Today, more than 1 billion people around the world live with obesity, a condition that increases the risk of cardiovascular disease, diabetes, and some types of cancer. However, losing weight and keeping it off can be very difficult. The body does not simply respond to a decrease in calories. Signals from the gut, hormones, metabolism, and brain can all influence hunger, cravings, and weight regain.
One approach that is gaining increasing interest is intermittent energy restriction (IER). This is a form of diet that involves a period of reduced caloric intake followed by a more typical diet. A study published in 2023 suggests this strategy may do more than just help you lose weight. It is also possible that the relationship between intestinal bacteria and brain activity changes in a way that is closely related to appetite and eating behavior.
“Here we showed that the IER diet alters the brain-gut-microbiome axis in humans. The changes in the activity of the gut microbiome and addition-related brain regions observed during and after weight loss are highly dynamic and interlocked over time,” said previous author Dr. Qiang Zeng, a researcher at the Health Management Institute of the PLA General Hospital in Beijing.
intermittent fasting and the brain
To find out what happens inside the body during weight loss, researchers studied 25 obese adults in China. The average age of the volunteers was approximately 27 years, and their BMI ranged from 28 to 45.
The team used several tools to track changes over time. To determine the composition of the gut microbiome, stool samples were analyzed by metagenomics. Blood tests were used to monitor metabolic and physiological changes. The researchers also used functional magnetic resonance imaging (fMRI) to examine activity in brain regions involved in appetite, emotion, attention, learning, inhibition, and reward.
“A healthy and balanced gut microbiota is important for maintaining energy homeostasis and normal body weight. In contrast, an abnormal gut microbiota can affect specific brain regions involved in addiction and change our eating behavior,” explained co-author Yongli Li, Ph.D., from the Department of Health Management, Henan Provincial People’s Hospital, China.
Carefully managed weight loss program
The study began with a highly controlled fasting phase of 32 days. During this period, participants consumed a diet designed by a nutritionist. Their caloric intake was gradually reduced in a stepwise manner until they reached about a quarter of their basic energy needs.
This was followed by a 30-day low controlled fasting phase. During this phase, participants were given a list of recommended foods rather than a fully cooked meal. A person who follows this plan exactly will burn 500 calories per day for women and 600 calories per day for men.
By the end of the intervention, participants had lost an average of 7.6 kilograms, which was approximately 7.8% of their starting body weight. Body fat and waist circumference also decreased.
Metabolic improvements extended beyond weight. Blood pressure decreased, as did fasting plasma glucose, total cholesterol, HDL, LDL, and the activity of key liver enzymes. According to the researchers, these changes suggest that intermittent energy restriction may help reduce obesity-related problems such as high blood pressure, hyperlipidemia, and liver dysfunction.
Changes in the brain and gut occur in tandem
Researchers found that weight loss programs were associated with reduced activity in several brain regions involved in appetite and addiction-related behaviors. These changes may help explain why diet affects not only body size but also food cravings, self-control, and motivation to eat.
At the same time, the gut microbiome also changed. abundant Faecalibacterium prausnitzii, Parabacteroides distasonisand bacterocles uniform It skyrocketed. Escherichia coli decreased.
Further analysis suggested that specific microorganisms were associated with activity in specific brain regions. abundant Escherichia coli, Coprococcus is comingand Eubacterium hali was negatively correlated with activity in the left infraorbital frontal gyrus of the brain, an area involved in executive function and willpower during weight loss.
Other bacteria showed the opposite pattern. P. Distasonis and Flavonifractorpuruti They were positively associated with brain regions involved in attention, motor inhibition, emotion, and learning.
These findings point to the surprising possibility that as people lose weight, their gut microbiota and brain may change along with it. The study cannot prove whether gut bacteria cause changes in the brain, whether the brain causes changes in microbes, or whether another factor influences both. Still, the results confirm that weight management is more than just a matter of willpower and calories. This may involve a change in the biological conversation between the gut and the brain.
Two-way conversation inside the body
“The gut microbiome is thought to communicate with the brain in a complex, bidirectional way. The microbiome produces neurotransmitters and neurotoxins that access the brain via nerves and blood circulation. In turn, the brain controls eating behavior, while nutrients from our diet change the composition of the gut microbiome,” said co-author Xiaoning Wang, Ph.D., from the Institute of Gerontology, People’s Liberation Army General Hospital.
This two-way communication may help explain why obesity is so difficult to treat. Hunger, cravings, mood, reward, and metabolism are all shaped by biological signals. The gut microbiome can produce compounds that affect inflammation, metabolism, and nervous system activity. The brain helps control food choices and eating behavior.
The 2023 findings suggest that successful weight loss may involve changes in this entire system, rather than in one isolated organ.
What was added in later research
Research published since the 2023 study continues to support the idea that fasting can affect the gut microbiome, but the evidence remains mixed. A 2024 systematic review of human studies found that intermittent fasting appears to affect the abundance, diversity, and composition of gut microbes. However, the authors also noted that results vary widely from study to study, and more research is needed to determine which changes are truly beneficial to health.
Another clinical study in 2024 compared intermittent fasting combined with protein pacing to continuous calorie restriction in overweight or obese adults. Both diets reduced calorie intake, but the fasting and protein pacing groups had greater weight loss and more pronounced changes in the gut microbiome. Researchers reported increases in microbial and metabolic signals associated with improved body composition and fat loss.
Taken together, these recent findings strengthen the larger picture that fasting-based interventions have the potential to reshape the gut microbiome in a meaningful way. However, it also shows that details matter. Fasting type, caloric intake, protein intake, fiber intake, meal timing, and personal biology can all influence results.
The next question in weight loss research
The original study in 2023 was small and correlational, so it cannot show cause and effect. We also focused on specific participant groups and short-term interventions. Larger, longer-term studies will be needed to determine whether specific microbes or brain regions can reliably predict who loses weight, who keeps it off, and which diets are most effective for different people.
Co-author Dr. Liming Wang, also from the Institute of Health Management in Beijing, said: “The next question to answer is: What are the precise mechanisms by which the gut microbiome and brain communicate with obese people, including during weight loss? Which specific gut microbiome and brain regions are important for successful weight loss and maintenance of a healthy weight?”
For now, this study provides a more detailed view of what happens during intermittent fasting. Weight loss may not be limited to shrinking fat stores. Synchronous changes in gut bacteria, metabolism, and brain activity may also be involved in altering the body’s response to food.
