You know you shouldn't have, but you've done it again. Whether it was a chocolate bar, bag of crisps or portion of chips, you simply couldn't resist.
"The devil made me do it!" you might plead in your defence. But as a new study shows, in truth it may have been your brain that made you do it.
To investigate the brain's role in the craving for high-fat, high-sugar foods, an international team of researchers led by the Cologne, Germany-based Max Planck Institute for Metabolism Research gave normal-weight persons a rich pudding twice daily for eight weeks in addition to their normal diet, and examined their brain activity both before and during the study.
A control group was given pudding with the same amount of calories but less fat and sugar.
"Our tendency to eat high-fat and high-sugar foods, the so-called Western diet, could be innate or develop as a result of being overweight. But we think that the brain learns this preference," says Sharmili Edwin Thanarajah, postdoctoral research fellow at the institute and lead author of the study, laying out the researchers' central hypothesis.
They found that brain activity greatly increased in the group that ate the high-fat, high-sugar pudding, which particularly activated the dopaminergic (i.e. involving dopamine) system, the region in the brain responsible for motivation and reward.
Dopamine is known as the “feel-good” hormone and important from an evolutionary standpoint. The brain releases large amounts of it when we do things required to survive and reproduce, such as eat and have sex.
"Our measurements of brain activity showed that the brain rewires itself when we consume chips and the like. It subconsciously learns to prefer rewarding food," explains study leader Marc Tittgemeyer, a professor and head of the translational neurocircuitry group at the German institute.
The combination of fat and sugar is especially "rewarding." As the researchers note in their study, "many modern processed foods are high in energy density and frequently contain both fat and sugar, which interact to potentiate reinforcement beyond the energetic value."
During the study, the test persons didn't gain more weight than those in the control group, and their blood levels, such as blood sugar and cholesterol, didn't change either. However, the researchers assume that their preference for fatty and sugary foods will continue beyond the end of the study.
"New connections are made in the brain, and they don't break up very fast," says Tittgemeyer. "After all, the whole point of learning is that once you learn something, you don't forget it so quickly."
The researchers' findings were published in the U.S.-based scientific journal Cell Metabolism. They caution that the study supports, but doesn't prove, their hypothesis, in part because of the small number of test persons (57). And the results, they add, could be different with people who are overweight, with a different snack or study duration.