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Diet Soda or Sugar-Sweet?
Your Brain Knows the Difference When Your Taste Buds Don't
You may think that your diet soda tastes the same (maybe even better) than the sugar-sweetened variety, but your brain has a mind of its own when it comes to recognizing and discriminating calories.
In Brain Sense, I report on a group of California researchers who cranked up their MRI machines and talked twelve healthy women into having their brains scanned as they consumed varying concentrations of sucrose (real sugar) and sucralose (artificial sweetener). The scientists found that both sucrose and sucralose activated the same primary nerve pathways that send "sweet messages" to the brain from the tongue, but sucrose prompted a stronger response in several parts of the brain.
Furthermore, only sucrose stimulated production of the neurotransmitter dopamine. (Dopamine is known to be associated with feelings of pleasure and satisfaction.) The dopamine surged in midbrain areas that "lit up" when the women judged the sweet taste as pleasant. Those results, the researchers say, show that the brain distinguishes high-calorie sweeteners from calorie-free substitutes, even if the mouth does not.
In another study, Duke researchers genetically engineered mice to lack a particular ion channel in taste receptor cells. Without the receptor, the animals couldn't taste sweet foods.
The mice showed no interest in artificially sweetened (no-cal) water, but they demonstrated a marked preference for sugar (high-calorie sucrose) solutions, even though they had no ability to taste sweet things. Their preference was based solely on calorie content.
Recorded signals from the animals' brains showed that the high-calorie sugar produced a surge of dopamine release in the reward-seeking centers of the brain. And the more the better: the higher the caloric content, the greater the dopamine surge.
Fattening foods, the investigators concluded, have an express train ticket to the brain's motivational circuitry, even when their flavors can't be perceived.
For More Information:
Brain Sense, Part III: Taste
G. K. W. Frank, T. A. Oberndorfer, A. N. Simmons, M. P. Paulus, J. L. Fudge, T. T. Yang, and W. H. Kaye, "Sucrose Activates Human Taste Pathways Differently from Artificial Sweetener," NeuroImage (February 15, 2008) 39(4):1559-69.
I. E. de Araujo, A. J. Oliveira-Maia, T. D. Sotnikova, R. R. Gainetdinov, M. G. Caron, M. A. L. Nicholelis, and S. A. Simon, "Food Reward in the Absence of Taste Receptor Signaling," Neuron (March 27, 2008) 57:930-41.
