by Marion Nestle
Nov 27 2012

HFCS v. Diabetes: Correlation does not mean causation.

The latest study on the evils of High Fructose Corn Syrup (HFCS) so annoys the Corn Refiners Association that it broke the study’s embargo.

Reporters were not supposed to write about the study until today, but the Corn Refiners issued a press release yesterday: “Caution: New Study Alleging HFCS-Diabetes Link is Flawed and Misleading.”

The New York Times quickly posted its own pre-embargo account.

Why the fuss?  The study reports that countries with the highest levels of HFCS in their food supplies also have a 20% higher prevalence of diabetes in their populations.  This is a correlation between HFCS and diabetes.  It does not mean that HFCS causes diabetes—an important distinction.

But the authors’ press release (sent to me in an e-mail message) makes it sound like causation.  They say (also see Dr. Goran’s comments added to this post below):

HFCS appears to pose a serious public health problem on a global scale,” said principal study author Michael I. Goran…The study adds to a growing body of scientific literature that indicates HFCS consumption may result in negative health consequences distinct from and more deleterious than natural sugar.

This conclusion is based on their observations that the amounts of other sugars in the food supplies of countries with high and low HFCS are about the same.  But HFCS is a form of sugars that adds to total sugar availability.

The authors obtained information about diabetes and obesity prevalence and HFCS and other dietary factors in the food supply from existing sources of data, all of them questionable.   The data do not distinguish between type 1 and type 2 diabetes, for example, and the two different sources of data on diabetes prevalence give different results.

Inconsistencies abound.  For example, Mexico has more diabetes than does the U.S., but rather low HFCS availability (Mexicans prefer sucrose in their sodas).  Some countries with high diabetes rates report no HFCS availability at all.

As with all correlational studies, something else could be going on that causes HFCS, sugars of all types, and diabetes to increase.

That was the point I was trying to make when I spoke to Stephanie Strom of the New York Times:

 “I think it’s a stretch to say the study shows high-fructose corn syrup has anything special to do with diabetes,” Dr. Nestle said. “Diabetes is a function of development. The more cars, more TVs, more cellphones, more sugar, more meat, more fat, more calories, more obesity, the more diabetes you have.”

She noted that the study “falls right in the middle of the Corn Refiners fight with the Sugar Association,” a reference to the legal war being waged between the two industry groups over the marketing of high-fructose corn syrup.

The Corn Refiners press release quotes its president, Audrae Erickson:

This latest article by Dr. Goran is severely flawed, misleading and risks setting off unfounded alarm about a safe and proven food and beverage ingredient.  There is broad scientific consensus that table sugar and high fructose corn syrup are nutritionally and metabolically equivalent…The bottom line is this is a poorly conducted analysis, based on a well-known statistical fallacy, by a known detractor of HFCS whose previous attack on the ingredient was deeply flawed and roundly criticized.


Yes, HFCS is sugar(s)—glucose and fructose.  So is table sugar (sucrose).

But the bottom line goes for both: Everyone would be better off eating less sugar(s).

Addition to post: Dr. Goren wrote two e-mails to me in response.  With his permission, they follow.

Hi Marion,

I saw your comments in the NYT article that was published about our global HFCS paper.

You say that: “Diabetes is a function of development. The more cars, more TVs, more cellphones, more sugar, more meat, more fat, more calories, more obesity, the more diabetes you have.”

I wanted to mention that an often overlooked issue is that obesity is not the only factor contributing to type 2 diabetes and even the causal link between obesity and type 2 diabetes is unknown. Other factors include inflammation, oxidative stress, insulin resistance etc. In the study that was done with my colleague at the University of Oxford, the countries with high and low/zero HFCS were matched for obesity levels as well as total calorie and sugar availability. In essence this allowed us to isolate the effects of HFCS as a contributing factor, independent of obesity and the other factors that you mention that are related to obesity. I agree, as stated in the paper, that the ecological type analysis has its limitations, but in the case of HFCS it provided an opportunity to study its effects at the broader macro level. We did this because it is impossible to evaluate individual levels of HFCS consumption because we don’t know specifically how much is added to food/beverages.

The main critique of our study from the corn refiners association is based on their assertion that fructose and glucose are the same when in fact its textbook knowledge that their metabolic fate/pathways are very different. The CRA now says that sucrose and HFCS are “almost identical”. Almost identical acknowledges that they are different in some way which they are. Its a fact that HFCS-55 has at least 10% more fructose than sucrose and our prior study in which we analyzed popular beverages showed this was on average 20% and in some cases as much as 30% higher fructose. The key question in my mind is whether the additional fructose in HFCS is enough (even if its only 10% higher) to tip the balance towards the negative metabolic effects of fructose on health. This is at the heart of the issue and should be the focus of investigation. Our study, with its accepted limitations, adds to the growing body of evidence that the additional fructose coming from HFCS may indeed be enough to tip this balance.

His second message:

Thanks for responding, and yes, I’d be pleased if you added this to your blog –  – I think this will be a good addition. The question of whether the extra 10% fructose matters is indeed critical.

We also by the way did analyze total sugars versus diabetes in a much larger data set of 200 countries but the reviewers asked for that to be taken out which we did because we also thought the focus on HFCS would be unique. We also did see a clear relationship between total sugar and diabetes – some of that relationship was mediated by obesity but there also was an independent association between total sugars and diabetes. So, I agree – – both obesity and total sugars contribute to diabetes – – but I also believe, as shown in our paper, that HFCS has a separate link, and that this is probably due to the higher fructose content in HFCS.

Also, you mentioned in your blog that the different estimates of diabetes gave different results. That’s not really correct. The estimates of diabetes were different from each other, but regardless of which diabetes estimate we used, we still found a consistent association between HFCS and the 2 prevalence estimates of diabetes as well as fasting glucose. So in essence the results were validated using different prevalence estimates of type 2 diabetes.

  • Cathy Richards

    Fascinating discussion.
    Of course, we are now examining the pine needles on the pine tree in the mixed tree forest, with fungi and animals and birds and wildflowers and winds and weather and spores and creeks and boulders. But, like minute amounts of arsenic, perhaps it is relevant to examine the pine needle.
    More likely we should all be spending more time in forests. Period.

    Thanks for the great post — as always!

  • In New Zealand HFCS is not popular or pervasive (yet), but diabetes rates (DM2) are high. Also, white sugar and white flour consumption was probably highest in the 1960s and 1970s. I don’t like HFCS and think that if it took of in NZ we would have a worsening of the situation, but it hardly explains metabolic disease in a global context.

  • Travis

    I really don’t think sugar is the problem at all, and subscribe to Dr. Ray Peat’s philosophy on PUFA being the real culprit in diabetes and metabolic syndrome.

    “Glucose and insulin which allows glucose to be used for energy production, while it lowers the formation of free fatty acids, promote the regeneration of the beta cells. Although several research groups have demonstrated the important role of glucose in regeneration of the pancreas, and many other groups have demonstrated the destructive effect of free fatty acids on the beta cells, the mainstream medical culture still claims that “sugar causes diabetes.” —Ray Peat, PhD

    “When a normal person, or even a “type 2 diabetic,” is given a large dose of sugar, there is a suppression of lipolysis, and the concentration of free fatty acids in the bloodstream decreases, though the suppression is weaker in the diabetic (Soriguer, et al., 2008). Insulin, released by the sugar, inhibits lipolysis, reducing the supply of fats to the respiring cells.” —Ray Peat, PhD

  • JR

    The sugar/HFCS industry wants us to be confused about the niggling differences between the two, and you are (wittingly or unwittingly) aiding them. Diets high in sugar/HFCS cause diabetes and obesity. The science is clear. The question is not “which is more harmful?”. It is “why would anyone eat foods high in sugar or HFCS?”. They both make us sick. The longer that the purveyors of HFCS promulgate the false comparison with sugar, and web sites like yours support them, the more people will become sick from consuming sugar and HFCS. You need to report on the basic science – sugar, HFCS and refined carbs make us sick. The minuscule differences between the toxicity of these compounds masters little. It’s like arguing over what is worse, arsenic or cyanide…

  • Is there not consensus that reducing intake of high sugar beverages regardless of their source, should be the goal–both for weight management and type 2 diabetes prevention? We certainly don’t regulate caloric intake well with high intake of beverages such as soda and juices.

  • Peggy Holloway

    Correlation does not equal causation – correct. And obesity is correlated with diabetes, which does mean that diabetes is caused by obesity. It is more correct to say that both obesity and diabetes are symptoms of insulin resistance/carbohydrate intolerance. And yes, diets high in sugars, especially fructose (which includes both table sugar and HFCS) contribute to both obesity and diabetes in those who have underlying insulin resistance. That is a large percentage of the human population, thus the high obesity and diabetes rates we are seeing in countries where diets are based on grains and sweetened, processed food and low in fat.

  • Thomas Anderson, Ph.D.

    Some of the most ignored studies in the literature are those which have found dairy fats to be strongly protective against diabetes — rates of which have climbed as whole milk has been replaced by low-fat or skim and butter has been replaced by margarine.

    Along with these studies we have stats showing significant declines in milk consumption among children during the same time period that soft drink consumption has risen. This suggests to me that it might be possible to stop the diabetes epidemic in its tracks if we would only go back to whole milk and real butter.

    We should all know by now that “low fat” is nothing more than a monstrous scam based on marketing, not science, and only by reversing these disasterous trends do we have any hope of ever lowering our rates of diet-induced disease.

  • Prof Nestle,
    I subscribe to your logic over Dr. Goran’s conclusions.

    Why not talk more about calories and macro trends and less about these details of nutritional science that appear to be more about ‘being right’ than improving health outcomes?

    That seems, to me at least, like a better use of precious research funding but what do I know?

  • Joe

    Interestingly the American Diabetes Association points out that being overweight does not cause diabetes as most who are over weight never develop the disease (Their words not mine) and that eating too much sugar is not a cause of diabetes either (Again their words)

    Could it be that diseases thought to be related to diet and lifestyle are just natural phenomenon? Thus the conundrum of why certain people get diabetes, heart disease, cancer etc. and others do not who seemingly should based on lifestyle factors.

    So rather than play a version of health and nutrition twister looking for the best diet for the longest life realize that even the longest life ends in death. That is not said to be morbid but to point out that there is nothing we can do to thwart the natural process of things.

  • Chris

    Is obesity and total sugar consumption likely far more important to diabetes prevention than which sugars dominate a food supply? Sure.

    But is that a reason to downplay or even dismiss a study that demonstrates a possible link between HFCS and the disease? I don’t think so.

  • Food Lover

    The latest sugar-cereal commercial:

    Healthy-and-happy-looking children with nothing in the way of their dreams!! Eating sugar-cereal, playing sports, and doing well in school!!


    Correlation does not equal causation, and it is important for research to adhere to this fact. But, if marketers and ad campaigns want to simply suggest differently, I have no moral qualms about that. Fight concentrated gains and dispersed costs by appealing to the emotion of the masses, just as the BigFood and the rest of the “profits before health” companies do. I ask you, have simply providing the facts worked against lobbyists and rich industries in the past?

  • Cathy Richards

    Hey Marion, lots of doubter and flame tossers in this post! You wrote an excellent summary of the research and rebuttals and included clarifications and questions. Exactly what you should be doing. The research was not instigated by you, but it made the media, and you helped us see the politics behind it. Rock on Marion!

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  • Brad

    Didn’t see one comment that began with these words: I’m diabetic.

    I am – diabetic that is – and I attempt to avoid products that contain HFCS and I didn’t need this study to tell me that’s what I should do. I also attempt to avoid products that contain ANY highly processed sugars regardless of the source they were extracted from (corn, sugar beets, sugar cane, almost any fruit, and milk) or their chemical construction (fructose, sucrose, glucose, lactose).

    Moreover, the best book I’ve read on dealing with my diabetes didn’t attempt to blame me or what I ate or my life-style as the reason I am diabetic. First and foremost the primary reason I’m diabetic is that I have the correct — or maybe I should say the incorrect — genes.

    Until food and disease researchers, who from my perspective mostly seem to be just bad statisticians, can separate the people with the right genes from the people with the wrong genes, their “statistical” correlations are just so much high fructose bs.

    Moreover, the real kicker in the article seems to have gone uncommented on. That is the statement that diabetes in the U.S. cost $174 billion per year in 2007. The authors then claim that the 20% increase in diabetes that they correlated to HFCS increased health care cost in the U.S. by $95 million per day. Follow the money.

    I remember years ago reading about each new study that determined that injecting rats with high levels of — you name the substance — caused cancer. And, for years, the American Cancer Society continued to fund studies based on injecting high amounts of various substances into rats. Low and behold nearly all of those studies concluded that whatever substance they chose to inject into those rats at a high enough level would cause cancer. All the while the obvious answer was staring them in the face: almost any substance injected into a rat in a sufficent quantity would likely cause cancer. Hence my decsion to never give money to the American Cancer Society.

    To me, Dr. Goren and his colleagues appear to be no more than the rat and cancer reaseachers of their time.

  • Just a point of clarification: I was given permission to break the embargo on reporting about the study by its authors after the Corn Refiners Association broke it by releasing their rebuttal.

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  • Lisa Lucas Talbot

    Thanks for posting Dr. Goran’s comments about the important work he and his colleagues are doing. I appreciate his care in responding and trying to be very clear about their investigative issues and methods.

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