High Fructose Diet Not So

Sweet for the Brain

Fran Lowry | 24th May 2012

Diets high in fructose impair cognitive function, but this is reversed when the diet is supplemented with appropriate intake of omega-3 fatty acids, new research suggests. Although the study was done in an animal model, the findings have relevance for humans, coauthor Fernando Gomez-Pinilla, PhD, from the UCLA Brain Injury Research Centre, Los Angeles, California, told Medscape Medical News. “High fructose consumption can induce some signs of metabolic syndrome in the brain and can disrupt the signalling of the insulin receptors and reduce the action of insulin in the brain,” Dr. Gomez-Pinilla said. “On the other hand, consumption of omega-3 fatty acids, particularly decosahexanoic acid [DHA], seems to protect against the effect of this high fructose consumption. That was the most interesting thing for us, to find that these changes in the brain that the fructose was triggering, the poor learning and the other molecular changes, could be buffered by omega-3 fatty acids,” he added. The study is published in the May 1 issue of the Journal of Physiology. Dr. Gomez-Pinilla and coauthor Rahul Agrawal, PhD, fed adult male Sprague-Dawley rats standard rat chow for 1 week and then trained them on the Barnes maze test for 5 days to learn the test. The rats were then randomly assigned to receive an omega-3 fatty acid diet or an omega-3 fatty acid–deficient diet with or without fructose solution as drinking water for 6 weeks. They found that the rats assigned to the omega-3 fatty acid–deficient diet showed a significant memory deficit in the Barnes maze, which was further exacerbated by fructose intake. They also found that the omega-3 fatty acid–deficient diet, plus high fructose consumption, disrupted insulin receptor signalling in the hippocampus, a sign of insulin resistance. Rats that received the diet rich in omega-3 fatty acids navigated the maze much faster than those that did not receive omega-3 fatty acids. “The omega-3 fatty acid–deficient rats 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 had learned 6 weeks earlier,” Dr. Gomez-Pinilla said. Treatment Implications? Encouraged by the results from this study, Dr. Gomez-Pinilla said he is now planning to study how diet — namely, a diet deficient in omega-3 fatty acids — can affect certain brain disorders, including posttraumatic stress disorder (PTSD). “We have the idea that the type of diet we have described in the current study, one high in sugar and low in omega-3 fatty acids, may be a factor in PTSD,” he said. For example, such a diet is typical for military personnel, who also suffer a high rate of PTSD. “They typically consume a high caloric diet but one that is not high in the right nutrients. They are not consuming enough omega-3 fatty acids. DHA is essential for synaptic function, and this is the mechanism that makes learning and memory possible. “Our bodies don’t produce DHA, so it must be supplemented through our diet. Consuming omega-3 fatty acids regularly can protect the brain against fructose’s harmful effects,” “Amazing” Finding Bonnie Kaplan, PhD, from the University of Alberta, Calgary, Canada, said this study confirms that food containing high amounts of sugar adversely affects brain function. “High sugar affects synapses, and this study confirmed that. But then, the researchers showed a very interesting thing, that adequate omega-3 fatty acids provided a protective effect. The fact that eating an adequate amount of DHA protects our brain cells from what we already know to be the bad effect of an unhealthy dietary variable — that’s amazing!” Dr. Kaplan pointed out that children in North America commonly consume drinks high in fruit sugar and that many parents believe that fruit juice is somehow healthier than soda. “Probably they are not, and the children should go back to drinking water,” she said. “This is a very important study, and I was very excited to see it. They are a very good team at UCLA, and Dr. Gomez-Pinilla in particular has contributed a lot to this literature.” The study was supported by the National Institutes of Health. Dr. Gomez-Pinilla and Dr. Kaplan have disclosed no relevant financial relationships.