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Glucose lights up the adolescent brain



SAN FRANCISCO – The developing adolescent brain may be responding differently to sugary drinks, leading to higher consumption of sugars and feeding the childhood obesity epidemic, according to researchers.

The findings come from a small, preliminary study that compared cerebral blood flow in 14 lean adolescents and 20 lean adults brains after the study subjects ingested 75 g of glucose.

Functional MRI scans revealed that glucose ingestion increased cerebral blood flow in the reward and executive function areas of the teens’ brains.

"This study is the first step in understanding what is occurring in the developing adolescent brain in response to drinking sugar," said Dr. Ania M. Jastreboff of Yale University, New Haven, Conn.

Several areas of the brain regulate food intake. They include the hypothalamus; the striatal region, which includes the putamen and caudate and is in charge of motivation and reward; the limbic region, where emotion and memory reside; and the cortical region, which includes the prefrontal cortex, insula, and the anterior cingulate cortex and handles the integration and processing of the brain.

In a previous study, Dr. Jastreboff and colleagues showed that "obese, but not lean, individuals exhibited increased activation in striatal, insular, and hypothalamic regions during exposure to favorite-food" (Diabetes Care 2013;36:394-402).

The group also has shown that glucose ingestion in lean adults reduced cerebral blood flow in appetite-regulation and reward-processing regions of the brain, Dr. Jastreboff said at the annual scientific sessions of the American Diabetes Association.

Subsequently, they wanted to find out if lean adolescent brains, compared with brains of lean adults, responded differently to glucose.

Among the subjects, the average body mass index was 22 kg/m2, and the mean age was 16 years for adolescents and 31 years for adults.

They came in at 8 a.m. after overnight fasting. They had a baseline MRI, drank 75 g of glucose, and had a functional MRI scan. Their labs were drawn every 10 minutes throughout the 1-hour scanning procedures.

Results showed that in lean adolescents, glucose ingestion increased cerebral blood flow in the striatum, insula, anterior cingulate cortex and the prefrontal cortex, all of which are regions of the brain that reside in the corticostriatal-limbic circuitry undergoing significant developmental changes during adolescence, said Dr. Jastreboff. There were no changes in hypothalamus and thalamus blood flow.

In contrast, consumption of the sugary drink in lean adults decreased cerebral blood flow in the hypothalamus, thalamus, striatum, insula, and the anterior cingulate cortex. There was no change in the prefrontal cortex.

"We hypothesize that these striking differences in brain response to glucose ingestion might contribute to adolescents’ higher consumption of added sugars," said Dr. Jastreboff.

She said that her group also conducted the study in obese adolescents and the results should be published soon. "What I can say is that the responses were different," she said.

The findings are far from definitive.

"I’m always skeptical that any test, if repeated the next day, will show the same thing," said Dr. Silva Arslanian, professor of pediatrics at the University of Pittsburgh. "The question is, is it an innate difference, or is it an environmental-driven difference?"

"But it’s definitely new data that needs to be pursued further to see what its translation is," said Dr. Arslanian, who was not involved in the study.

Dr. Jastreboff and Dr. Arslanian had no relevant disclosures.

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