Effects of intermittent fasting on the gut microbiota

Whether for religious reasons or as part of the fasting trend, intermittent fasting is likely to have an impact on our gut microbiota. Although demonstrated in mice, no study had, until now, been carried out among humans and even less so during Ramadan.


Fasting and its effects on the makeup of the intestinal microbiota have been the subject of very few studies because they are difficult to model. However, since diet is one of the main environmental factors that can shape our gut microbiota, it is not hard to imagine that prolonged food deprivation may change the composition of this microbial community. Accordingly, a team of Turkish researchers carried out a small study with nine Muslim subjects (seven women and two men) who fasted during Ramadan. A pillar of Islam, this age-old practice involves abstaining from food and drink from sunrise to sunset for a period of 29 days. In the study, conducted between 18 June and 16 July 2015, daily fasts lasted 17 hours.

A healthier gut microbiota

At the end of Ramadan, stool samples obtained from the participants showed a higher abundance of the good bacteria Bacteroides fragilis and Akkermansia muciniphila. The latter group makes up 3%-5% of the microbial community in healthy individuals but this proportion is lower for the obese. Conversely, the abundance of other bacteria decreased, although not significantly. Fast also resulted in a reduction in total cholesterol and fasting blood sugar levels, confirming the results of another study. However, the authors did not observe the significant decrease in participants’ BMI* seen in other studies, presumably because of the small number of subjects involved.

Resistance to change

The authors suggest that the improved makeup of the gut microbiota after fasting is due to the resistance of beneficial bacteria species, such as Bacteroides and Akkermansia, to dietary changes. These results are preliminary and require confirmation in larger studies, but they provide a better understanding of the relationship between fasting and the intestinal microbiota.


* BMI = ratio of weight in kg to square of height in sq.m



Özkul C, Yalınay M, Karakan T. Islamic fasting leads to an increased abundance of Akkermansia muciniphila and Bacteroides fragilis group: A preliminary study on intermittent fasting. Turk J Gastroenterol 2019; 30(12): 1030-5.