October 16, 2025, 9:03 am | Read time: 5 minutes
The effects of strength training go far beyond muscle building. It’s known that weight workouts positively impact bone density, metabolism, and brain performance. But possibly also the gut? Research already suggests that endurance training influences the microbiome. Researchers at the University of Tübingen have now investigated whether strength training has similar effects.
Follow the FITBOOK channel on WhatsApp now!
Study Shows Positive Effect of Strength Training on the Gut
The study has only been published as a preprint so far.1 This means the peer-review process, the evaluation by independent colleagues for quality assurance, is still pending. However, the research team at the University of Tübingen already believes, based on their findings, that resistance training–the umbrella term for various types of strength training using resistance–can influence the gut microbiome.
The microbiome, the entirety of gut bacteria, plays a central role in health, affecting metabolism, the immune system, and even aging processes. Besides diet, various lifestyle factors can influence the gut microbiome. Regarding endurance training, this is well-documented–the study authors point this out in their abstract, and FITBOOK has already reported on related research findings.2 Whether strength training has similar effects was previously unclear. Earlier studies on this topic have found few changes. A research team from Tübingen has now examined whether targeted strength training in previously inactive but overall healthy adults causes measurable changes in the composition and diversity of the gut microbiome.
Details of the Study
The study involved 150 previously physically inactive adults. The preprint does not provide details on the recruitment process. It’s conceivable that participants were found through local postings, online portals, or university volunteer registries. Over eight weeks, participants completed a supervised strength training program. The researchers meticulously documented the exercises performed, weights used, and the number of repetitions. Additionally, data on “participation compliance” was collected, indicating whether participants consistently completed all scheduled training sessions.
To determine possible effects on the gut microbiome, researchers analyzed stool samples from participants in the lab. These were provided at set times during the study. Using 16S rRNA gene sequencing–one of the most common methods for studying the gut microbiome–researchers determined the composition and diversity of gut bacteria. Metabolic analyses (metabolomics) were also used to examine the activity of microbes and their metabolic products.
Also interesting: Vitamin B3 may protect against skin cancer
Study Results
In the overall evaluation, scientists initially found no significant changes, neither in terms of bacterial diversity nor in the composition of the gut microbiome. The metabolic profiles of participants, assessed through metabolic products in the gut, also remained stable.
However, closer examination revealed that greater strength gains from training were associated with measurable changes in the microbiome. The participants, known as “high responders,” showed higher beta diversity in microbial communities. Notably, the proportion of certain health-promoting bacteria increased among them. Many of these belonged to the Lachnospiraceae family, generally associated with a healthy gut flora. Specifically, the species Faecalibacterium and Roseburia hominis, known for their anti-inflammatory properties, were more prevalent.
These Medications Alter Gut Flora–Even Years After Use
The Impact of the Gut Microbiome on Aging
Researcher Explains the Study’s Significance to FITBOOK
The authors conclude from their observations that strength training does indeed affect the gut and can positively change the microbiome. This is especially true for individuals who respond strongly in terms of muscle strength. The changes observed are similar to those known from endurance training, suggesting that different forms of exercise can contribute to a healthier gut flora in various ways.
In response to FITBOOK’s inquiry, study author Prof. Sven Nahnsen emphasizes that the observed changes were most likely due to the training itself. While factors like diet, sleep, or stress can influence the microbiome, participants were explicitly asked to keep their eating habits unchanged during the eight weeks. Additionally, researchers documented medication intake and diet to minimize confounding factors. With the relatively large number of participants–around 150 people–the authors hoped to highlight the training effect more clearly.
Limitations
Nevertheless, as mentioned, the study still needs to undergo a standard quality assurance process. And since there is no control group without training, it cannot be definitively stated that the observed changes are solely due to the strength training completed.
Moreover, these are short-term effects–different or more changes might have occurred over a period longer than eight weeks. “Scientifically, it would be of great interest to also track the long-term changes in the microbiome,” admits Professor Nahnsen. However, the team currently sees no possibility for this, partly due to financial and data protection reasons. It is also hardly realistic for participants to maintain their dietary habits over longer periods.
Finally, it should be noted that the participant group–all generally healthy, previously inactive adults–was quite homogeneous. It remains unclear whether strength training also affects the gut of individuals who were already physically active or those with pre-existing conditions. Researchers find it particularly interesting that individuals with significant strength gains also showed pronounced changes in the microbiome. Attempts to predict these “high responders” based on microbiological or physiological characteristics–such as analyses of the initial microbiome and machine learning methods–have not been successful so far. “Our current analyses suggest that in the current cohort, factors like initial ‘fitness level’ and training intensity have a significantly higher predictive value for strength gains than the microbiome.”