Earlier studies have shown that fructose is involved in causing diabetes, obesity and a fatty liver, but this is the first research to uncover how sugar can influence the brain. In the Americas, high fructose corn syrup is widely used, whereas in Europe and Asia sucrose is more prevalent; this study focused on fructose.
Fernando Gomez-Pinilla, a professor of neurosurgery at the David Geffen School of Medicine at UCLA and a professor of integrative biology and physiology in the UCLA College of Letters and Science said
"Our findings illustrate that what you eat affects how you think ... Eating a high-fructose diet over the long term alters your brain's ability to learn and remember information. But adding omega-3 fatty acids to your meals can help minimize the damage."
It is estimated that the average American consumes around 47 pounds of sugar and another 35 pounds of high fructose corn syrup per year. In the late 1800s, this figure was about 2 pounds per year. The soaring rates of diabetes, obesity and even cancer have been linked to a sugary diet. A part of the problem is the prevalence of sugar and high fructose corn syrup that is laced into everything from apple sauce, yoghurt and fruit juices to bread, ketchup - even hamburgers and processed meat often have sugar added. Avoiding sugar is not as simple as not drinking sodas and eating candy bars.
Gomez-Pinilla, who is also a member of UCLA's Brain Research Institute and Brain Injury Research Center, goes onto explain:
"We're less concerned about naturally occurring fructose in fruits, which also contain important antioxidants ... We're more concerned about the fructose in high-fructose corn syrup, which is added to manufactured food products as a sweetener and preservative."
To carry out the study, Gomez-Pinilla and his study co-author Rahul Agrawal, a UCLA visiting postdoctoral fellow from India, looked at two groups of rats. Both group was given drinking water laced with fructose solution, but the second group was also fed flaxseed oil and docosahexaenoic acid (DHA). These contain omega-3 fatty which are thought to protect against damage to the synapses, which are essentially the electrical connections between the brain cells.
As a control, the animals were fed on standard rat feed for five days before the fructose diet started. They were also trained on a maze twice per day and tested to see how well they performed. They also placed visual markers in the maze to help the rats remember their way around.
Gomez-Pinilla recounts his experience of testing the rats after six weeks on the sugary diet:
"The second group of rats navigated the maze much faster than the rats that did not receive omega-3 fatty acids ... The DHA-deprived animals were slower, and their brains showed a decline in synaptic activity. Their brain cells had trouble signaling each other, disrupting the rats' ability to think clearly and recall the route they'd learned six weeks earlier."
The rats that went without the fatty acids, also started to show insulin resistance. Gomez-Pinilla postulates that this is most likely the cause of the loss in memory, because insulin is involved in regulating how brain cells are able to use and store sugar for the energy required for processing thoughts and emotions. A diet high in sugar causes more insulin release and perhaps makes the cells become tolerant to the hormone, as they do with other hormones and drugs that are artificially introduced.
Gomez-Pinilla practices what he preaches, and says he maintains a diet low in sugar and high in fatty acids. He recommends taking one gram of DHA per day and eating foods like salmon, walnuts and flaxseeds that are rich in DHA. He concludes that:
"Our findings suggest that consuming DHA regularly protects the brain against fructose's harmful effects ... It's like saving money in the bank. You want to build a reserve for your brain to tap when it requires extra fuel to fight off future diseases."
The UCLA study was funded by the National Institute of Neurological Disorders and Stroke. Gomez-Pinilla's lab will next examine the role of diet in recovery from brain trauma.
Written by Rupert Shepherd