A recent study within the DIETFITS (Diet Intervention Examining the Factors Interacting with Treatment Success) randomized trial was conducted to study the role of our highly personalized gut microbiota in the interindividual variability in sustained weight-loss success.

In the short term, the gut microbiota is impacted by changes in diet, as seen when shifting to animal-based or plant-based diets, or to diets with different fiber and macronutrient composition. Intervention studies have also found that weight loss through caloric reduction, regardless of diet composition, is associated with changes in the composition of gut microbiota.

In that study, nondiabetic overweight or obese adults were randomized to a healthy low-carbohydrate or to a low-fat diet. The authors found that both diets resulted in changes in the gut microbiota composition at 3 months: the low-carbohydrate arm increased the relative abundance of the Proteobacteria, Bacteroidetes, and Firmicutes phyla, while in the low-fat arm the microbiota decreased its relative abundance of the Actinobacteria and Firmicutes phyla. Nevertheless, those changes returned to baseline levels after six to twelve months, which the authors concluded may demonstrate the resilience of microbiota composition despite maintenance of dietary patterns and body weight.

If that finding is true, the resilience of microbiota could plausibly underlie the phenomenon of weight regain after initial weight loss, which may be regulated by feedback control processes instead of a simple calories in–calories out concept.

Reference: Mueller NT, Zhang M. Diet and long-term weight loss: what can we learn from our gut microbes?. Am J Clin Nutr. [published online ahead of print]