Dieters beware---your brain can sense the amount of calories you consume and may be craving more.
A recent study released by Duke University Medical Center and published in the March 27 issue of Neuron magazine revealed that the brain showed a preference for higher-calorie foods regardless of taste, based on experiments conducted with mice.
"It is commonly observed that the pleasant taste of caloric foods is the main driver of feeling," said Ivan de Araujo, an assistant fellow at the John B. Pierce Laboratory affiliated with Yale University. "We [asked] whether in the absence of taste, we can have the physiological ability for an animal to develop a preference for something based on calories alone."
De Araujo, who co-authored the study during his time at DUMC, said the experiment was conducted using both normal mice and genetically engineered mice that lacked the gene that codes for taste reception-, known as "sweet-blind" mice.
The researchers then gave water sweetened with sucrose and normal water to the sweet-blind mice and observed how they chose what to drink.
"More than 80 percent of the time, [the sweet-blind mice] drank from the bottle associated with the sucrose," de Araujo said.
He noted that when a control experiment was performed with a non-caloric artificial sweetener substituted for sugar, the sweet-blind mice did not display a preference for the artificially sweetened water over the regular water. After several more control tests, the scientists concluded that the mice preferred the sucrose water for its caloric content.
These results mean that when people try to cut down on calories by eating less or drinking diet soda, the tactic might not work because the body's need for calories will make the person liable to eat more than they normally would, de Araujo said.
"One conclusion that can be drawn from this study [is that] substituting caloric foods with versions that are much less caloric but otherwise taste equally good might not be sufficient enough to sustain consumption in the long run," he added.
De Araujo noted that a recent study conducted by Susie Swithers, Grad '91 and an associate professor of psychological sciences at Purdue University, resulted in parallel findings that support his idea. The study at Purdue reported that when rats were fed artificially sweetened yogurt with regular food, they gained more weight.
Swithers said this can be attributed to the body's response of burning fewer calories when consuming caloric sweet things based on experiences eating sweets without calories.
She added that body temperature normally goes up when calories are consumed, but the rats who were fed artificially sweetened yogurt had a smaller body temperature increase when they were fed, which meant they were burning fewer calories.
Duke scientists continued their study by using probes to measure chemical levels in the brains of the normal and sweet-blind mice as they consumed the sugar water and artificially sweetened water.
De Araujo said that although dopamine levels in the normal mice's brains increased with the consumption of both sugar water and artificially sweetened water, the dopamine levels in the sweet-blind mice's brains rose only when they consumed the sugar water, meaning there is a taste-independent pathway to the brain's dopamine system.
Dr. Miguel Nicolelis, a senior author of the study and co-director of Duke's Center for Neuroengineering, said he hopes to spend more time studying the pathways the body uses to notify the brain of the caloric content of a meal.
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