One important caveat must be mentioned; all experiments involved food and water deprivation. Thus, the observed activation of the dopamine reward system by calorie load in this paper may be affected by the food-restricted state of the mice.
This study raises many intriguing future questions. How is calorie load sensed by the dopamine reward system? Do certain sugars (for instance, fructose) affect the dopamine reward system in different ways? Does the same phenomenon occur when calories come from different food types? For example, do calories from fat have a stronger affect? All of these questions are important to understand the underlying causes of human obesity. Understanding the rewarding properties of certain foods will help us to design effective ways to restrict the desire to eat once the need to eat is fulfilled. This study also adds to the growing body of information showing that metabolic cues are not solely the domain of the hypothalamus and that much more crosstalk occurs between metabolic cues and higher brain centers involved with the desire to eat than previously believed. Thus, categorizing food intake as hedonic versus homeostatic may not only be redundant but misleading. When it comes to eating, need and desire aren’t so separate after all.
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