Fructose Effects on Brain Influence Overeating

A new study suggests that consuming fructose appears to cause changes in regional cerebral blood flow (CBF) that can lead to overeating.

Researchers at Yale University (New Haven, CT, USA) used arterial spin labeling magnetic resonance imaging (MRI) to quantify regional CBF in 20 healthy normal-weight adult volunteers, both before and after drinking a 75-gram beverage of pure glucose or fructose. The main outcome measures were relative changes in hypothalamic regional CBF after ingestion. Secondary outcomes included whole-brain analyses to explore regional CBF changes, functional connectivity analysis to investigate correlations between the hypothalamus and other brain region responses, and hormone responses to fructose and glucose ingestion.

The results showed that glucose ingestion increased functional connectivity between the hypothalamus and the thalamus and striatum, while fructose increased connectivity between the hypothalamus and thalamus, but not the striatum. Regional CBF within the hypothalamus, thalamus, insula, anterior cingulate, and striatum--the appetite and reward regions-- was reduced after glucose ingestion; in contrast, fructose reduced regional CBF in the thalamus, hippocampus, posterior cingulate cortex, fusiform, and visual cortex. Fructose ingestion was also associated with reduced systemic levels of the satiety-signaling hormone insulin. The study was published in the January 2, 2012, issue of the Journal of the American Medical Association (JAMA).

“Fructose ingestion produces smaller increases in circulating satiety hormones compared with glucose ingestion, and central administration of fructose provokes feeding in rodents, whereas centrally administered glucose promotes satiety,” concluded lead author Kathleen Page, MD, and colleagues. “Thus, fructose possibly increases food-seeking behavior and increases food intake.”

Fructose (fruit sugar) is a simple monosaccharide found in many plants and together with glucose forms sucrose, the sugar we eat. It is one of the three dietary monosaccharides, along with glucose and galactose, which are absorbed directly into the bloodstream during digestion. Because fructose is metabolized in the liver to glucose, it has the lowest glycemic index (19) of all the natural sugars. Excess fructose consumption has been hypothesized to be a cause of insulin resistance, obesity, elevated LDL cholesterol, and triglycerides, leading to metabolic syndrome.

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