Intermittent fasting altered the microbiome and brain activity

Interval (or periodic) fasting helps not only to lose extra pounds, but also to change the axis "human brain - intestine - microbiome". Chinese scientists have come to this conclusion.

More than one billion people in the world suffer from obesity. It is considered a risk factor for cardiovascular disease, diabetes and some cancers. But losing weight permanently is not easy: complex interactions between body systems, such as hormones and the brain, are known to often work against it. 

One popular weight loss method is intermittent energy restriction (IER, interval fasting). This is a medical practice of establishing and strictly adhering to a schedule of food intake with periods of complete avoidance (or severe reductions in kilocalorie intake) followed by periods of unrestricted consumption. Previously, scientists have found that this approach not only helps to get rid of excess weight, but also reduces blood pressure, the intensity of inflammatory processes and the risk of heart disease.

Now Chinese experts have decided to test how the IER method acts on the gut microbiome and brain activity. The results are published in the journal Frontiers in Cellular and Infection Microbiology. 

Twenty-five obese Chinese residents participated in the study. The average age was 27 years and their body mass index (BMI) ranged from 28 to 45.

The authors studied changes in the composition of the gut microbiome (by metagenomic analysis), physiologic parameters and serum composition, and brain activity of the participants (by functional magnetic resonance imaging.

First, they underwent a "strictly controlled fasting phase". For 32 days, the participants received individualized meals designed by a nutritionist. Caloric intake was gradually reduced to one-quarter of their basal energy intake. 

The subjects then spent 30 days in a "low-control fasting phase." During this period, participants were given a list of recommended foods. In an ideal diet, women received 500 kilocalories per day and men received 600 kilocalories.

By the end of the study, the participants' body weight had decreased by an average of 7.6 kilograms, or 7.8%. As expected, their body fat and waist circumference decreased.

Similarly, blood pressure and levels of fasting plasma glucose, total cholesterol, high and low density lipoproteins, and the activity of key liver enzymes decreased. According to the scientists, this proves that interval fasting helps reduce the risk of obesity-related comorbidities such as hypertension, hyperlipidemia and liver dysfunction.

In addition, the participants showed a decrease in the activity of brain regions involved in the regulation of appetite and addiction. And the number of Faecalibacterium prausnitzii, Parabacteroides distasonis and Bacterokles uniformis bacteria sharply increased in the gut microbiome. The abundance of Escherichia coli decreased.

Further analyses showed that the abundance of E. coli, Coprococcus and Eubacterium hallii bacteria was negatively associated with the activity of the left orbital inferior frontal gyrus of the brain, which plays a key role in executive functions including the desire to lose weight. In contrast, the abundance of P. distasonis and Flavonifractor plautii bacteria was positively correlated with the activity of brain regions associated with attention, motor inhibition, emotion and learning.

The authors concluded that changes in the brain and microbiome during and after weight loss are related. However, because the study is a correlational study, the researchers were unable to determine the direction of the underlying causation.

"The gut microbiome is thought to interact with the brain in a complex, bidirectional, way. The microbiome produces neurotransmitters and neurotoxins that reach the brain via nerves and blood flow. In turn, the brain controls eating behavior, and nutrients from our diet can alter the composition of the gut microbiome," the scientists concluded.