Mainly, I hope to bring a little more overall perspective to a study that, while perhaps could be valuable, has brought along with it unnecessary fears that a little hummingbird fuel, aka sugar, will make people walk around aimlessly as brainless as zombies. It's nonsense, of course, that sugar makes you stupid. After all, neurons run on a constant supply of glucose delivered by the bloodstream (as they don't store glucose as glycogen like other cells), a fact that several media reports completely failed to mention.
But my main grief with the press release and several subsequent reports, as well as quotes from the scientists themselves, is how they confuse readers by making a villain of high-fructose corn syrup (HFCS), especially its fructose moiety. (Ranging from the not-so-bad to horrible, there's this one - not so bad, this one, this one, this one, and, this one - horrible.) These articles simply play into the already common misconception that HFCS as a sweetener is somehow uniquely dangerous to health. The scare tactics may bring more hits and interest from readers, but it's poor health reporting.
Let's just point out again that HFCS is metabolically the same as sucrose (plain table sugar) -- they each are made up of almost equal amounts of glucose and fructose. HFCS's content of fructose is hardly "high" in comparison to other sugars; it may have been more appropriately called medium-fructose corn syrup. The fructose content is relatively similar (or less) to what's found naturally in honey, agave, and other natural sugars.
Now, a review of the study (1) from Journal of Physiology; if you read any of the articles linked to above, then you probably already know the story: UCLA researchers trained rats fed normal chow and drinking water on a maze twice daily for five days to establish a baseline. Then, they separated the rats into two groups and supplemented both groups' drinking water with fructose (15 percent) -- essentially, putting them all on a high-sugar diet that would, basically, lead to hyperglycemia and insulin resistance.
On to the interesting part of the experiment: The first group of rats received a diet deprived of omega-3 fatty acids. The second group, however, also received a supplement of omega-3 fatty acids (0.5 percent flaxseed oil and 1.2 percent docosahexaenoic acid (DHA)). Strong evidence supports that omega-3s, specifically DHA, is neuroprotective through a variety of mechanisms (with positive effects on inflammation and insulin resistance).
A quick note before we move on -- we already knew that giving mice a high-sugar diet leads to insulin resistance. Nothing new so far. We also knew that insulin resistance and hyperinsulinemia themselves can have large effects on the brain. What is well established is that metabolic syndrome, obesity, and diabetes all make animals and humans more vulnerable to mental illness. So, this study is not really about sugar. It's really about the possible role of omega-3s as a protective nutrient in a metabolic syndrome rat model.
So, what of the findings? After six weeks on the high-sugar diet, the DHA-deprived rats were slow and didn't do so well in the maze suggesting declines in neuronal signaling while the DHA-supplemented rats zipped through the maze without any troubles. Conclusion? Basically, the study showed DHA protects against disrupted insulin signaling in rats' brains.
What really bothers me: The headlines of media reports hardly touched the real news: "DHA protects brains of rats from effects of insulin resistance," which could eventually have implications in those with metabolic syndrome, diabetes, and obesity. Instead, the press release and articles mainly focused on the whole idea of winning readers by playing on already existing fears about HFCS and fructose. Moreover, fructose is made out to having a central role in causing "stupidity." Nevermind that other sources of carbs (e.g white flour) or calories (e.g. fat) eaten in excess would also lead to insulin resistance.
The scientific literature suggests no unique metabolic danger of fructose in humans versus other carbs that is quantitative. Consider the findings of a series of recent meta-analyses that reviewed randomized controlled isocaloric trials in humans by Sievenpiper et al (2, 3): fructose did not have any significant effect on body weight compared to other carbohydrate sources. In fact, at levels normally found in fruit, fructose could even support blood sugar control. That's quite the opposite of being unique in increasing risk of insulin resistance. The facts are that overconsumption in general of any carbohydrates or other sources of calories (mice fed a high-fat diet get insulin resistance, too) is the main problem when it comes to metabolic syndrome factors.
As argued by scientists at Experimental Biology 2012, it's time to stop playing the "blame game" when it comes to obesity and metabolic syndrome factors. There's nothing good that comes of demonizing a single ingredient whether it be HFCS, fructose, table sugar, or fat. It only leads people to switch and eat/drink too much of something else. The end result is still the same: obesity, insulin resistance, metabolic syndrome, and diabetes. Then, insulin resistance still ends up harming the brain (I played with the idea of titling this post "It's insulin resistance, stupid").
Don't get me wrong -- I cringe every time I see a child or adult ordering a large HFCS-sweetened soda from a restaurant or gas station. But, it's also frustrating to see the words "no high-fructose corn syrup" acting like a kind of "health halo" on high-calorie food products (like the marketing of a Starbucks Frappuccino containing nearly 25 teaspoons of table sugar). The majority of people do need to reduce consumption of sugar and overall calories, as well as exercise more, to help maintain a healthy weight, maintain or put on muscle, and improve their insulin sensitivity.
The message of this study and reports finally should have been simply, "Don't overeat because it leads to insulin resistance and brain trouble; and a new study in rats suggests DHA could offer protection if you do."
- Agrawal R and Gomez-Pinilla F. ‘Metabolic syndrome’ in the brain: deficiency in omega-3 fatty acid exacerbates dysfunctions in insulin receptor signalling and cognition J Physiol 590.10 (2012) pp 2485–2499. doi: 10.1113/jphysiol.2012.230078
- Sievenpiper JL, de Souza RJ, Mirrahimi A et al. Effect of Fructose on Body Weight in Controlled Feeding Trials: A Systematic Review and Meta-analysis. Ann Intern Med 2012;156:291-304.
- Sievenpiper JL, Chiavaroli L, de Souza RJ et al. 'Catalytic' doses of fructose may benefit glycaemic control without harming cardiometabolic risk factors: a small meta-analysis of randomised controlled feeding trials. Br J Nutr 2012;1-6. doi: 10.1017/S000711451200013X