Sugar makes you stupid
The study, published in the Journal of Physiology, is the first to show how a diet steadily high in fructose slows the brain, hampering memory and learning and how omega-3 fatty acids can counteract the disruption. "Our findings illustrate that what you eat affects how you think," said 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. "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 can minimise the damage."
While earlier research has revealed how fructose harms the body through its role in diabetes, obesity and fatty liver, this study is the first to uncover how the sweetener influences the brain. The UCLA team zeroed in on high-fructose corn syrup, an inexpensive liquid six times sweeter than cane sugar, that is commonly added to processed foods, soft drinks, condiments, and baby food. "We're not talking about naturally occurring fructose in fruits, which also contain important antioxidants," explained Gomez-Pinilla. "We're concerned about high-fructose corn syrup that is added to manufactured food products as a sweetener and preservative."
The team studied two groups of rats that each consumed a fructose solution as drinking water for six weeks. The second group also received omega-3 fatty acids in the form of flaxseed oil and docosahexaenoic acid (DHA), which protects against damage to the synapses - the chemical connections between brain cells that enable memory and learning. "DHA is essential for synaptic function - brain cells' ability to transmit signals to one another," Gomez-Pinilla said. "This is the mechanism that makes learning and memory possible. Our bodies can't produce enough DHA, so it must be supplemented through our diet."
Six weeks later, what the researchers saw surprised them. "The second group of rats navigated the maze much faster than the rats that did not receive omega-3 fatty acids," Gomez-Pinilla said. "The DHA-deprived animals were slower, and their brains showed a decline in synaptic activity. Their brain cells had trouble signalling each other, disrupting the rats' ability to think clearly and recall the route they'd learned six weeks earlier." The DHA-deprived rats also developed signs of resistance to insulin, a hormone that controls blood sugar and regulates synaptic function in the brain. "Because insulin can penetrate the blood-brain barrier, the hormone may signal neurons to trigger reactions that disrupt learning and memory," Gomez-Pinilla said.
He suspects that fructose is the culprit because eating too much of it could block insulin's ability to regulate how cells use and store sugar for the energy required for processing thoughts and emotions. "Insulin is important in the body for controlling blood sugar, but it may play a different role in the brain, where insulin appears to disturb memory and learning," he said. "Our study shows that a high-fructose diet harms the brain as well as the body. This is something new. Our findings also 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."