Doubts regarding research suggesting that “A Very Sugary Diet Makes You Stupid”

Read the article(s):
http://www.medicalnewstoday.com/articles/245531.php
http://newsroom.ucla.edu/portal/ucla/this-is-your-brain-on-sugar-ucla-233992.aspx

I have some doubts about the conclusions reached in this research.

“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.”

Maybe, rather than omega-3 fatty acids negating a negative effect of fructose on synaptic activity, omega-3 combined with fructose may have enhanced activity and protected from damage to the synapses, leading to the rats’ increased performance in the maze tests.

“Our findings suggest that consuming DHA regularly protects the brain against fructose’s harmful effects …”

The researchers appear to have arrived at the conclusion that fructose (in abundance?) may have negative effects on cognitive activity and memory. I don’t believe that the results of this experiment necessarily point to this conclusion.

Both groups of rats were fed fructose, with the second group also being fed omega-3 fatty acids in the form of flaxseed oil and docosahexaenoic acid (DHA)
There should have been a further control group which was not fed fructose at all, to compare the other two groups against. This would determine whether fructose had any effect on the rat’s brain and performance in the maze tests, prior to investigating any effect that omega-3 fatty acids may have in “negating” this effect. Instead, the researchers gave fructose solutions to both groups of rats.

The UCLA article also suggests that the first group of rats, who did not receive omega-3 fatty acids, may have developed a resistance to insulin:  

"The DHA-deprived rats also developed signs of resistance to insulin, a hormone that controls blood sugar and regulates synaptic function in the brain. A closer look at the rats’ brain tissue suggested that insulin had lost much of its power to influence the brain cells."

"He suspects that fructose is the culprit behind the DHA-deficient rats’ brain dysfunction. Eating too much fructose could block insulin’s ability to regulate how cells use and store sugar for the energy required for processing thoughts and emotions."

I believe that this is the more appropriate route for the experiment to proceed. However, it is unclear whether it is fructose itself that is responsible for the DHA-deprived rat’s lower performance, or an interaction between insulin and fructose in the absence of omega-3 fatty acids.

More research should be done to determine an effect of fructose on the rats’ brain and performance, compared against a baseline, control group of rats who are not fed fructose solutions.

Nonetheless, it is known that omega-3 fatty acids protect the brain and enhance cognitive function and memory. However, it is not correct to conclude from this article that fructose has any negative effect on the brain.