Scientists looking to tackle our ongoing obesity crisis have made an important discovery: Intermittent calorie restriction leads to significant changes both in the gut and the brain, which may open up new options for maintaining a healthy weight.

Researchers from China studied 25 volunteers classed as obese over a period of 62 days, during which they took part in an intermittent energy restriction (IER) program – a regime that involves careful control of calorie intake and relative fasting on some days.

Not only did the participants in the study lose weight – 7.6 kilograms (16.8 pounds) or 7.8 percent of their body weight on average – there was also evidence of shifts in the activity of obesity-related regions of the brain, and in the make-up of gut bacteria.

“Here we show that an IER diet changes the human brain-gut-microbiome axis,” said health researcher Qiang Zeng from the Second Medical Center and National Clinical Research Center for Geriatric Diseases in China when the results were published in December 2023.

“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.”

Right now it’s not clear what causes these changes, or whether the gut is influencing the brain or vice versa. However, we do know that the gut and the brain are closely linked, so treating certain regions of the brain could be a way to control food intake.

The changes in brain activity, spotted via functional magnetic resonance imaging (fMRI) scans, were in regions known to be important in the regulation of appetite and addiction – including the inferior frontal orbital gyrus.

What’s more, the gut microbiome changes, analyzed via stool samples and blood measurements, were linked to particular brain regions.

For example, the bacteria Coprococcus comes and Eubacterium hallii were negatively associated with activity in the left inferior frontal orbital gyrus, an area involved in executive function, including our willpower when it comes to food intake.

“The gut microbiome is thought to communicate with the brain in a complex, two-directional way,” said medical scientist Xiaoning Wang from the State Clinic Center for Geriatrics in China.

“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.”

More than a billion people worldwide are now thought to be obese, which leads to an increased risk for a multitude of different health issues, from cancer to heart disease. Knowing more about how our brains and guts are dependent on each other could make a huge difference in effectively preventing and reducing obesity.

“The next question to be answered is the precise mechanism by which the gut microbiome and the brain communicate in obese people, including during weight loss,” said biomedical scientist Liming Wang from the Chinese Academy of Sciences.

“What specific gut microbiome and brain regions are critical for successful weight loss and maintaining a healthy weight?”

The research was published in Frontiers in Cellular and Infection Microbiology.

An earlier version of this article was published in December 2023.