We know that the foods we eat affect the body. But they may have even more of an influence on how the brain works -- it's general tone and level of energy and how it handles its tasks. Mood, motivation and mental performance are powerfully influenced by diet.

The brain is an extremely metabolically active organ, making it a very hungry one, and a picky eater at that. It's becoming pretty clear in research labs around the country that the right food, or the natural neurochemicals that they contain, can enhance mental capabilities -- help you concentrate, tune sensorimotor skills, keep you motivated, magnify memory, speed reaction times, defuse stress, perhaps even prevent brain aging.

The Right Fats

Evidence is accumulating that a diet that draws heavily on fatty food and only lightly on fruits and vegetables isn't just bad for your heart and linked to certain cancers. It may also be a major cause of depression and aggression. Such a diet is particularly common among men.

The health of your brain depends not only on how much (or little) fat you eat but on what kind it is. Intellectual performance requires the specific type of fat found most commonly in fish, known as omega-3 fatty acids. Even diets that adhere to commonly recommended levels of fats, but the wrong kind, can undermine intelligence. What makes this finding awkward is that certain oils widely touted as healthy for the heart are especially troublesome for the mind.

Omega-3s are known to be particularly crucial constituents of the outer membrane of brain cells. It is through the fat-rich cell membrane that all nerve signals must pass. In addition, as learning and memory forge new connections between nerve cells, new membranes must be formed to sheathe them. All brain cell membranes continuously need to refresh themselves with a new supply of fatty acids. A growing amount of research suggests that the omega-3s are best suited for optimal brain function.

While consuming too much fat overall and too much saturated fat, many North Americans fail to consume enough omega-3s. And the polyunsaturated oils widely recommended as healthful for the heart and widely used in cooking, frying and prepared food -- corn, safflower and sunflower oils -- have almost no omega-3s. Instead they are loaded with omega-6s. You need a proper balance of omega-6s and omega-3s. Canola oil and walnut oil are highly recommended.

It's possible to boost alertness, memory and stress resistance by supplying food components that are precursors of important brain neurotransmitters. One of them is choline, the fat-like B vitamin found in eggs. Studies show that choline supplementation enhances memory and reaction time in animals, especially aging animals. It also enhances memory in people. Choline supplementation also minimizes fatigue. In one study, choline given during a 20-mile run improved running time by a significant amount..

Mood and mental performance are powerfully influenced by the B vitamins. Unfortunately, marginal deficiency in many B vitamins is widespread in North America.

Research has identified some other ways to influence mental performance:

• Sugar can make you sharp -- although no one can figure out what is the right dose at the right time.
• Carbohydrates -- especially when eaten with no protein or fat -- may indeed be mentally soothing. Muzak for the mind. There are times when we all need some of that.