Weight loss: Fasting may improve gut microbiome in some people

Last Updated : 2024-12-23

A collage of analog clocks and a woman eating a salad

Fasting may have a significant impact on gut bacteria, a new study shows. Design by MNT; Photography by d3sign/Getty Images & Emmanuel Faure/Getty Images

Evidence is building that a healthy, diverse gut microbiome can benefit health.
Studies have shown that people and animals with obesity often have a less diverse microbiome than those of a healthy weight.
Now, research from China suggests that intermittent energy restriction (IER) — which involves eating normally on some days and eating a very restricted diet, or fasting, on others — not only helps people lose weight but may also alter their microbiome.
This small, observational study shows only an association between weight loss and microbiome changes, rather than any causative effects.

Recently, research has found increasing evidence of the potential effects of the human microbiome on our health.

The microbiome consists of bacteria, archaea, viruses and eukaryotic microbes that live in and on our bodies. A healthy adult will house around 1000 different species of bacteria, the majority of which are in the gut.

In most people, the core microbiota remain stable throughout adulthood, but the gut microbiota differs between different people. It is affected by body mass index (BMI) level, exercise frequency, lifestyle, cultural and dietary habits, and antibiotic use.

Studies in people with obesity have found that they tend to have a less diverse gut microbiome, and the balance of species is different from that of leaner people. Other studies have suggested that the ease with which people lose weight on diets is linked to the composition of their gut microbiome. However, research has not yet revealed a consistent association between gut microbiota and obesity.

A meta-analysis of studies found that weight loss was associated with an increase in microbiome diversity and a reduction in intestinal permeability.

Now, a small study from China has suggested that intermittent energy restriction (IER), as well as helping people with obesity to lose weight, may alter their gut microbiota.

The study is published in Frontiers in Cellular and Infection Microbiology.

The types of gut bacteria affected by weight loss

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.

How gut bacteria changes affect health

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.