To function at its very best, the brain needs fat and sugar. That may sound surprising, given how often we're warned away from those two substances. However, the brain is the only organ that draws nearly all its energy from glucose. It's also the body's second-highest deposit of fat, after fatty tissue itself (such as the butt and the gut) [source: Aaronson].
It's not just any fat and sugar that the brain is after, though. Trans fats and saturated fats, such as those found in fast food and junk food, can decrease cognitive ability [source: UCLA]. One study found that rodents who were given the equivalent of rat junk food couldn't navigate mazes or remember the solutions to problems they'd solved previously [source: Douglas et al.]. Those kinds of fats harden brain cells.
Your brain cells crave polyunsaturated fatty acids, which you may know by the names omega-6 and omega-3. We typically get enough omega-6 acids throughout the day thanks to their presence in soy and corn oils, but most people need to consume more omega-3 fatty acids. These acids appear to strengthen the brain's synapses, which provide the pathways for neural communication. Omega-3s also appear to help molecules on the synapses directly related to learning and memory. In an Australian study, children who drank a beverage with omega-3 fatty acids received higher scores on tests of verbal intelligence and memory compared to children who didn't have the drink; results were evident after just six months [source: UCLA].
Omega-3 fatty acids are found in some nuts, such as walnuts and hazelnuts, flaxseed, kiwi and most importantly, fish. Researchers aren't sure why exactly fish are so helpful to brain cells, but there's plenty of evidence showing that it might be the ultimate brain food. In one study, elderly people who ate fish at least once a week slowed cognitive decline about 10 percent compared to those who didn't chow down on fish, and the fish-eaters also performed better on tests of memory and mental sharpness [sources: O'Connor, Bakalar]. In rodents, omega-3 deficiency has led to learning impairments, while the consequences of a deficiency in humans include brain disorders such as dyslexia and schizophrenia [source: UCLA]. One physiologist even speculated that fish consumption by early man is what spurred the human brain to get so big in the first place [source: Binns].
To read about the sugar your brain needs and to learn whether too much brain food is a bad thing, swim on over to the next page.