Researchers at U of G and Rockefeller University in New York City compared the effects of high-fructose corn syrup (HFCS), sucrose and saccharin in rats, and found similarities in animals fed HFCS and in rats consuming cocaine in earlier work.
HFCS typically contains 55 per cent fructose and 42 per cent glucose, while sucrose contains a 50:50 mix.
The researchers wondered whether slightly more fructose affected rats differently, said Prof. Francesco Leri, Department of Psychology.
“Can small differences in fructose/glucose ratios really alter behaviour, brain and physiology? We wanted to see how rats responded to various combinations of these sugars,” he said.
Over two years, they studied how much HFCS the animals self-administered and looked at behavioural and biological effects.
Rats fed different ratios of fructose and glucose showed differences in self-administration behaviour and in neural activity in brain regions involved in food reward and appetite.
The researchers then compared the effects of HFCS used in making human-grade food with the effects of sucrose and saccharin. The rats were fed using a new self-administration procedure pioneered by PhD student AnneMarie Levy.
Saccharin self-administration was relatively low, probably because of its zero-calorie content, said Levy.
Rats consuming HFCS regularly showed high sugar-seeking behaviour, unlike rats consuming sucrose.
“When we studied the brains of these rats, we noticed significant differences,” Levy said.
“More specifically, expression of dopamine and opioid receptor genes in HFCS rats was similar to what has been observed in animals that self-administered cocaine.”
In 2013, Leri’s laboratory found that preferences for Oreo cookies could predict cocaine self-administration.
In another study, the researchers gave rats unlimited access to HFCS or sucrose solutions for more than a month.
“We found that those rats exposed to HFCS consumed fewer calories overall but, surprisingly, their livers displayed a higher concentration of a polyunsaturated fatty acid that can lead to increased inflammation,” Leri said.
“Across all experiments, we observed that it took less exposure to sugars with a higher fructose ratio to lead to both neural and physiological responses associated with addictive and metabolic diseases.”
The study is published in a special edition on food addiction in the journal Nutrients.
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