Over the past couple of weeks there have been numerous articles in the blogosphere that state, with a few variations, that high fructose corn syrup is addictive as cocaine. Wow, that’s quite a statement. In fact, one article, High-Fructose Corn Syrup “as Addictive as Cocaine”, doesn’t even make any caveats to that statement. They simply conclude that, “similar to cocaine addiction, the researchers say that some people are more vulnerable to food addiction than others, which explains why some are obese and some are not.” Setting aside the fact that food addiction is an eating disorder with a psychological basis, and more often than not includes foods that don’t contain high fructose corn syrup (HFCS), let’s look at the study that seems to have caused this myth that it is as “addictive as cocaine.”
Before we examine the article that is the basis of these claims, let’s find out a bit more about HFCS. But first, we need a little sugar biochemistry just to give the reader some background. There are two broad types of sugars, aldose and ketose, along with over twenty individual, naturally-found sugars, called monosaccharides. Of all of those sugars, only four play any significant role in human nutrition: glucose, fructose, galactose, and ribose (which has a very minor nutritional role, though a major one as the backbone of DNA and RNA). Got that? Four sugars. Whatever you eat, however you consume it, you can only absorb 4 sugars.
But it gets a bit more complicated. Many sugars form disaccharides that are compounds made of two monosaccharides covalently bound together. Table sugar, the white stuff in our sugar bowls, is sucrose that is a one molecule of glucose bound to one molecule of fructose. Sucrose is also the main sugar in most commercially purchased sugars that you find including brown sugar, molasses, beet sugar, and maple sugar (and syrup). Milk sugar is lactose, which is glucose and galactose, maltose is two glucose molecules, and there are a few dozen less common ones. Each has a slightly different taste, and some rare ones provide unique tastes to certain fruits and vegetables.
Before we can continue onto our discuss about HFCS you need to know one important thing. Humans can only absorb monosaccharides like glucose, fructose, galactose and ribose. In other words, all of those disaccharides and polysaccharides must be broken down into the constituent monosaccharide before it has any usefulness for a human. The gut has a variety of different enzymes that break down these starches and disaccharides–so sucrose cannot be absorbed, but it is broken down by sucrase into glucose and fructose, then absorbed. By the way, any disaccharide or polysaccharide that isn’t broken down remain in the gut, providing food for our gut bacteria, thereby maintaining a healthy digestive system.
Fructose is 1.73 times more sweet than sucrose despite having the same exact caloric content. So technically, you could use about 58% less fructose than sucrose to get the same sweetness. And any food that has more fructose (like honey, pears and grapes) will taste sweeter, even though it has no additional calories.
HFCS consists of 24% water, and the rest fructose and glucose. There are two main types of HFCS, HFCS 55 (used mostly in soft drinks) which is approximately 55% fructose and 42% glucose; and HFCS 42 (used in other types of beverages and processed foods), which is approximately 42% fructose and 53% glucose. There is another type, HFCS-90, approximately 90% fructose and 10% glucose, which is used in small quantities for specialty applications (interestingly, low calorie drinks, because, for the same sweetness about 33% less calories are added), but it is primarily blended with HFCS 42 to make HFCS 55. And despite the fact that HFCS is produced from corn, it is contains the same fructose and glucose that is found in table sugar, or any other plant in the world. Fructose and glucose do not chemically differ in any way from fructose and glucose found anywhere else, it is a fixed chemical structure. HFCS is used in some foods because of cost. For the equivalent sweetness as sucrose (cane sugar for example), the manufacturer can use less with fewer calories. Given that HFCS contains both natural fructose and natural glucose, and it is just as sweet with fewer calories, you’d think that people would be all over that.
I hope that’s clear. HFCS is nothing more than a syrup that contains a higher ratio of “natural” fructose to “natural” glucose than table sugar.
So, let’s get back to the article that started this whole thing. And this is where critical thinking skills are necessary, because the article doesn’t lend credence to the hypothesis that HFCS is as addictive as cocaine. The article is entitled, “Operant intraoral self-administration of high fructose corn syrup in laboratory rats,” by AnneMarie Levy, Cheryl Limebeer, Justin Ferdinand, Ucal Shillingford, Linda Parker, and Francesco Leri. I usually link to the article, because some of you like reading the original research, but it’s not directly linkable–I will cut and paste the whole thing right here:
The similarities between obesity and drug dependence suggest the hypothesis that “addiction” can develop to food. This hypothesis leads to the prediction that some foods may be “abused” because they are effective in reinforcing behavior leading to their consumption. The current studies in male Sprague-Dawley rats were designed to explore the reinforcing effect of high fructose corn syrup (HFCS); a sweetener associated with overeating and obesity. To this end, a novel method of operant intraoral self-administration (IOSA) was developed. Rats (n=22) received one daily 3-hour IOSA session, whereby responses on a sweetener-paired lever were reinforced by a discrete intraoral infusion of HFCS (25%, 90 µl/inf). Following 3 weeks of IOSA, substitution tests were performed to assess whether operant behavior maintained by HFCS would persist if it was substituted for the non-nutritive sweetener saccharin (0.1% w/v, 90 µl/inf). Using identical procedures, acquisition of IOSA of saccharin was also assessed in a separate group of rats (n=22). It was found that rats acquired and maintained IOSA of HFCS, but not saccharin. In addition, bingeing behavior developed during the initial 90 minutes of access to the solution, but only in rats that self-administered HFCS. A taste reactivity study, and analysis of food intake, suggested that HFCS was self-administered because of its post-ingestional consequences. These data indicate that HFCS has reinforcing properties, and that intraoral self-administration of HFCS can be used to characterize the effects of this sweetener on addictive behaviors.
You see, this isn’t an actual published article, it was a “poster presentation” at the Canadian Neuroscience Meeting 2013. As a poster presentation, it hasn’t been peer-reviewed, and it isn’t indexed by the major scientific publication systems like PubMed or Medline. The study hasn’t been confirmed by other research. The study hasn’t been critiqued or examined by other researchers in the field.
But let’s look at the study as presented, which lacks a boatload of information that is necessary to really evaluate it:
- We have no idea if this study is applicable to humans. In fact, it is merely observational at this point, before we can create a hypothesis relevant to humans, then test that hypothesis in a randomized, controlled clinical trial.
- The numbers of rats used were small; n=22 for the HFCS group, n=22 for the “control group.”
- We have no idea about the specific type of rats used, as there is some variability of behavior and health between different strains of rats.
- I simply cannot get a handle on how one could conclude “addiction” based on an animal choosing a solution that contains nutritional value (sugar, despite all the claims made, provides energy, and an animal would prefer it). But more than that, the control group was given saccharin, which has no nutritive value. If the author had set up an experiment that had a control group with different types of sugar, and those control rats behaved differently than the HFCS rats, this would be compelling data. And there’s strong evidence that rats prefer high fructose because of its sweetness factor, rather than any behavioral change.
- There needs to be a dose-response study, which would examine how different doses of the HFCS changes behavior. An increase in addictive behavior as the dose of the drug (or in this case, HFCS) is increased would be compelling evidence to support the hypothesis.
- Since this is an abstract from a poster presentation, we have no insight into the statistical strength of the differences between the two groups in this oversimplified and weak study.
- And finally, I still can’t believe that anyone would take a conference abstract and build a headline that there’s some “proof” that HFCS is as addictive as cocaine. On the hierarchy of high quality scientific research, with secondary meta-reviews published in high impact journals (Cochrane Reviews are amongst the best at this high quality research) sitting at the very top, then conference abstracts would be at or near the bottom, just slightly above non-peer-reviewed articles published in low impact, pay-to-publish journals. The value of this study, once again, is nothing more than observational, without any ability to determine if it has any scientific relevance at all. It certainly provides precisely no evidence that HFCS is as addictive as cocaine to a human.
Given the poor design of the research, which provides us with results that are mostly useless in developing a conclusion or even providing evidence in support of a hypothesis, how can anyone use this study as a support for anything? I would love to provide you with evidence that this has been studied, but I found no one who has studied it. Maybe this study by Levy et al. is paradigm shifting, and we are watching a whole new hypothesis linking HFCS and addiction behavior. But sometimes, the absence of evidence does mean evidence of absence, especially when you look for it, and until someone actually does some good research that’s published in an important journal, we just cannot accept the hypothesis, or even that there is “compelling evidence” in support of the hypothesis.
It’s clear that there are individuals want to “prove” that HFCS is unsafe and causes all sorts of problems. But HFCS is a sugar syrup, close to honey in ratio of fructose to glucose. Just because it has this scary chemical name, high fructose corn syrup, people must think that it’s made up of some evil fructose chemical. But all fructose molecules are exactly the same, whether it’s in honey, a fruit, maple syrup, cane sugar, or HFCS. Trying to invent a claim that it’s addictive, using very poor research, and without adequately explaining to the world how a fructose:glucose ratio, barely different than found in some other sweet “natural” foods, has some physiological effect, is just plain bad science.