Study: Brain Produces Fructose from Glucose
According to a new study by Yale School of Medicine researchers, fructose is converted in the human brain from glucose. The finding, published in thejournal JCI Insight, raises questions about fructose’s effects on the brain and eating behavior.
Fructose, a simple sugar, is generated in the human brain, according to Hwang et al. Image credit: Pete Linforth / Sci-News.com.
Fructose, or fruit sugar, is a natural simple sugar found in fruits, honey, vegetables, and many processed foods.
Excess consumption of fructose contributes to high blood sugar and chronic diseases like obesity.
Dr. Janice Hwang, an endocrinologist and an assistant professor in the Division of Endocrinology at the Yale School of Medicine, and co-authors had demonstrated in a prior study that fructose and another simple sugar, glucose, had different effects on brain activity.
But it was not known whether fructose was produced in the brain or crossed over from the bloodstream.
To investigate, the team gave eight healthy, lean individuals infusions of glucose over a four-hour period.
They measured sugar concentrations in the brains of the study participants using magnetic resonance spectroscopy (MRS). Sugar concentrations in the blood were also assessed.
“In this study, we use MRS scanning, which allows for noninvasive direct measurements of metabolite concentrations to test an alternate mechanism, namely that fructose is produced endogenously within the human brain from glucose via a metabolic pathway called the polyol pathway (glucose > sorbitol > fructose),” Dr. Hwang and her colleagues explained.
“The polyol pathway is an accessory glucose pathway that bypasses glycolysis, and in the setting of hyperglycemia, up to 30% of glucose can be metabolized via this alternate pathway.”
“Eight healthy subjects (4 women/4 men; age – 28.8 years) underwent MRS scanning to measure intracerebral glucose and fructose levels during a 4-hour hyperglycemic clamp.”
The researchers found cerebral fructose levels rose significantly in response to a glucose infusion, with minimal changes in fructose levels in the blood.
They surmised that the high concentration of fructose in the brain was due to the polyol pathway.
“In this study, we show for the first time that fructose can be produced in the human brain,” Dr. Hwang said.
“While the production of fructose in the brain had been seen in animals, it had not been demonstrated in humans.”
The finding raises several key research questions, which the authors plan to pursue.
“By showing that fructose in the brain is not simply due to dietary consumption of fructose, we’ve shown fructose can be generated from any sugar you eat. It adds another dimension into understanding fructose’s effects on the brain,” Dr. Hwang said.
“Glucose in the brain sends signals of fullness, but that is not the case with fructose.”
According to the researchers, the conversion of glucose to fructose in the brain also occurs in other parts of the body.
“This pathway may be one other mechanism by which high blood sugar can exert its adverse effects,” Dr. Hwang said.
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Janice J. Hwang et al. 2017. The human brain produces fructose from glucose. JCI Insight 2 (4): e90508; doi: 10.1172/jci.insight.90508
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