by Marion Nestle
Mar 24 2010

HFCS makes rats fat?

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. Here’s the original paper.

It has long been known that feeding sugars to rats makes them eat more and gain weight.  But, as summarized in Table 1 in the paper, the researchers did only two experiments that actually compared the effects of HFCS to sucrose on weight gain, and these gave inconsistent results.  Their other experiments compared HFCS to chow alone.

The study is extremely complicated and confusingly described.  As best as I can tell, here’s what they found:

1.  The first study used 10 male rats in each group and observed them for 8 weeks.  At the end of the study, the rats fed chow alone weighed 462 grams.  The rats fed sucrose plus chow weighed 477±9 grams.   The rats fed HFCS plus chow weighed 502±11 grams.   The authors say the difference between 477 and 502 grams is statistically significant.  But these rats were offered the sugars for 12 hours per day.  The rats fed HFCS for 24 hours per day, which should be expected to be fatter, were not.  They weighed less (470 grams) than the rats fed sucrose for 12 hours per day.  So these results are inconsistent.

2.  The second study did not compare rats eating HFCS to rats eating sucrose.  It just looked at the effects of HFCS in groups of 8 male rats.

3.  The third study used female rats (number not given) and observed them for 7 months.  At the end of the study period, female rats fed HFCS plus chow for 12 hours a day weighed 323±9 grams.  Female rats fed sucrose plus chow under the same conditions weighed 333±10 grams.   This result is not statistically significant.

Although the authors say calorie intake was the same, they do not report calories consumed nor do they discuss how they determined  that calorie intake was the same.  This is an important oversight because measuring the caloric intake of lab rats is notoriously difficult to do (they are messy).

So, I’m skeptical.  I don’t think the study produces convincing evidence of a difference between the effects of HFCS and sucrose on the body weight of rats.  I’m afraid I have to agree with the Corn Refiners on this one.

So does HFCS make rats fat?  Sure if you feed them too many calories altogether.  Sucrose will do that too.

NOTE 3/26: see point-by-point response to this post by Bart Hoebel, one of the authors of the study, in the Comments below.

Addition, November 23: Thanks to Jeff Walker, professor of Biology at the University of Southern Maine, Portland, for doing a detailed critique of the study, most thoughtful and well worth a look.


[...] until Marion Nestle, the noted NYU nutritionist, critically assessed the Princeton study did the feeding frenzy abate. “I’m skeptical,” she decreed. [...]

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[...] whereas other people believe that it may. To be fair, the research that claims it causes obesity is disputed by renowned food researchers. That said, I’m not ready to jump on the HFCS is wonderful [...]

[...] Washington Post – Why HFCS is not so good for the Environment Marion Nestle – Why the CRA shouldn’t be allowed to rename HFCS to Corn Sugar Marion Nestle – Critique of newest study on how HFCS makes rats fatter compared to white sugar [...]

  • Quora
  • August 26, 2011
  • 11:19 pm

In his talk Dr. Lustig says that an extremely high percentage of fructose you consume gets directly converted to fat (~30%). What factors cause this percentage to go up or down? How much can this number go up or down?…

No. The Princeton study is badly flawed. Even Marion Nestle, a huge critic of the corn industry and of the HFCS “epidemic”, that is the addition of HFCS to anything that is sold, says: I don’t think the study produces convincing evidence of a differe…

[...] Nestle (Yes, THAT Marion Nestle) says this isn’t the magic bullet, and in fact, the study in of itself may have flaws. Although the authors say calorie intake was [...]

  • Nursing Student
  • April 14, 2012
  • 2:31 pm

100% Corn Syrup is 100% glucose.

Sucrose or Table sugar is 50% glucose and 50% fructose
HFCS (High fructose corn syrup) is 55% fructose and 45% glucose

Fructose is fruit sugar and it causes the growth of more adipose tissue (fat) while glucose is directly used for energy or stored as glycogen (complex stored sugar)

Any sugar if consumed and not used eventually turns into fat. Fructose more readily turns into fat because it is in a less ready form to be used as energy.


100% corn syrup is better for someone wanting energy and less fat and then sucrose next and then High fructose corn syrup last.

100% Corn Syrup————- 0% Fructose 100% Glucose
100% Sucrose (table sugar)–50% Fructose 50% Glucose
100% HFCS (High Fructose CS)55% Fructose 45% Glucose

I like corn, the pure stuff is better for you. Pancakes with syrup is one of the best things in the world.

A Nursing Student of Tri-County Technical College

[...] fact, even the biggest food scolds out there, the Center for Science in the Public Interest and Marion Nestle, have gone out of their way to note that—nutritionally speaking—the really isn't much [...]

[...] study found that HFCS, as it is known, causes more weight gain than sucrose in the same amount. But criticism of the study design left the finding in [...]

[...] found that HFCS, as it is known, causes more weight gainthan sucrose in the same amount. But criticism of the study design left the finding in doubt. And to date, no one has conducted a meta-analysis of all the high [...]

[...] makes a pretty good case for a connection between HFCS and an increase in body fat. OTOH, not everyone agrees. One of the authors defends the paper at Grist. Paul Ernsberger seems to be a pretty smart [...]

[...] we had evidence that HFCS caused more weight gain than other sweeteners. But then Marion Nestle trashed the study design. Another weird study emerged: the “Australian paradox” claimed [...]

[...] BoekeMarion Nestle, along with other nutritionists have joined the Corn Refiners Association in criticizing the recent Princeton study on High Fructose Corn Syrup. Indeed the very title of Nestle’s [...]

[...] recent debate is over a Princeton Study that concluded that it makes rats fat. There are plenty of articles critiquing the design of the study though) I think that it cannot be contested that Americans have [...]

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