bad science

HFCS Follow-up: What the Rats at Princeton Can and Can’t Tell Us

Posted by Margot | Filed under:
Mar 29 2010

Ed called my attention to last week’s press release about the study at Princeton currently getting some mass media attention. The press release claims:

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. 

i know it's a squirrel, not a rat. apparently no one's gotten a rat to do this and then circulated it with the right keywords to match my google search. this image likely not original to: http://ybfat101.com/notyourfault.shtmlThat’s pretty surprising, given that other studies have suggested that there is no difference between HFCS and sucrose. The Princeton study doesn’t offer a definitive explanation for the difference they found, but they suggest that it may have something to do with the slightly greater proportion of fructose in the HFCS.

As I noted in the first post on high-fructose corn syrup, HFCS-55, which is the kind used in soft drinks and the Princeton study, has roughly the same proportions of fructose and glucose as table sugar. Table sugar, or sucrose, is composed of fructose bonded to glucose so it’s a perfect 50-50 split. HFCS-55 contains 55% fructose, 42% glucose, and 3% larger sugar molecules. There’s a lot of evidence that fructose is metabolized differently than glucose, and may promote the accumulation of fat, especially in the liver and abdomen. Indeed, that’s why I believe that agave nectar is probably nutritionally worse than table sugar. Still, I’d be pretty shocked if a 5% increase in fructose could produce a statistically significant difference in weight gain, unless the rats were eating nothing but sugar-water. And they weren’t—in both of the experiments reported in the original study, the rats had access to unlimited “standard rat chow,”

Experiment 1: Rats Who Binge?

In the first experiment, 40 male rats were divided into four groups of ten. All of them had 24-hour access to rat chow and water. Group 1 was the control, so they just had chow and water. Group 2 had 24-access to an 8% solution of HFCS (.24 kcal/mL), which the press release claims is “half as concentrated as most sodas”. Group 3 had 12-hr access to the same HFCS solution. And Group 4 had 12-hr access to a 10% solution of sugar dissolved in water (.4 kcal/mL), which the press release claims is “the same as is found in some commercial soft drinks.” The two things of note so far are that none of the rats had 24-hr access to sucrose-sweetened water, and that the concentration of the sucrose was nearly 2x that of the HFCS syrup.*

Why the 24 hr vs 12 hr groups? According to the study:

We selected these schedules to allow comparison of intermittent and continuous access, as our previous publications show limited (12 h) access to sucrose precipitates binge-eating behavior (Avena et al., 2006).

In other words, they fed the sucrose group on a schedule that they already knew would cause binging. And they didn’t include a 24-hr sucrose group to control for that.

That helps to explain the results: the rats that had 24-hr access to HFCS-water gained less weight than either the rats who had 12-hr access to sucrose-water or the rats that had 12-hr access to HFCS-water. So according to the experiment, it’s better to consume some HFCS than it is to binge on sugar (not, obviously, how they chose to frame it in either the formal write-up or the press release).

Princeton rats

The only difference between the four groups in the first experiment that was statistically significant at a p<0.05 was between the rats who got chow only and the rats who got 12-hr HFCS. There was no statistically significant difference between the rats who had 12-hr access to sucrose-water and the rats who had 12-hr access to HFCS-water. There wasn’t even a significant difference between the rats who had 24-hr access to HFCS-water and the chow-only rats. So the only basis for the claim in the press release that HFCS is worse than sucrose is the fact that the rats with 12-hr HFCS got a “significant” amount fatter while the 12-hr sucrose rats didn’t. Even though the 24-hr HFCS rats didn’t either.

I am not the only one who’s picked up on this—both Marion Nestle (a vocal critic of the food industry) and Karen Kaplan (not, as far as I can tell, a shill for the Corn Refiners Association) also dispute the claim that this research demonstrates anything conclusive about HFCS vs. sucrose. The lead researcher replied to Nestle’s post, and rather than addressing the discrepancy between the 12-hr and 24-hr HFCS groups, he merely corrects her assumption that the 24-hr rats should be fatter:

There have been several studies showing that when rats are offered a palatable food on a limited basis, they consume as much or more of it than rats offered the same diet ad libitum, and in some cases this can produce an increase in body weight. So, it is incorrect to expect that just because the rats have a food available ad libitum, they should gain more weight than rats with food available on a limited basis. –Bart Hoebel

Which just makes it all the more baffling why they didn’t include a 24-hr sucrose group. Additionally, according to their results, binging or “consuming more” doesn’t explain the results, because:

There was no overall difference in total caloric intake (sugar plus chow) among the sucrose group and two HFCS groups. Further, no difference was found in HFCS intake and total overall caloric intake in the groups given 12-h access versus 24-h access. Both groups consumed the same amount of HFCS on average (21.3±2.0 kcal HFCS in 12-h versus 20.1±1.6 kcal HFCS in 24 h), even though only the 12-h group showed a significant difference in body weight when compared with the control groups.

The only explanation they offer for these results is the slight difference in the amount of fructose the rats in the HFCS and sucrose groups consumed. But even that relies on the idea that the HFCS rats did not feel as satisfied by their sugar water and compensated by eating more:

…fructose intake might not result in the degree of satiety that would normally ensue with a meal of glucose or sucrose, and this could contribute to increased body weight.

Unless satisfaction itself makes rats thinner. Read more

Salt Headlines That Make The Vein In My Forehead Throb

Posted by Margot | Filed under:
Jan 27 2010

Salt has been all over the news this week because of a study just published in The New England Journal of Medicine claiming that if everyone in the U.S. reduced their sodium consumption by 3 grams/day, there would be 32,000 fewer strokes, 54,000 fewer heart attacks, and 44,000 fewer deaths every year. The story that got my attention was:

Remaining Arctic Ice Seen Melting Away Completely! (...on a computer screen)

That’s surprising, I thought. Everything I’ve read suggests that the relationship between salt consumption and cardiovascular disease is weak, inconsistent, and probably only valid for 20-30% of the population. So I expected the article to refer to some new research where, you know, “big benefits” were “seen.” As in observed. Like, in the world. And, given the claim about the magnitude, probably also measured.

To their credit, the authors of the study claim no such thing. The numbers are projections based on the application of several assumed effects of salt reduction, adjusted for different demographics and then applied to a model of the entire U.S. population. Thus, the title of the study: “Projected Effect of Dietary Salt Reductions on Future Cardiovascular Disease.”

The article seems to grasp the essentially speculative nature of the findings. The very first sentence uses the conditional tense:

…scientists writing in The New England Journal of Medicine conclude that lowering the amount of salt people eat by even a small amount could reduce cases of heart disease, stroke and heart attacks as much as reductions in smoking, obesity, and cholesterol levels.

The headline, on the other hand, seems to have confused the “scientists” with clairvoyants. Never mind doing any checking into the validity of their assumptions.

And the claim about how the benefits compare to smoking and obesity reduction led to a few headlines like this:

webmd salt

This crazypants idea initially sounds a lot like what the study’s lead author claims:

"The cardiovascular benefits of reduced salt intake are on par with the benefits of population-wide reductions in tobacco use, obesity, and cholesterol levels."

But the logic behind the claim is that a small improvement in the health of every single American would be as significant as a large health improvement in the health of every single smoker:

Dr. Bibbins-Domingo said that for many people the decrease in blood pressure would be modest, which is why, she said, “many physicians have thrown up their hands and said, ‘I’m not going to advise my patients to reduce salt because it’s too hard for patients and the benefits for any individual are small.’

“But small incremental changes in salt, such as lowering salt in tomato sauce or breads and cereals by a small amount, would achieve small changes in blood pressure that would have a measurable effect across the whole population,” she said. “That’s the reason why this intervention works better than just targeting smokers.”

For any given individual, there is no question about whether cutting salt is even close to “as good” as quitting smoking. The evidence for the link between smoking and lung cancer and death is strong, reliable, consistent, and has a clear causal mechanism (carcinogens). The link between salt and cardiovascular disease and death is weak, inconsistent, and still poorly understood.

That latter point starts to get at the problems with the study itself, and not just the headlines it inspired. A number of the assumptions the projection was based on are either demonstrably false or simply unsubstantiated. More on this some other time; for now, a few quotes and links to the essays they come from in Esquire and the medical journal Hypertension:

In a more recent statement, the founder of the American Society of Hypertension, Dr. John Laragh, goes further: "Is there any proven reason for us to grossly modify our salt intake or systematically avoid table salt? Generally speaking the answer is either a resounding no, or at that, at best, there is not any positive direct evidence to support such recommendations."

…

Studies show that 30 percent of the Americans who have high blood pressure would greatly benefit from a low-sodium diet. But that's about 10 percent of the overall population -- the rest of us are fine with sodium. And drastically cutting out sodium may actually hurt some people. ( "Go Ahead, Salt Your Food")

And:

The available data suggest that the association of sodium intake to health outcomes reflected in morbidity and mortality rates is modest and inconsistent. Therefore, on the basis of the existing evidence, it seems highly unlikely that any single dietary sodium intake will be appropriate or desirable for each member of an entire population.... The decision to adopt a low sodium diet should be made with awareness that there is no evidence that this approach to blood pressure reduction is either safe, in terms of ultimate health impact, or that it is as effective in producing cardioprotection as has been proven for some drug therapies. (Salt, Blood Pressure, and Human Health)