An intriguing new study suggests that what really draws people to such treats, and prompts them to eat much more than perhaps they know they should, is not the fat that they contain, but primarily the sugar.
The new research tracked brain activity in more than 100 high school students as they drank chocolate-flavoured milkshakes that were identical in calories but either high in sugar and low in fat, or vice versa. While both kinds of shakes lit up pleasure centres in the brain, those that were high in sugar did so far more effectively, firing up a food-reward network that plays a role in compulsive eating.
To their surprise, the researchers found that sugar was so powerful a stimulus that it overshadowed fat, even when the two were combined in large amounts. High sugar shakes that were low in fat ramped up the reward circuitry just as strongly as the more decadent shakes that paired sugar and fat in large quantities, suggesting that fat was a runner-up to sugar, said Eric Stice, the lead author of the study, which was funded by the National Institutes of Health and published in The American Journal of Clinical Nutrition.
We do a lot of work on the prevention of obesity, and what is really clear, not only from this study but from the broader literature over all, is that the more sugar you eat, the more you want to consume it, said Dr Stice. As far as the ability to engage brain reward regions and drive compulsive intake, sugar seems to be doing a much better job than fat.
The new findings add to a growing number of brain studies that provide a more complex understanding of what drives people to overeat in the first place.
Heavily processed foods loaded with fat and sugar activate and potentially alter the same reward regions in the brain that are hijacked by alcohol and drugs of abuse. Though the extent to which these foods can provoke addictive behaviour remains controversial, the results may help explain why millions of people who diet and struggle to lose weight ultimately fail.
The obesity epidemic and the problems with overeating dont have too much to do with people overeating fruits and healthy foods. They have a lot to do with people overeating excess sugars and fats, said Nicole Avena, a faculty member at the New York Obesity Research Center at Columbia University, who was not involved in the new study.
Dr Avena said people can have all the willpower in the world. But if the brain reward system is activated in a way that causes them to have a battle against their willpower, then it can be very difficult for them to control their intake.