Don’t fret — the researchers figured out how to protect rats from these damaging changes.
If you’re a big soda drinker or have an insatiable sweet tooth, you’re probably consuming a lot of fructose — a sugar that’s common in the Western diet.
Americans get most of their fructose from foods that are sweetened with high-fructose corn syrup, sweetened drinks, syrups, honey, and desserts. The Department of Agriculture estimates that Americans consumed an average of about 27 pounds of high-fructose corn syrup in 2014.
Now, a study performed on rats at UCLA has unveiled some troubling findings about what fructose does to the brain.
A number of diseases — like diabetes, cardiovascular disease, Alzheimer’s, attention deficit hyperactivity disorder (ADHD), and more — are linked to changes to genes in the brain. The new study reveals that hundreds of these genes can be damaged by fructose in such a way that is characteristic of the above-mentioned diseases.
To come to these findings, the researchers trained rats to escape from a maze, and then randomly divided them into three groups. Over the next six weeks, one group of rats drank water with an amount of fructose that would be roughly equivalent to a human drinking a liter of soda per day, another group drank water without fructose, and a third group drank fructose water and ate a diet rich in DHA — an omega-3 fatty acid that the researchers hypothesized might reverse the damaging effects.
After the six weeks, the rats were put through the maze again, and the ones who only drank the fructose water navigated the maze about half as fast as the rats who only drank water, suggesting that the fructose had impaired their memories.
Amazingly, the rats that had been given the fructose with the DHA showed very similar results to those that had only drank water — indicating that DHA eliminated the harmful effects of fructose.
"DHA changes not just one or two genes; it seems to push the entire gene pattern back to normal, which is remarkable," Xia Yang, a senior author of the study and a UCLA assistant professor of integrative biology and physiology, said in a press release. "And we can see why it has such a powerful effect."
The researchers say that DHA occurs naturally in the membranes of our brain cells, but not in a large enough quantity to help protect us from diseases. DHA is mainly found in animal products like fish, eggs, and meats, with oily fish like wild salmon, mackerel, and herring being the richest dietary source of DHA.
Since our bodies are deficient in the machinery needed to naturally produce enough DHA, the researchers say it has to come from our diets.
In the study, the research team sequenced over 20,000 genes in the rats’ brains, identifying over 900 altered genes — over 200 in the hippocampus, the brain region that helps regulate memory and learning, and over 200 in the hypothalamus, which is the brain’s major metabolic control center.
The researchers report that the vast majority of the genes they identified, which are comparable to those in humans, interact to regulate metabolism, inflammation, and cell communication.
How exactly does the fructose manage to alter the genes? The scientists found that fructose either removes or adds a biochemical group to cytosine, which is one of the four nucleotides that make up DNA. This mechanism plays a critical role in turning genes “on” or “off,” the researchers say.
In addition to the above-mentioned diseases, Yang notes that alterations to the identified genes have been implicated in Parkinson’s disease, depression, bipolar disorder, and other brain diseases.
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However, the researchers did come across some good news. Of the 900 altered genes, the researchers found that two in particular — Bgn and Fmod — appear to be among the first that are affected by fructose. Once those genes are altered, they can “set off a cascade effect that eventually alters hundreds of others,” according to Yang.
This means that Bgn and Fmod are potential targets for new drugs to treat the diseases that are caused by altered genes in the brain.
Although consuming DHA appears to be beneficial, Yang says it’s “not a magic bullet for curing the diseases.” Future research will have to look into the extent of its ability to reverse damage to human genes.
"Food is like a pharmaceutical compound that affects the brain," concludes Fernando Gomez-Pinilla, professor of neurosurgery and of integrative biology and physiology, and co-senior author of the paper.
He recommends generally consuming less sugar and saturated fat, avoiding sugary soft drinks, and cutting down on desserts.
The results of the study are published in the journal EBioMedicine.
Editor's note (April 27): the article has been updated to emphasize the fact that the study was performed only on rats, not humans.