How to Eat Smart

Other investigators have also observed a positive correlation between triglyceride values, hostile acts, and a domineering attitude. In addition, lowering triglyceride levels improves scores on dementia screening tests in elderly patients. What more, regimens such as the Pritikin diet, aimed at lowering triglycerides and cholesterol, also reduce depression and hostility, suggesting that cholesterol-lowering medications are not the mood-altering factor.

Obviously, not all psychological or psychiatric disorders are attributable to triglycerides and saturated fats, notes Glueck. Nevertheless, his research suggests that high blood-fat levels can be the sole cause of depression in some cases, and that they may exacerbate mental problems due to other causes. Consequently, Glueck recommends that anyone with a psychiatric problem or who is suffering from depression should have his or her cholesterol and triglyceride levels tested.

Fats and Smarts

A diet high in saturated fat not only can make you depressed and downright antisocial, it can also impair general mental performance. So will a diet high in total fat and one that is deficient in essential fatty acids (EFAs).

Once dietary fats are broken down into fatty acids, the body uses them for myriad purposes. They go into all hormones. They are critical to body metabolism. And they are also a constituent of the outer membrane of every cell in the body, including those in the brain. Of the numerous fatty acids the body uses, two are called "essential" because they cannot be manufactured in the body; they must be supplied by daily diet. These are linoleic acid, or n-6, and linolenic acid, or n-3; both are super-unsaturated fats. (You need only about a tablespoon of EFAs daily.)

N-3 fatty acids—popularly called omega-3s—are known to be particularly crucial for proper development of the human brain, both before birth and in infancy it is through the lipid-rich cell membrane of neurons that all nerve signals must pass. In addition, as learning and memory forge new connections between nerve cells, new membranes are formed to sheath them. All brain cell membranes continuously need to refresh themselves with a new supply of fatty acids. Preliminary research suggests that EFAs—particularly n-3s—are best suited for optimal brain function.

In a key animal study, Carol E. Greenwood, Ph.D., and colleagues fed rats various amounts and types of fat for a three-month period and then measured their performance on memory tests. Fat content ranged from 40 percent of calories—approximating that of the average American—to 10 percent of calories. Rats fed the high-fat diet that was highest in saturated fat (from lard) performed the worst. Those on the diet lowest in saturated and total fat did the best.

While consuming too much saturated fat and too much fat overall, many North Americans may not be consuming anywhere near enough n-3 fatty acids for optimum brain health, notes Greenwood, associate professor of nutritional sciences at the University of Toronto. The polyunsaturated vegetable oils touted as healthful for the heart and so widely used in cooking and in prepared foods—corn, safflower, and sunflower oils—have almost no n-3s. Instead they are loaded with n-6s. Unless balanced with a large amount of n-3s, n-6s are associated with abnormalities of immune function, inflammation, and even cancer. Greenwood suggests using canola (rapeseed), soy, and walnut oils, which have ample n-3s in a healthful ratio to n-6s.

In a study at Oregon Health Sciences University, a team led by William Connor, M.D., fed infant rhesus monkeys a diet containing adequate amounts of fat but the fat was supplied in one of two forms—soybean oil, rich in n-3s, or safflower oil, deficient in n-3s. The EFA-deficient monkeys grew well, but their visual development was impaired; acuity was 50 percent of normal. In addition, notes Connor, professor of medicine, the n-3-deprived infants "seemed to pace back and forth purposelessly," suggesting a neurological defect. Autopsy showed numerous abnormalities in brain neurons, Connor reports.

So the old saw about fish being brain food is true; they are rich in n-3s. Long a proponent of adding more n-3-rich fatty fish to the diet as a way to reduce the risk of heart disease, Connor contends that the special n-3s in fish oil are tailor-made for the brain. Chemically speaking, they are long-chain fatty acids, containing strings of 20 or 22 carbon atoms. One such long-chain n-3 fatty acid, docosahexaenoic acid, is identical to that found in abundance in neuron membranes.

Plants also contain n-3 fatty acids, but their n-3s are arrayed in medium-length chains. Better, Connor says, to deliver to the brain—especially during development—precisely the type of fatty acid it needs and readily absorbs. In a study of infant rats, their growing brains sopped up four times more long-chain n-3s than other EFAs.