People love to hate high fructose corn syrup. Though its chemical content is nearly identical to that of table sugar, it is frequently blamed for causing the obesity “epidemic” in the U.S. The finger-pointing has become so intense that food manufacturers now brag that their products are HFCS-free. (My favorite example is Log Cabin Lite syrup, which touts that it contains “natural sugar” while simultaneously trying to emphasize its “reduced calorie” status.)

So perhaps it’s no surprise that many consumers embraced a recent study from Princeton University finding that the corn-based sweetener caused rats to gain more weight than rats that ate sugar.

Princeton researchers allowed three groups of male rats to eat as much rat chow as they pleased. One group also had access to a 10% sugar solution for 12 hours each day; a second group was allowed to drink an 8% HFCS solution for 12 hours each day; and a third group could drink the HFCS solution without any restrictions. A fourth group of rats got chow only.

After eight weeks, three groups of rats weighed essentially the same – the chow-only rats (462 grams on average), the 24-hour HFCS rats (470 grams) and the sugar-water rats (477 grams). But the rats that were able to drink the HFCS solution for 12 hours each day weighed in at an average of 502 grams, a difference that was deemed statistically significant.

How could this be? It wasn’t simply the calories in high-fructose corn syrup. The fat rats drank 21.3 calories' worth of the sweetener each day, only slightly more than the 20.1 calories sipped by rats with 24-hour access to the HFCS solution. What’s more, the rats that were offered sugar water consumed 31.3 calories worth of sweetener each day.

The researchers don’t offer a clear answer, but they suggest that the extra fructose in high-fructose corn syrup may be to blame. Table sugar is made of equal parts fructose and glucose, while HFCS contains 55% fructose, 42% glucose and 3% other sugar molecules called higher saccharides.

As the researchers explain in their paper, fructose is known to interfere with the body’s natural system for telling the brain when to stop eating. Fructose is also easier for the body to metabolize. But it’s still not clear how – or even whether – these facts make HFCS more dangerous than sugar. Nor is it clear why the effect would only be seen in rats that consumed HFCS for 12 hours a day but not those who were able to drink it 24 hours a day when both groups wound up drinking approximately the same amount overall.

Complicating things further, the researchers cite a related study of female rats that found no difference in weight gain between animals that consumed HFCS or sugar over an eight-week period.

In another phase of the Princeton study, the researchers found that rats allowed to drink the HFCS solution gained more weight over six months than rats with no access to a sweetened beverage. The difference was dramatic: rats with 24-hour access to HFCS gained 27% more weight than the rats stuck with chow only. But the researchers didn’t include a third group of rats with access to sugar, so it’s impossible to say whether HFCS was worse than regular sugar.

(Why didn’t they test the long-term effects of sugar? The researchers said it wasn’t necessary because sugar consumption didn’t affect body weight in their first experiment. True, but neither did HFCS when made available for 24 hours a day, and they did test that.)

The researchers remedied this problem in a third experiment involving female rats. Over a seven-month period, rats that were able to drink sugar water for 12 hours a day gained 183% of their body weight – the exact same amountas rats who could drink HFCS solution for 12 hours a day.

However, female rats with 24-hour access to HFCS boosted their body weight by 200%.

It’s not clear why high-fructose corn syrup was more fattening over an eight-week period when it was available for 12 hours of the day (but not 24), yet the opposite was true when the experiment lasted for seven months. In an e-mail, the researchers explained that the difference could be due to the fact that male rats were used in one experiment and female rats were used in the other.

The study was published online last month in the journal Pharmacology, Biochemistry and Behavior, though Princeton publicists called attention to it just this week. The results have been much discussed in the blogosphere (including this response from the Corn Refiners Assn., the trade group representing makers of high fructose corn syrup).

The researchers concluded “over-consumption of HFCS could very well be a major factor in the ‘obesity epidemic,’ which correlates with the upsurge in the use of HFCS.” It might be. But to my mind, these experiments hardly prove it.

-- Karen Kaplan

Photo: Too much high fructose corn syrup is bad for you, but so is too much sugar. Photo credit: Hal Wells/Los Angeles Times