Originally published by 2 Minute Medicine® (view original article). Reused on AccessMedicine with permission.

1. Very-low-calorie diet significantly altered composition of the gut microbiome in study participants, including an enrichment in pathogenic Clostridiodies difficile.

2. Stool samples from post-diet patients similarly induced weight loss in mice due to impaired nutrient absorption and enrichment in Clostridiodies difficile.

Evidence Rating Level: 1 (Excellent)

The gut microbiome plays an important role in health and disease and is greatly modulated by components and patterns of our diet. However, how our diet patterns, especially in the scenario of severe caloric restriction, affect our gut microbiome is poorly understood. This randomized control trial assessed the effects of severe caloric restriction on number, composition, and function of gut microbiome. 80 post-menopausal women who were overweight were randomized to either diet or stable weight control group for 16 weeks. Participants in the diet group consumed shakes with less than 800 calories a day.

Overall, dieting reduced the number of microorganisms present in the gut, diversity of the composition of gut microbiome, and number of metabolites produced by gut microbiota. To directly test whether gut microbiome alone can contribute to weight loss, stool samples from participants pre and after diet were transplanted into mice lacking gut microbiome. Mice receiving post-diet stool samples had rapid and sustained weight loss and decreased body fat. However, weight loss was found to be in part due to decreased efficiency of dietary energy intake and enrichment in Clostridioides difficile, a pathogenic bacterial strain that can cause severe colitis. This study was limited in the homogeneity of its patient population and the type of food supplied as part of the diet. Furthermore, this study did not assess how long after dieting observed changes could be sustained. Nonetheless, this study points to further need to better understand the interaction between diet, acute changes in diet pattern, and gut microbiome in health and disease.

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