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The Role of Gut Microbes in Weight Loss

7 August 2023by Barış Özdinç

Losing weight is a burden for many while it may emerge as the simplest thing for others. A recent article published in the Washington Post suggests that the reason may be gut microbiome variation. 

The article highlights a recently published paper in the Nature Communications journal that challenges the notion that all calories contribute equally to weight gain. 

The research suggests that the body responds differently to calories derived from high-fiber whole foods compared to ultra-processed junk foods. The key factor at play is the impact on the gut microbiome, with fiber-rich diets positively affecting weight loss.


Processed foods are quickly absorbed in the upper gastrointestinal tract, leaving fewer calories for the gut microbiome located in the large intestine. In contrast, high-fiber foods are not easily absorbed, allowing them to reach the gut microbiota. 

By consuming a fiber-rich diet, individuals not only nourish themselves but also provide sustenance for their gut microbes. This new research indicates that this phenomenon effectively reduces overall calorie intake. 

To assess the calorie intake from high-fiber whole foods and ultra-processed junk foods, the research group has designed  a clinical trial. In the clinical trial researchers compared the effects of a fiber-rich diet to a diet consisting of highly processed foods. 

Seventeen healthy participants were provided with all meals and closely monitored during the 22-day study. The diets were designed to have similar caloric content, protein, fat, and carbohydrates. 

The fiber-rich diet, named the “microbiome enhancer diet,” included foods with resistant starch such as oats, beans, lentils, chickpeas, brown rice, quinoa, nuts, fruits, and vegetables. It aimed to maximize the nourishment reaching the gut microbiota by avoiding processed, ground, or refined foods.


The study revealed that participants absorbed significantly fewer calories on the fiber-rich diet compared to the processed food diet. On average, they lost 217 calories per day on the fiber-rich diet, with some experiencing up to 400 calories of daily loss. 

To elucidate the sink of calories from high-fiber foods, the study measured undigested food content in stool, bacterial biomass and bacterial metabolites as short-chain fatty acids. 

To compare the bacterial biomass, the study evaluated the copy number of 16S rRNA genes present in the stool samples. According to the findings, the gap in calorie intake between junk food and high-fiber diets were marked in stool as undigested food, bacterial biomass, and short-chain fatty acids. 

The participants on the fiber-rich diet exhibited higher levels of satiety-promoting hormones and experienced slight weight and body fat reduction without increased hunger.

This study provides further evidence of the benefits of a high-fiber diet for weight loss and sheds light on the underlying mechanisms. 

While the findings are promising, more research is needed to examine the applicability of these results to diverse populations, including older adults and individuals with metabolic diseases. 

Nonetheless, the study highlights the potential for targeted dietary interventions that prioritize gut microbiome health to facilitate weight loss. 


To conclude, understanding the role of the gut microbiome in weight management opens new avenues for personalized approaches to weight loss. 

A fiber-rich diet, which nourishes both the individual and their gut microbes, has been shown to reduce caloric absorption and promote metabolic health. With the prevalence of processed foods on the rise globally, prioritizing the gut microbiome through dietary choices holds promise for improved weight management and overall metabolic health.

If you’re looking to carry out your own microbiome research, contact CosmosID today.

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Barış Özdinç

Barış Özdinç analyzes microbiome research with his educational background in genetics and evolution. As a research analyst for CosmosID, he combines metagenomics and data analyses to identify microbial biomarkers in disease cohorts and evaluate microbiome research tools. His work involves curating microbiome data and creating interesting microbiome content for newsletters and blog posts. Barış Özdinç received his bachelor’s degree in genetics and master’s degree in biodiversity, evolution, and conservation from University College London (UCL). Currently, he lives in Istanbul, Turkey, where he lives with his cat, Delight, and mentors female students in their STEM career pursuits.