Scientists have discovered a hidden gut-brain network that turns off cravings for sugar when the body needs more protein. T he body has a remarkable ability to recognise when it is missing important nutrients and adjust behaviour accordingly.
New research shows that the gut plays a much larger role in this process than previously understood, actively detecting protein shortages and communicating with the brain to influence food choices.
A team of researchers led by prominent neuroscientist and researcher at the Centre for Microbiome-Body-Brain Physiology at the Institute for Basic Science (IBS), SUH Seong-Bae, has now identified a previously unknown gut-brain communication system that helps animals seek out essential nutrients when protein is scarce.
Dr. Suh and his team from Seoul National University and Ewha Womans University, found that the gut does far more than digest food, as it continuously monitors nutritional status and can rapidly alter feeding behavior through a combination of nerve signals and hormones.
According to the findings published in the journal, Science on May 21, protein is a vital nutrient because it contains essential amino acids, which animals cannot produce on their own and must obtain through food. Scientists have long known that animals tend to crave proteinrich foods when such nutrient is lacking in their body.
However, the biological mechanism behind this behaviour has remained unclear. The researchers discovered that the gut responds to protein deficiency using two monitors nutritional state and directly guides behavioral interconnected signaling pathways.
One is a fast neural pathway that quickly alerts the brain when essential amino acids are in short supply while the other is a slower hormonal pathway that helps maintain protein-seeking behavior over a longer period.
To investigate how this system works, the team turned to fruit flies, which are widely used to study the neural circuits involved in feeding behaviour. Combining neural imaging, behavioural testing, and genetic techniques, the researchers mapped the circuitry responsible for detecting and responding to protein shortages. decisions,” said Dr. Seong-Bae Suh.
On how protein shortages change food preferences, the researchers found that the response was highly targeted rather than a simple increase in hunger. Instead of causing animals When flies were deprived of dietary protein, specialised cells in the intestine released a peptide hormone called CNMa.
This molecule served two functions. First, it activated enteric neurons associated with the gut, rapidly transmitting information about amino acid deficiency directly to the brain through a gutbrain neural circuit. Second, CNMa entered the bloodstream and reached the brain more slowly, where it reinforced and prolonged the drive to seek essential amino acids.
“Our study shows that the gut is not simply a digestive organ, but an active sensory system that continuously to eat more of everything, the gut-brain system altered dietary priorities. Protein-related nutrients became more appealing, while interest in sugar declined.
Further investigation showed that CNMa signaling suppressed the activity of sugar-sensing brain cells known as DH44 neurons. By reducing responses to carbohydrates, the system effectively shifted feeding preferences toward foods that could provide the essential amino acids the body lacked.
The study also highlighted a role for the gut microbiome, the gut bacteria that also influence cravings. According to the findings, fruit f lies that lacked their normal gut bacteria displayed stronger activation of brain neurons involved in amino acid seeking.
This finding suggests that gut microbes can influence feeding behavior by affecting nutrient availability and the signaling pathways that monitor nutritional status.
