Remember your first sip of coffee? Maybe you loved it, but there's a good chance you wondered how anyone could enjoy something so bitter. Yet for many people, coffee eventually becomes a favorite part of the day. So why do our tastes change?
It turns out that enjoying food may involve more than what happens on our tongues. A new study from the University of California, San Francisco, suggests the brain also learns from what happens after we eat, helping shape which flavors we come to prefer.
The research, published in Nature, identified a brain pathway that helps mice associate flavors with the nutrients they provide. Smaller human brain imaging studies revealed similar activity, although researchers haven't established whether the same process directly shapes food preferences in people.
Scientists have long known that dopamine, a chemical involved in motivation and learning, plays a role in how we respond to food. But while much of that research has focused on our immediate reactions to eating, the new study looked at signals that appear later, after nutrients reach the digestive system.
In experiments with mice, researchers found that nutrients triggered a slower, longer-lasting dopamine response. That response appeared to help the animals learn which flavors were associated with calories.
When scientists blocked the response, the mice still ate normally but no longer learned to prefer flavors linked to calories. When researchers artificially triggered it, the mice developed a preference for a flavor that contained no calories.
"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," said Zachary Knight, a UCSF professor of physiology and senior author of the study.
The researchers also examined brain scans from two smaller human studies involving 13 men and 38 adults. Both showed activity in a similar brain region after participants consumed nutrients, suggesting that people may have a related response.
That doesn't mean scientists have figured out exactly why we learn to love coffee, dark chocolate or other acquired tastes. The study didn't test those preferences directly, and our food choices are influenced by many things, including familiarity, culture and personal experience.
Still, the findings offer another piece of the puzzle. They suggest that what makes a food appealing may depend partly on what our brains learn after we've eaten it, not just how it tastes in the moment.
Researchers hope that understanding this process could eventually shed light on why certain foods become favorites and whether those preferences can change.
The research received support from the U.S. National Institutes of Health, Howard Hughes Medical Institute, German Research Foundation and German Centre for Diabetes Research.