As part of the study, the researchers recruited 25 people with a body mass index (BMI) of between 28kg/m² (classed as overweight) and 45kg/m² (classed as severely obese). None of the participants had any other uncontrolled health conditions.

To start, they ate a regular diet for four days, and the researchers recorded the energy content of this as their baseline daily intake. For the rest of the study, the researchers interspersed the days of regular baseline energy intake with days where the participants had severely restricted energy intake formulated by a clinical dietitian.

The researchers collected the participants’ blood and fecal samples at the beginning, midpoint, and end of phases II (highly-controlled fasting) and phase III (less-controlled fasting) during the two months the study was conducted. They also recorded their body weight, waist circumference, body fat, systolic blood pressure, and diastolic blood pressure at each time point.

During the study, participants lost, on average, 7.8% of their body weight. And at the end of phase II, their gut microbial diversity had increased from the baseline. However, at the end of phase III, there was no significant difference from the start of the study.

There were also some changes in the species making up the gut microbiota, with a decrease in Escherichia coli and an increase in Faecalibacterium prausnitzii, Parabacteroides distasonis, and Bacteroides uniforms.

Kelsey Costa, a registered dietitian and nutrition consultant for the National Coalition on Healthcare, who was not involved in the study, explained how these changes in gut bacteria might affect health:

“F. prausnitzii is one of the most abundant bacteria in the gut and is generally associated with good health and immunity. […] P. distasonis is associated with breaking down carbohydrates and producing useful metabolites. This bacteria is known to thrive in a diet rich in fiber. B. uniformis is known to have anti-inflammatory properties and plays a role in processing complex sugars in our diet.”

“The alteration in gut microbe abundance induced by the diet is potentially beneficial, as these changes could help modulate metabolic and immune processes, though additional research is needed to fully understand the long-term effects,” she added.

The researchers noted that these changes were associated with significant reductions in the activity of brain regions implicated in the regulation of appetite and addiction. However, they do not explain what effect these changes are likely to have on appetite.

In a press release, co-author Dr. Xiaoning Wang from the Institute of Geriatrics of the PLA General Hospital stated:

“The gut microbiome is thought to communicate with the brain in a complex, two-directional way. The microbiome produces neurotransmitters and neurotoxins, which access the brain through nerves and the blood circulation. In return, the brain controls eating behavior, while nutrients from our diet change the composition of the gut microbiome.”

As an observational study, this research cannot show a causal relationship between IER, weight loss, and the gut microbiome, but it does provide more evidence of a link. The researchers suggest that long-term dietary intervention should be used to maintain weight loss and further clarify the relationship between the gut microbiome and the brain, and Costa agreed.

“Future research should aim to address the exact process through which the gut microbiome interacts with the brain in obese individuals, specifically during weight loss, including the identification of crucial gut microbiome components and brain regions that contribute to successful weight loss and maintenance of a healthy weight,” she told MNT.

She also gave general advice about how to look after your microbiome:

“The gut microbiome is a complex ecosystem, and its relationship with obesity is not fully understood. It’s thought that balance and diversity of gut bacteria may be more important than the presence or absence of specific species.”