A Princeton University research team has demonstrated that all sweeteners are not equal when it comes to weight gain: Rats with access to high-fructose corn syrup gained significantly more weight than those with access to table sugar, even when their overall caloric intake was the same.
In addition to causing significant weight gain in lab animals, long-term consumption of high-fructose corn syrup also led to abnormal increases in body fat, especially in the abdomen, and a rise in circulating blood fats called triglycerides. The researchers say the work sheds light on the factors contributing to obesity trends in the United States.
I was rather excited about this--I sometimes teach simultaneous biochemistry and statistics courses for nursing students, and a paper like this would be ideal--combining carbohydrate chemistry, data analysis, and dieting. It would be bound to pique their interest.
Unfortunately for my purposes, the press release veered into diet-guru pseudoscience right away, speculating that
as a result of the manufacturing process for high-fructose corn syrup, the fructose molecules in the sweetener are free and unbound, ready for absorption and utilization. In contrast, every fructose molecule in sucrose that comes from cane sugar or beet sugar is bound to a corresponding glucose molecule and must go through an extra metabolic step before it can be utilized.
Really, that's their explanation? Hydrolysis is an extra metabolic step here? I suspected that the researchers were not responsible for the flaky press release, so the next step should be the actual article. The press release said the article was published online Feb. 26, but it provided no link. Still, search engines soon took me to the abstract: High-fructose corn syrup causes characteristics of obesity in rats: Increased body weight, body fat and triglyceride levels. The abstract seems reasonable enough--no speculation about metabolic pathways, no suggestions that fructose calories are qualitatively different than sucrose calories. Unfortunately, the abstract is all you get from the publisher, unless you wish to purchase the full text for $31.50 USD. My adjunct professor status doesn't cover such costs.
Meanwhile, everywhere I looked, there were blog posts and science news articles concluding that if we switch to soda pop sweetened with sucrose, it will keep us from getting fat. Much as I would like to eat more sugar and lose weight, I'm pretty sure that's not going to happen.
As I went about trying to sort out this puzzle without spending $31.50, I found some helpful and interesting discussions of the article (listed in the links below), and this afternoon a Slashdot commenter provided a pre-print of the actual paper.
The press release conflated the two experiments described in the article, overstated the differences in weight gain, left out the data from female rats (which seemed to contradict the male rat results) and didn't mention how small (eight rats per group) the treatment groups were in the long term study. If you look at the table of final weights for the short-term study, the rats that had sucrose to drink 12 hours a day had the same mean final weight as the 24-hour-a-day corn-syrup drinkers. The group with a statistically significant difference was the 12-hour-a-day corn syrup drinkers, and their standard error bars came very close to overlap. Given that there were only 10 rats per treatment, I'd hardly call this a definitive finding.
The graph on the right shows the inconclusive results in female rats in the 6-month study. Over all, I'd say this is an interesting little study over-hyped by Princeton's PR department. If it's now true in science, as in Hollywood, that there is no such thing as bad publicity, these researchers can look forward to some more funding.
Here are some of the links I found informative or interesting.
- High-fructose corn syrup causes characteristics of obesity in rats: Increased body weight, body fat and triglyceride levels. by Miriam E. Bocarsly, Elyse S. Powell, Nicole M. Avena, and Bartley G. Hoebel. Also available: pre-print of the actual paper.
- The press release: A sweet problem: Princeton researchers find that high-fructose corn syrup prompts considerably more weight gain
- The Industry Response: Gross Errors in Princeton Animal Study on Obesity and High Fructose Corn Syrup Research in Humans Discredits Princeton Study from the Corn Refiners Association. The "gross errors" they mention are in the press release, not the study, but hey, it's PR--who cares if it's true?
- High Fructose Corn Syrup Causes Bigger Weight Gain In Rats at Slashdot. The comments were very helpful. Here's where I found links to the full text of the article (without paying $31.50) and also the Ars Technica and LA Times critiques. There were some nice technical discussions of the enzymatic pathways involved in fructose vs. glucose metabolism, some pseudo-scientific rants, and some funny comments as well. Slashdot can be so great.
- Does high-fructose corn syrup make you fatter? Ars Technica is more harshly critical of the original article than I am. Really, it's a fine line between convincing editors to publish and overstating your results.
- A not-so-convincing case that high fructose corn syrup is worse for you than sugar. The LA Times also finds fault with the study.