New Delhi: Scientists have identified a previously poorly understood pathway linking the gut and brain that may help explain why people gradually develop a liking for foods and drinks they initially find unpleasant, such as bitter coffee.
Published in Nature on 4 November, the study, titled ‘The neural basis of flavour–nutrient learning’, was undertaken by researchers at the University of California, San Francisco (UCSF).
It found that nutrients reaching the digestive system trigger a slow dopamine response in a region of the brain involved in learning and emotional processing.
Dopamine is a chemical messenger involved in motivation, reward and learning. While its rapid response to pleasurable experiences is well understood, the researchers investigated how slower dopamine signals influence food preferences over time.
“We’ve shown that this slow dopamine system is what drives us to learn to like certain foods over time, and we can see where and how that happens,” senior author Zachary Knight told ScienceDaily.
Knight explained that once the brain associates coffee’s bitter taste with caffeine’s stimulating effects, “that coffee starts to taste a lot better”.
How the gut influences food preferences
To investigate the pathway, researchers introduced sugar water and a milkshake-like liquid directly into the stomachs of mice while monitoring dopamine activity in their brains.
They observed a prolonged dopamine response in the anterior basolateral amygdala (aBLA), a region involved in processing emotions and learning associations.
“We could see that this dopamine is part of a different system and begin to understand its role,” Knight said.
The researchers then tested whether the pathway was necessary for learning food preferences. When they disrupted it in mice, the animals continued eating normally but could no longer learn to associate unfamiliar flavours with receiving calories.
In another experiment, the team artificially stimulated the pathway after mice consumed a calorie-free flavoured liquid. The animals subsequently developed a preference for that flavour, despite receiving no nutritional benefit from it.
Together, the experiments suggest that the pathway helps the brain learn to associate flavours with the nutritional value of food.
Also read: The food we eat can decide what the brain remembers, says new US study
Stronger response in the brain’s left hemisphere
The researchers also examined data from previous human brain-imaging studies to explore whether a similar response occurs in people.
One study involving 13 men found that consuming a milkshake triggered dopamine release in the left aBLA. Another study, involving 38 adults, recorded increased activity in the same region after participants consumed glucose.
In both sets of findings, the response was stronger in the left hemisphere than in the right. The researchers said they were surprised by this difference, but why it occurs remains unclear.
The human imaging results provide supporting evidence for the pathway, although they do not establish that it plays the same causal role in people as it did in the mouse experiments.
Could the findings help change eating habits?
The researchers said a better understanding of the pathway could eventually help scientists develop treatments that influence food preferences.
They also raised the possibility that GLP-1 medications, which are used to treat diabetes and obesity, could affect the pathway. However, the study did not test these drugs, and their effects on this specific gut-brain connection remain unknown.
“By understanding the steps between nutrient detection in the gut and learning in the brain, it might be possible to fine-tune them to subtly change our preferences for different foods,” Knight said.
(Edited by Maryam Hassan)