By Aria Bendix -
NBC News
Food preferences are not always something we are born with.
A study published last Wednesday in the journal Cell Metabolism suggests that eating fatty or sugary snacks alters our brain activity and creates long-lasting preferences for these less healthy foods.
For the study, researchers from Yale University and the Max Planck Institute for Metabolism Research in Germany gave one group of participants a high-fat, high-sugar yogurt twice a day for eight weeks, while another received a version low in fat and sugar.
Other than that, both groups maintained their normal eating habits.
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In the end, the groups evaluated puddings with different concentrations of fat and apple juices with different levels of sugar.
The group that ate the high-fat, high-sugar yogurt said they didn't like the low-fat pudding and didn't want the low-sugar apple juice as much as they did at first.
Next, the participants underwent MRI scans while drinking shakes.
The scans showed that the treat increased brain activity in the group that had eaten the high-fat, high-sugar yogurt, but not in the other.
The researchers concluded that fatty and sugary snacks activate the brain's dopaminergic system, which gives people a sense of motivation or reward.
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“Let's say a new bakery opens next to your work and you start going in and eating a bun every morning.
That alone can rewire basic dopamine learning circuits," says Dana Small, lead author of the study and director of the Center for Research on Modern Diet and Physiology at Yale University School of Medicine.
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This is an intuitive idea for anyone who has gotten into the habit of eating dessert frequently - for example, during the holidays - and has found it difficult to break that pattern.
Small says that diet has such a strong effect on brain activity that dopamine signals can fire even when someone anticipates eating fatty or sugary foods, such as when they pass a bakery or smell a cake.
"This tells us how sensitive we are to the food environment and how it can change our behavior," he says.
Sugary and fatty foods alter brain activity
The new study was small: it included only 49 people, all of whom were healthy, did not smoke or take medication, and were not overweight or obese.
Overall, the participants did not gain a significant amount of weight over the eight weeks.
Small says this study is the first in humans to show that even small changes in diet can alter brain circuitry and increase the long-term risk of overeating or gaining weight.
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Previous research has shown that obesity can alter people's brain activity, with people having an innate dislike for bitter foods and a penchant for sweet ones.
Experiments with rodents, meanwhile, have shown that foods high in fat and sugar can rewire dopaminergic neurons and lead to overeating.
But scientists knew less about how human eating habits influence food preferences.e
"There is now enough evidence to be fairly certain that this occurs, and it occurs in multiple species," Small said.
Susan Swithers, a behavioral neuroscientist at Purdue University who was not involved in the research, said it's possible that people start to prefer foods they eat regularly and then gravitate toward them.
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“People think we eat what we like, but we actually like what we eat,” Swithers says.
According to Garrett Stuber, a professor of neuroscience at the University of Washington who was not involved in the study, there may even be biological reasons why people prefer fatty and sugary foods.
Early humans likely sought energy foods high in carbohydrates and fat, so people today might instinctively share those preferences.
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“Thousands of years ago, these foods were very rare and not as abundant, but the fact that they are now in almost everything we eat goes against biology,” says Stuber.
How much can food preferences change over time?
One question that remains to be answered, according to Small, is whether people can change their preferences after becoming accustomed to a diet high in fat and sugar.
“It may be the case that gradually decreasing to more acceptable levels of fat can change preferences in a more sustainable way over time.
But I don't think we know,” she said.
A 2012 study showed that after being routinely exposed to soups with no added salt, people ended up liking those soups just as much as the saltier versions.
Small said this process may work for fat and sugar as well.
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But Stuber says it's hard for people to forget that fatty and sugary foods taste good.
“If you stop presenting something to people, something that is rewarding, that memory doesn't go away,” he said.
When it comes to not liking certain foods, those preferences can last a lifetime.
"Think, for example, of food poisoning: You can eat a food and get sick from it, and you'll have a long-lasting aversion to that food," Stuber said.