This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
I did a post back in 2009 on High Fructose Corn Syrup (HFCS). In researching that post I dug hard into the chemistry of HFCS, the similarities and differences from sugar, and the current literature on whether it's coming for your waistline. At the time, I concluded that, while I know fructose on it's own isn't good for you, the data isn't yet convincing, and I as yet couldn't distinguish between the effects of HFCS, and the massive increase in our diets of sugars in general.
And now I've found this paper, and have been asked to cover the topic again. And...I could be convinced. But I'm not convinced yet and I'll tell you why.
(Source)
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Bocarsly, et al. "'High fructose corn syrup causes characteristics of obesity in rats: increased body weight, body fat and triglyceride levels". Pharmacology, Biochemistry, and Behavior, 2010.
This paper came out in 2010, and when it did, it generated a minor buzz. Everyone loves to hate on HFCS, and while many studies have shown that there is relatively little difference between HFCS and regular sugar (though there are some differences in metabolism, which I will get back to), the only real data we have so far to link to is that Americans as a whole are getting fatter, and we're all eating a lot of HFCS (except for those of us who don't, some Americans who can afford it are now opting out due to the very fears we are discussing).
And then, out came this paper. Some lauded it real proof of the evils of HFCS. Others (particularly people in the HFCS industry) criticized it as poor science with no real indications. Me? Well, I think it could be a bit of both.
So, what is HFCS? Well, table sugar is a combination of two monosaccharides, which are single molecule sugars, glucose and fructose. When you bring them together, they bond into a disaccharide, known and loved the world over as sucrose.
(Source. The O in the middle there is the linkage you're looking for)
HFCS is...basically sucrose. Except it's not. The most common formulation of HFCS is 55% fructose and 42% glucose (yes, that does not add up to 100%, there's a small amount of other stuff in there). This means that, while the fructose and glucose bond all they can, there is some fructose left over and floating about. And fructose is SWEETER than glucose. So a higher proportion of fructose to glucose makes for more free fructose and a sweeter drink. In theory. The reality is that the percentages aren't that different, and the sweetness of HFCS is pretty comparable. The big difference here is PRICE. HFCS is a heck of a lot cheaper than sucrose due to corn subsidies in the US from the government. This has made it much easier over time for companies producing processed foods to produce lower cost versions of those foods made with HFCS instead of sugar (I'm looking at you, Coca-Cola), and this means their profit margins can be higher. If you were a company, the siren song of HFCS would be hard to deny. And so it's become hard to avoid HFCS in some foods, especially foods that are prepared (HFCS is in your peanut butter, your jelly, and even your bread), and particularly so for those who can't afford the more expensive alternatives.
But of course, there might be a problem with HFCS. You see, Americans have this obesity epidemic going on. Our weights have increased a great deal in the last few years, and we want to know why, and preferably we want something nice and easy to make go away that we can point our fingers at. HFCS makes a good candidate for this, it became popular around the same time that Americans started getting fatter, it's all "unnatural" sounding, and it's something that would be relatively easy to make go away, definitely easier than changes to lifestyle and infrastructure.
But just because HFCS came out around the time Americans started getting larger doesn't mean HFCS is to blame. And HFCS is not the only thing that has increased recently, our entire world has become a lot sweeter, and a lot saltier, than it ever has before. It could be general changes in diet and habits. Correlation is not causation, after all. While it's easy to point fingers, people need actual PROOF that ingestion of HFCS causes increased weight gain.
And then along came this study. In this study, the authors looked at three conditions in which rats got to eat HFCS.
1) Male rats got 2 months of four different conditions. 12 hour or 24 hour access to HFCS with their chow, 12 hour sucrose with their chow, and just chow.
2) Male rats for 6 months of three different conditions. 12 hour or 24 hour access to HFCS with their chow, or just chow.
3) FEMALE rats got 7 months of four different conditions. 12 hour or 24 hour access to HFCS with their chow, 12 hour sucrose with their chow, and just chow.
They then looked at how much the rats weighed at the end, how much sweet stuff they consumed, and, in some cases, blood levels of triglycerides.
They found that male and female rats exposed to 24 hour HFCS with their chow gained more weight compared to chow alone, and after 6-7 months, male and female rats with 24 hour HFCS access had elevated levels of triglycerides. Finally, males and females after 6-7 months of 24 hour HFCS had heavier fat pad weights in their abdomens than those with access to chow.
HFCS MAKES YOU FAT!!!! WE ARE ALL GOING TO DIE.
Or at least, that's one interpretation.
While some immediately hailed this as the real proof we needed that HFCS and the corn industry were evil, others immediately called the results into question. I think both sides have something to be said for them. While the study DOES show increased weight gain, it's poorly grouped, all groups received different treatments (why six months for males and seven months for females?), and the results...are not very consistent. In their eight week treatment group, the 12 hour HFCS weight gain was HIGHER than the 24 hour HFCS weight gain, in the 6 month males the 12 AND 24 hour groups were higher, and in the 7 month females only the 24 hour group was higher. The 6 month males and the 7 month females had similar inconsistencies in fat pad levels, with males showing bigger fat pads after 12 hour access, and females only showing bigger fat pads after 24 hour access. Now, this could be the result of a sex difference between males and females, but I really think you can't parse that out without having similar treatment times and conditions, which they didn't have. Results continued to be really inconsistent for the triglycerides group.
Finally, the biggest criticism others made of the study (to my mind). The authors measured how much HFCS and sucrose were consumed in the first group, and found that the rats drinking sucrose were actually getting more calories from the drinks. BUT. They never measured total calorie intake. At all. And they never measured the HFCS and sucrose consumption in their long term animal trials at all. Now, it's not hard to see why, rats are messy eaters and it can be hard to determine how much chow is hitting the belly vs hitting the floor, but I think this is a pretty big issue. Some studies have shown that, as rats eat more sucrose, they compensate by eating less chow. Is this still true here? What about for HFCS? Were the rats consuming more or less calories TOTAL?
Now, I note up there that this is the biggest criticism others have made of the study. Me? I've got more. They looked at blood glucose levels for the first group, and not for the second two. I have to wonder why (especially since blood glucose levels are ridiculous easy to take). And secondly, I do believe that the rats eating the HFCS gained more weight. I definitely do. But the consistent results are only between the 24 hour HFCS condition and chow. When they looked a sucrose, they only looked at 12 hour access. Where IS that 24 hour sucrose condition? Would rats gain just as much weight? Inquiring minds want to know.
And finally, here's my biggest criticism. What is the mechanism. WHY does HFCS cause more weight gain? The authors of this study did not address this (the data is a little preliminary in that respect). The idea from other studies is that HFCS doesn't active feeding hormones such as leptin in the same way as sucrose does, and this means that you don't feel as full and you eat more (this is usually in studies with rats using just fructose, not really the same conditions, as fructose alone is rough in humans. Like diarrhea rough. They also got similar results with sucrose which the authors did not see here). But I don't see leptin levels here...and even if I did, WHY? HOW is this promoting abdominal obesity?
So basically, I do believe the rats gained more weight. I think it's clear enough. But I want to know if that's the HFCS, or high caloric consumption (by comparing it to the same sucrose access, a condition they didn't have). And I want to know HOW it's working. Do people (or rats) who have this HFCS condition have higher leptin resistance? Higher insulin resistance? What is the mechanism? Because a mechanism could really convince me that HFCS is TEH EVILZ. Until then, I believe what I have believed, that our world is just too sweet in general and our portion sizes too large, and that your Coca-Cola is too many calories, whether those calories are from HFCS, or from sugar.
But I'm willing to be convinced.
Bocarsly, M., Powell, E., Avena, N., & Hoebel, B. (2010). High-fructose corn syrup causes characteristics of obesity in rats: Increased body weight, body fat and triglyceride levels Pharmacology Biochemistry and Behavior, 97 (1), 101-106 DOI: 10.1016/j.pbb.2010.02.012