INTRODUCTION: Obesity has become one of the most common chronic conditions, causing a large number of comorbidities. During the last decades, a growing number of studies have associated obesity with altered microbiome composition. Moreover, numerous studies reported the effects of diet- and surgery-induced weight loss on the microbiome. This narrative review aims to give an overview of studies published between 2021 and early 2022 about the microbiome in obesity.

MATERIAL AND METHODS: A literature search using the search term ‘Obesity AND (Microbiota OR Microbiome)’ was conducted in Medline. Only research studies in humans published between March 2021 and March 2022 were eligible for inclusion.

RESULTS: Out of 1877 studies, 69 discussed the microbiome composition in obesity or reported how weight loss by a diet or bariatric surgery influenced the microbiome. In general, obesity is associated with the upregulation of the Firmicutes phylum compared to the Bacteroidetes phylum. However, the microbiome is also modified due to changes at all levels of the microbiome. No studies were able to unravel a causal link between certain microbial patterns and the development of obesity. The intestinal microbiome in obesity was affected by genetic, environmental, and phenotypic factors. Similarly, weight loss was also associated with extensive modifications of the gut microbiome. More changes in the microbiome were seen after bariatric surgery compared to diet-induced weight loss.

CONCLUSIONS: Although a large number of studies have demonstrated that obesity and weight loss modify the intestinal microbiome, it is unclear how these changes occur. Future studies should focus on the mechanisms by which the microbiome interacts with the metabolism in obesity.