A recent study published in the prestigious Journal of Physiology has demonstrated that rats fed a diet high in fructose showed slowed brain function and trouble with nerve cells signaling each other as well as poor memories compared to the group of rats who were given a diet that included omega-3-fatty acids (found in high levels in most fish).
The fructose-dumb rats had significant difficulty navigating a maze they had learned 6 weeks prior to receiving the sugary diet. This information fits well with what we currently understand about the human brain in terms of the foods we eat. Most tissues and organs in the human body use glucose (simple sugar) for energy. Whatever we eat on a daily basis is broken down in our gut and liver to glucose, fat and protein. The glucose is used for energy and the fat is stored for times when there is no available glucose in the blood. Fat is then taken from its deposits in our body (love handles and big butts) and turned into glucose for the cells to use. It turns out that the human brain can and does use glucose for energy but actually is the only organ that would prefer to use the by-products of fatty breakdown (called ketone bodies) for energy.
So, simply put: the next time you go for that snickers bar, make sure you know what you have to do for the rest of the day or write it down. Your sugar high is doing your brain no favors!