‘Slimming’ significantly alters your microbiome and brain activity

Weight loss via intermittent energy restriction (IER) results in changes in the brain and in the gut, according to scientists in China. IER involves days of relative fasting alternate with days of eating normally to reduce overweight and obesity. It appears to do this by affecting people’s appetite and parts of the brain involved in addiction.

‘Here we show that an IER diet changes the human brain-gut-microbiome axis,’ said Dr Qiang Zeng, a researcher at the Health Management Institute of the PLA General Hospital in Beijing. ‘The observed changes in the gut microbiome, and in the activity in addiction-related brain regions during and after weight loss, are highly dynamic and coupled over time.’

The authors examined stool samples, blood measurements, and functional magnetic resonance imaging (fMRI) to study changes in the composition of the gut microbiome, physiological parameters and serum composition, and brain activity in 25 obese Chinese women and men on an IER diet. Participants were on average 27 years old, with a BMI between 28 and 45.

‘A healthy, balanced gut microbiome is critical for energy homeostasis and maintaining normal weight. In contrast, an abnormal gut microbiome can change our eating behaviour by affecting certain brain area involved in addiction,’ explained coauthor Dr Yongli Li from the Department of Health Management of Henan Provincial People’s Hospital in Henan, China.

Participants underwent a ‘high-controlled fasting phase’ of 32 days where they received personalised meals with a caloric value decreasing stepwise to one quarter of their basic energy intake. They then spent 30 days in a ‘low-controlled fasting phase’, where they were given a list of recommended foods: participants who adhered perfectly to this diet would receive 500 calories per day for women and 600 calories per day for men.

By the end of the study, their body weight had decreased by an average of 7.6kg, or 7.8%. As expected, they had undergone reductions in body fat and waist circumference.

Likewise, their blood pressure and serum levels of fasting plasma glucose, total cholesterol, HDL and LDL had decreased, along with the activity of key liver enzymes. These suggest that IER helps to reduce obesity-related comorbidities like hypertension, hyperlipidaemia, and liver dysfunction.

The authors observed decreases after IER in the activity of brain regions implicated in the regulation of appetite and addiction. Within the gut microbiome, the abundance of the bacteria Faecalibacterium prausnitzii, Parabacteroides distasonis, and Bacterokles uniformis increased sharply, while that of Escherichia coli fell.

Further analyses showed that the abundance of E. coli, Coprococcus comes, and Eubacterium hallii bacteria were negatively associated with the activity of the brain’s left orbital inferior frontal gyrus – known to play a key role in executive function, including our will to lose weight. In contrast, the abundance of the bacteria P. distasonis and Flavonifractor plautii were positively correlated with the activity brain regions associated with attention, motor inhibition, emotion, and learning.

These results suggest that changes in the brain and microbiome during and after weight loss are linked – either because they cause each other, or because an unknown other factor causes both.

‘The gut microbiome is thought to communicate with the brain in a complex, two-directional way,’ explained Dr Xiaoning Wang from the Institute of Geriatrics of the PLA General Hospital. ‘The microbiome produces neurotransmitters and neurotoxins which access the brain through nerves and the blood circulation. In return the brain controls eating behaviour, while nutrients from our diet change the composition of the gut microbiome.’

The researchers are now exploring the precise mechanism by which the gut microbiome and the brain communicate in obese people, including during weight loss.