study as controls. The dance program was demanding and structured: supervised sessions three times per week, each lasting 60 minutes, taught by certified professional dancers and incorporating choreographies from folkloric, Latin American, and contemporary genres. Alongside the dancing, participants received an individualized nutrition plan generated by nutrition software, prescribing 1200 to 1500 kcal per day based on measured resting metabolic rate, with 30 to 50 percent of energy from carbohydrates, 25 to 30 percent from fats, 20 to 30 percent from proteins, and 14 grams of fiber per 1000 kcal.

The physical results were substantial. Women in the intervention group lost an average of 4.04 kg of body weight, 1.45 units of BMI, and 3.29 kg of fat mass, with significant reductions also seen in visceral fat, waist and hip circumference, and the waist-to-hip ratio. Effect sizes for these changes were large. Metabolic markers improved in parallel: gamma-glutamyl transferase, a liver enzyme linked to metabolic dysfunction, fell significantly, and HOMA-IR, a mathematical index of insulin resistance calculated from fasting glucose and insulin, dropped from 2.06 to 1.70. The control group showed none of these changes. Cardiorespiratory fitness, measured with an incremental bicycle ergometer test to volitional exhaustion, rose by 3.3 mL/kg/min in maximal oxygen uptake, along with significant increases in maximal minute ventilation, maximal respiratory frequency, and maximal workload. Muscular performance improved as well, with gains in handgrip strength in the right hand, the 30-second arm curl test, and the 30-second chair stand test. The authors note that these fitness gains are clinically relevant, because physical function has been shown to predict survival in breast cancer patients.

Quality of life, measured with the internationally validated EORTC QLQ-C30 questionnaire and its breast cancer-specific BR23 module, told an equally compelling story. Within the intervention group, role functioning, fatigue, and body image all improved significantly. Compared with controls after treatment, the intervention group showed better role, emotional, and social functioning, less fatigue and pain, and fewer systemic treatment-related side effects, with improvements ranging from roughly 16 to 47 percent. Fatigue and pain are among the symptoms that most heavily burden survivors’ lives after cancer treatment, and the authors highlight the improvement in body image, which they suggest may have been fostered by the group-based nature of the dance classes, with their built-in social interaction and peer support.

The microbiome itself changed in subtler but intriguing ways. Total alpha diversity did not shift significantly in the intervention group, although it actually decreased in the controls, a decline the authors attribute possibly to natural temporal or seasonal variation. But the overall community composition diverged between the groups: beta diversity at the phylum level differed significantly between the post-intervention intervention and control groups, with a statistically significant pairwise difference and a modest proportion of variance explained by group membership. Within the intervention group, the abundance of Firmicutes decreased significantly, a shift the authors interpret as potentially favorable given that alterations in the Firmicutes-to-Bacteroidetes balance are frequently associated with metabolic regulation and obesity-related phenotypes. More specifically, two recognized beneficial species, Bifidobacterium pseudocatenulatum and Bifidobacterium animalis, increased significantly, while Klebsiella oxytoca, an opportunistic pathogen linked to cancer cachexia and inflammatory conditions, declined significantly. Members of Bifidobacterium are known to modulate host immune function and produce short-chain fatty acids that support gut barrier function.

One finding ran against expectations: the abundance of butyrate-producing bacteria, including Ruminococcus bromii and Ruminiclostridium hungatei, decreased significantly in the intervention group. These species contribute to resistant starch degradation and short-chain fatty acid production, so their decline contrasts with what might be predicted from a beneficial lifestyle intervention. The authors caution that this could reflect a specific ecological response to the combined intervention, or simply a chance finding arising from the many statistical comparisons made in a small pilot study, and they call for future work with metabolomics to determine whether total butyrate production was actually affected. Meanwhile, measurements of gut permeability, using serum zonulin as a proxy marker, showed a non-significant decreasing trend in the intervention group but a significant increase in the controls. Changes in zonulin were negatively correlated with beneficial bacteria such as Anaerobutyricum hallii, Bifidobacterium breve, and Streptococcus thermophilus, and positively correlated with potentially pathogenic groups including Proteobacteria — an expansion of which is commonly considered a hallmark of dysbiosis — and Neisseria.

The authors are candid about the study’s limitations. Combining dance and diet means the independent contribution of each component cannot be disentangled; a higher-than-expected dropout rate reduced the final sample size and statistical power; and 16S rRNA sequencing offers limited taxonomic resolution and no direct functional insight compared with whole-genome shotgun metagenomics. The p-values reported are unadjusted and exploratory in nature. Still, the trial’s breadth is unusual, spanning stool analysis, blood biochemistry, body composition, cardiopulmonary exercise testing, motor performance, dietary records, and validated quality-of-life questionnaires, and its inclusion of an obesity-matched non-cancer control group addresses a gap left by most prior microbiome studies in oncology.

The broader implications are considerable. Breast cancer is projected to rise from the 22nd to the 16th leading cause of death globally, with annual deaths expected to grow from 0.82 million in 2022 to 1.16 million by 2050, even as survival rates continue to improve — meaning more women than ever will live with the long-term consequences of treatment. Obesity in this population is consistently associated with increased risk of recurrence and worse overall survival, making interventions that simultaneously address weight, fitness, insulin sensitivity, and psychological well-being especially valuable. The image of middle-aged cancer survivors improving their VO2max and shrinking their visceral fat through folkloric and Latin dance is an appealing one, and the parallel microbial shifts — more Bifidobacterium, fewer Klebsiella — hint that the benefits of joyful movement may extend all the way down to the gut ecosystem. Larger, adequately powered trials with diet-only control groups and metagenomic sequencing, the authors conclude, are now needed to clarify the specific role of physical activity in shaping the microbiome during breast cancer survivorship.

The experiment was designed to model the consequences of prolonged dietary stress rather than the short, simplified feeding periods often used in laboratory obesity research. Male C57BL/6 mice, a strain commonly used in metabolic studies, consumed a high-fat diet for 44 weeks. The animals were then divided into four groups for an additional eight weeks. One group continued eating the high-fat diet without exercise, while a second continued the diet but ran on a treadmill. Two other groups switched to a normal diet, either remaining sedentary or adding treadmill exercise. The exercise protocol involved running at 18 metres per minute for 50 minutes per session, five days each week. In total, 26 mice entered the study, although the continued high-fat, sedentary group began with eight animals and ended with five after three deaths. The other intervention groups each had six surviving animals, making the results informative but relatively small and exploratory.

The long-term high-fat diet produced a broad syndrome of metabolic and tissue deterioration. The mice became progressively obese, developed impaired glucose tolerance and experienced shortening of the colon, a physical change that can accompany intestinal stress and inflammation in experimental disease models. In the sedentary group that remained on the high-fat diet, two animals also developed macroscopic tumours visible during examination. The authors describe that observation as exploratory rather than evidence that the diet caused cancer. No deaths or macroscopic tumours were reported in the three intervention groups, and survival was 62.5 per cent in the sedentary high-fat group compared with 100 per cent in the other groups. A log-rank statistical test indicated a difference in survival between groups, with a reported p value of 0.0053. Because the number of animals was small and the tumour finding was not the primary endpoint, the observation should not be interpreted as a direct prediction of cancer risk in humans.

The dietary reversal nevertheless produced striking short-term changes in body weight. After eight weeks, sedentary mice that switched to normal food lost an average of 2.93 grams, while those that both changed diet and exercised lost 7.03 grams. By contrast, sedentary mice that continued the high-fat diet gained 0.39 grams. The reversal groups also performed better on an oral glucose-tolerance test, which measures how efficiently the body clears a measured dose of glucose from the bloodstream. Improved glucose tolerance generally indicates better coordination among insulin secretion, liver glucose handling, muscle uptake and other metabolic processes. The results suggest that at least some consequences of long-term high-fat feeding remained responsive to a relatively brief intervention. Exercise added another benefit: when paired with dietary reversal, it preserved bone mineral density and bone mineral content, outcomes that can be affected by altered body composition and prolonged metabolic dysfunction.

The researchers focused particularly on macrophages, immune cells that reside in adipose tissue and respond to signals from damaged, stressed or expanding fat depots. In obesity, adipose-tissue macrophages can accumulate around dying fat cells and adopt inflammatory programs that release signalling molecules capable of interfering with insulin action. Scientists often describe these cells using an M1/M2 framework, with M1-like macrophages considered more inflammatory and M2-like cells associated with repair and immune regulation. That framework is useful but biologically imperfect: macrophages exist along a spectrum of states, and their behaviour depends on local signals rather than a simple two-category switch. In this study, the surface marker CD86 appeared more responsive to the interventions than CD11c, another marker frequently used to identify inflammatory adipose macrophages. The CD86-based M1/M2 ratio fell to 1.05 ± 0.48 in sedentary mice that changed diet and to 1.06 ± 0.46 in mice receiving both interventions, compared with 1.97 ± 0.72 in sedentary animals that stayed on the high-fat diet.

CD86 is a protein displayed on the surface of antigen-presenting immune cells, where it helps provide the co-stimulatory signals needed to activate T cells. Its presence on macrophages can therefore indicate a cell that is prepared to engage more actively with adaptive immunity, although it is not a complete measure of inflammatory function by itself. The study’s finding that CD86, rather than CD11c, more sensitively tracked the intervention response suggests that marker choice can substantially influence how researchers interpret adipose inflammation. The lower CD86-based ratio after diet reversal is consistent with a shift away from a strongly activated immune environment, but it does not prove that macrophages alone drove the metabolic recovery. Changes in fat-cell size, insulin sensitivity, circulating hormones, intestinal permeability and other immune populations may also have contributed. The result is best understood as a molecular signature accompanying improvement rather than a single switch that explains it.

To examine the microbial side of the system, the team used long-read 16S ribosomal RNA sequencing. The 16S rRNA gene contains variable regions that differ among bacterial lineages, allowing researchers to identify and compare members of the gut community. Long-read sequencing can capture a larger portion of that gene than many short-read approaches, potentially improving taxonomic resolution, although it still does not reveal every function a microorganism performs. After dietary reversal, the mice showed improved microbial diversity and community structure, with the most prominent changes in animals that also exercised. The ratio of Firmicutes to Bacteroidota decreased after the diet switch, a result that reached statistical significance with a reported p value of 0.0313. Such broad phylum-level ratios have often been treated as a shorthand for obesity-related microbiome changes, but they can conceal enormous variation among species and should not be used as a universal measure of health.

The most attention-grabbing microbial result involved Faecalibaculum rodentium. Its abundance was strongly correlated with highly activated CD86-positive, CD11c-positive macrophages, producing a correlation coefficient of 0.75 and a p value below 0.001. It also correlated with total CD86-positive macrophages, although more modestly, with an r value of 0.43 and a p value of 0.043. The bacterium was additionally associated with adverse metabolic indices. Meanwhile, Akkermansia and Roseburia increased alongside recovery. These associations are biologically intriguing because gut microbes can influence host physiology through metabolites, cell-wall components and interactions with the intestinal barrier. Short-chain fatty acids produced by some bacteria, for example, can affect epithelial cells and immune signalling. Yet correlation cannot distinguish cause from consequence. A high-fat diet may simultaneously reshape the microbiota, enlarge adipose tissue and activate macrophages, causing all three measurements to move together without any one of them directly controlling the others.

The study therefore points toward a potentially useful way of tracking recovery from diet-induced obesity rather than delivering a ready-made treatment for humans. Its design combined two practical lifestyle variables—food composition and physical activity—and showed that changing diet was associated with rapid metabolic improvement even after 44 weeks of high-fat exposure. Adding exercise appeared to strengthen microbiome recovery and protect bone measures, while the immune analysis highlighted CD86 as a candidate marker for intervention-responsive adipose inflammation. Still, the work involved only male mice, and the groups were small. Mouse diets, gut communities, activity patterns and immune systems differ from those of humans, and treadmill running is more controlled than ordinary human exercise. The study also measured associations over a limited eight-week period and did not establish which microbial or immune changes occurred first. Future research will need to test whether the CD86–Faecalibaculum relationship appears in people, whether it predicts metabolic improvement and whether manipulating the microbiota can alter inflammation independently of weight loss. For now, the message is both hopeful and cautious: even after prolonged high-fat feeding, the immune and microbial ecosystems surrounding fat tissue may remain capable of meaningful change when diet and movement change together.