Gut microbes display circadian rhythmicity, and extended fasting periods are required for the performance of repair functions in the intestinal mucosa by these microbes.

Study: Nfil3 integrates circadian rhythm and microbial metabolite signaling to maintain gut–liver immune–metabolic homeostasis under high-fat diet stress

The study shows that gut bacteria work in sync with our body’s daily clock and help repair the gut lining when things get out of balance — like when eating too much junk food. It doesn’t test fasting directly, but it shows that keeping bacteria healthy helps the gut heal.

Study: Dapagliflozin-intermittent fasting combination maximizes weight and metabolic regulation through AMPK/sirtuins/clock genes and gut microbiota signaling in high-fat diet-induced obesity: a novel anti-obesity approach

The study found that when rats went without food for long periods (16 hours a day), their gut bacteria became healthier and their internal body clocks slowed down in a way that suggests repair was happening — just like the claim says.

Study: The importance of meal timing for maintenance of daily rhythms in the gut transcriptome and microbiota

When mice ate constantly, their gut bacteria lost their daily schedule and stopped producing important healing chemicals. This suggests that giving the gut a break with fasting helps the bacteria do their repair work.

Study: Daytime restricted feeding Promotes Circadian Desynchrony and Metabolic Disruption with Changes in Bile Acids profiles and Gut Microbiota in C57BL/6 Male Mice.

When mice ate during the day instead of at night, their gut bacteria got out of sync and became less healthy. This suggests that gut bacteria need a long break from food (like overnight fasting) to do their repair work properly.