Sleep loss caused a 20% decrease in insulin sensitivity and changes in the gut microbiome in a small pilot trial in humans.

The decreased insulin sensitivity was, however, unrelated to alterations in gut microbiota following sleep loss.

The study involved restricting sleep to ~4 hours per night for two consecutive days. The sleep loss caused a composition change in the gut microbiome including an increased ratio of Firmicutes to Bacteroidetes (which parallel the gut microbiome of obese subjects compared with normal-weight subjects).