Tuesday, March 30, 2010;
Adapted from The Post's daily health blog.The tangled tale of the Princeton rats
Princeton University recently circulated an article announcing a study finding that rats that consumed lots of high-fructose corn syrup became obese. The authors conclude, "Translated to humans, these results suggest that excessive consumption of HFCS may contribute to the incidence of obesity."
As might have been expected, the HFCS industry quickly responded. But others with less direct interest in the outcome have voiced criticism, too, notably Marion Nestle, a professor in the Department of Nutrition, Food Studies and Public Health at New York University and author of the Food Politics blog. In her entry about the study, she writes:
"I can hardly believe that Princeton sent out a press release yesterday announcing the results of this rat study. The press release says: '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.' How they came to these conclusions is beyond me."
Among Nestle's chief complaints: Though the study claims that all the rats consumed the same number of calories, nowhere does it actually say how many calories. Plus, the whole thing seems poorly designed, with rats consuming different combinations of HFCS, sucrose and rat chow for varying periods, making straight comparisons difficult.
I contacted Bart Hoebel, the professor at Princeton who worked with the research team. Here are excerpts from the questions I e-mailed him, and his answers:
Jennifer LaRue Huget: Can you explain how reliably rat-study results translate to humans?
Bart Hoebel: The rat is much like the human in regard to feeding behavior and basic metabolism. Rats evolved eating a diet something like ours; in some cases our own garbage. Thus the rat is a reasonable "animal model" of human feeding behavior in many cases. . . . The results do not apply directly to humans, but strongly suggest the need for more experiments along these lines.
JLH: Marion Nestle criticized the study for not being clear about the rats' calorie consumption. Can you speak to that?
BH: She says: "Although the authors say calorie intake was the same, they do not report calories consumed."
We say: Caloric intake was reported in the Results section for Experiment 1.
She says: "Nor do they discuss how they determined that calorie intake was the same."
We say: In the Methods section we explain that we measured HFCS, sucrose and chow intake daily. We computed the calories consumed, which is also described.
She says: "This is an important oversight because measuring the caloric intake of lab rats is notoriously difficult to do (they are messy)."
We say: We do not see any oversight. The drinking tubes had an anti-drip device built in and we collected spillage for the food pellets for accuracy. We reported the caloric intake and the standard error, which shows the variability in intake for a given group.
JLH: Something about the way the study was written sounds as though researchers set out to link HFCS to obesity, not to determine whether such a link exists.
BH: The study was designed to explore the comparison of HFCS with sucrose and at the same time to compare 24-hour access with 12-hour access, plus males with females. Keep in mind that this is research, and one does not know which will be the key results when starting out. We discovered that male rats drinking HFCS were heavier than the matched sucrose controls in Experiment 1 and heavier than the other groups in Experiment 2. Regarding females, again the HFCS rats were the heaviest; although the sucrose control group had sugar available for less time per day, we had reason to think this was not a critical variable. . . . Moreover the females, like the males, showed elevated triglycerides and increased fat deposits. This is all explained in the article for anyone who wants to study it carefully.
-- Jennifer LaRue Huget