Rodent of the week: Fat rats, fructose and you*
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All those sugary sodas, those *fructose-laden (high-fructose corn syrup, as stated in an earlier version of this article, was not used in the study) candy bars and cereals might be delivering a double whammy in setting people up for obesity, assuming that people are a little like rats.
In rats, researchers from the University of Florida have reported in the American Journal of Physiology, a high-fructose diet blocks the appetite-controlling hormone leptin.
So it’s not just the fructose, a sugar found in moderate amounts naturally in fruits and vegetables, and in large amounts in the form of high-fructose corn syrup in many processed foods, that packs the pounds on. *(Though the Corn Refiners Assn. would like you to know that there are differences between fructose and high-fructose corn syrup in that, like table sugar, the syrup contains roughly equal amounts of fructose and corn syrup. For the industry’s arguments, see its fact sheet or press release.) The Department of Agriculture found that the consumption by Americans of high-fructose corn syrup increased by 1,000% from 1970 to 2000. It may be that a high-fructose diet makes the eater resistant to leptin, interfering with the body’s internal attempt to balance food intake and energy expenditure. The ‘I’m not hungry’ signal fails to go off, and rats, at least, forget how to push their little chairs away from the table.
Scientists have long linked leptin resistance to obesity, but the new study is the first to link fructose and leptin resistance.
The researchers studied two groups of rats, each group receiving the same amount of calories, according to a news release. But one group ate rat chow that contained 60% fructose, while the other was on a fructose-free diet. During that phase of the study, all remained equal. Both groups had identical body weight and fat as well as blood levels of leptin, insulin, glucose and cholesterol. The only difference was that high-fructose eaters had higher levels of blood triglycerides.
Then the researchers tested how each group of rats responded to leptin, and they discovered that those eating the high-fructose diet had become resistant to the hormone. When both groups were switched to a high-fat diet, those who had earlier eaten the high-fructose diet got fat, while the fructose-free group didn’t.
‘Fructose sets you up,’ says Philip J. Scarpase, professor of pharmacology and therapeutics at the UF College of Medicine and lead author of the study. ‘If these findings are applicable to humans, then there could be consequences of eating a diet high in fructose, but only if you also consume an excessive amount of calories. If you go on a trip, attend a celebration, or otherwise eat more than you usually eat, a person consuming a low-fructose diet may be able to handle it. But the individual who has set themselves up so that leptin no longer works will be unable to burn the extra calories, and now they gain a lot of weight.’
The findings, so far, apply only to rats. But suddenly, that weight gain after those out-of-town celebrations are starting to make a lot more sense to me.
-- Susan Brink