Editors' ChoiceObesity

The bitter price of sweetness

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Science Translational Medicine  20 May 2015:
Vol. 7, Issue 288, pp. 288ec81
DOI: 10.1126/scitranslmed.aac4993

A festering global health problem, the obesity epidemic can be explained by the simple concept of energy balance—that is, the equilibrium between caloric intake and energy expenditure. More complicated, however, are the precise factors that contribute to the sustained positive energy balance enjoyed by most Americans and spreading to other countries around the world. In addition to the obvious lifestyle choices, which include sedentary behavior and consumption of calorically dense foods, more subtle behavioral, biological, genetic, and nutritional factors are important determinants of obesity. For example, there is mounting evidence for the obesogenic effects of fructose, a nutritional sweetener identical to glucose in calories but sweeter and distinct in its metabolism. A recent paper by Luo and colleagues provides new insights into how dietary fructose influences appetite behaviors and the brain’s response to food cues.

The study enrolled 24 healthy men and women who consumed 75 g of either fructose or glucose in a randomized, double-blind crossover study. After drink ingestion, the investigators presented pictures of tasty foods (pizza, cookies, candy) or non-food control images (baskets, buildings) to participants and used functional magnetic resonance imaging to examine activity in eight brain regions known to be responsive to food cues. The activity of several brain regions was higher after the fructose drink compared with glucose, as were appetite ratings. A fascinating element of the study was the food decision-making exercise in which participants were given a choice between immediate food rewards or delayed monetary compensation. Fructose intake appeared to shift the participants’ willingness to choose immediate food rewards over delayed monetary compensation.

These new findings provide a compelling link between fructose consumption and obesity through effects on appetite and food-related behaviors. Plasma insulin levels differed greatly between the glucose-fed and fructose-fed subjects and likely account for at least part of the observed effects of glucose and fructose on the central nervous system. The presence of insulin receptors in key brain regions involved in appetite responses and reward supports this concept and provides a link between appetite regulation and hormonal responses to distinct monosaccharides.

S. Luo et al., Differential effects of fructose versus glucose on brain and appetitive responses to food cues and decisions for food rewards. Proc. Natl. Acad. Sci. U.S.A. 10.1073/pnas.1503358112 (2015). [Full Text]

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