Fructose, a sugar widely consumed in the form of high-fructose corn syrup, may promote obesity and diabetes by overstimulating a hormone that helps to regulate fat accumulation, researchers reported on Monday.
The study, carried out at Harvard Medical School, marks the first time that scientists have identified a hormone that rises sharply and consistently in response to eating fructose. The finding suggests that people may vary in their sensitivity to the sugar, and that eventually it may be possible to test an individual for susceptibility to illnesses linked to weight gain.
Fructose stimulated the sharpest rise in the hormone in people who were obese, an increase that the researchers believe may trigger resistance to its effects, according to the study, which was published in the journal Molecular Metabolism. But even among lean people, there was wide variation in this response.
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When these sweeteners are consumed, glucose is absorbed into the bloodstream and ushered into tissues like fat and muscle with assistance from insulin. But fructose takes a different route.
The vast majority of it goes to the liver, where it stimulates the production of triglycerides, some of which are packaged into lipoproteins with cholesterol and secreted into the bloodstream.
A buildup of these triglycerides in the liver itself leads to nonalcoholic fatty liver disease, an increasingly common metabolic disorder that affects about 10 percent of children and as many as a third of all adults. Fatty liver often coincides with insulin resistance, a precursor to Type 2 diabetes, and it is a strong risk factor for heart disease.
“There’s no question that fructose is a sugar that promotes fat storage in the liver,” said Christopher B. Newgard, the director of the Sarah W. Stedman Nutrition and Metabolism Center at Duke University School of Medicine, who was not involved in the study. “In that sense, it’s a sugar that is a bad actor in the development of metabolic syndrome and Type 2 diabetes.”
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Glucose had only a minimal impact on the hormone, called fibroblast growth factor 21, or FGF21. But fructose increased its levels; the largest dose increased hormone levels fourfold within two hours on average.
The obese subjects had higher levels of FGF21 to begin with. And after they ate fructose, their peak levels of the hormone rose much higher than in the lean subjects.
FGF21 appears to be largely produced in the liver, and some researchers suspect that it helps to burn fat stores there and elsewhere in the body. But as fat accumulates and more of the hormone is released, the body may become desensitized to its effects.
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