Prozac of the sea

( Psychology Today ) Potera, Carol; 05-15-1996

It's the one nagging drawback to the low-cholesterol bandwagon (besides having to give up cheese omelets, of course). For all the benefits that cutting cholesterol bestows on the heart, researchers have linked such diets to higher rates of depression and suicide.

A few studies, though, find no connection between cholesterol and mood. And the explanation may lie in the type of polyunsaturated fat we eat, rather than cholesterol itself.

"When your doctor tells you to lower cholesterol, you usually lower your fat intake," observes Joseph Hibbeln, M.D., a psychiatrist at the National Institute of Alcohol Abuse and Alcoholism. Trouble is, a low-fat diet can deprive us of some fats, called essential fatty acids, that are required to keep our nervous and immune systems healthy. One of these is docosahexaenoic acid (DHA), an important component of brain cell membranes.

While our bodies can synthesize most fats, we must obtain essential fatty acids like DHA from food. Fish is an especially rich source of DHA, a type omega-3 polyunsaturated fat.

But it's not simply the amount of omega-3 in our diet that matters to our brains, Hibbeln suggests in the American Journal of Clinical Nutrition (Vol, 62, No. 1). What may be important for good mental health is the amount of omega-3 relative to a related fat, omega-6, that is found in corn and soybean oil. Too much omega-6 in our bodies, in tandem with too little omega-3, could increase our risk of depression. If that's the case, cholesterol may merely be an innocent bystander.

It would also mean that eating omega-3-laden fish and curbing our intake of omega 6 sources 6 might actually help protect us from depression and suicide. Indeed, in countries where folks eat lots of fish, like Taiwan and Japan, the depression rate runs 10 times lower than in North America. And when cholesterol and fat were lowered in one study by replacing animal fat with fish, depression improved rather than worsened. But in most cholesterol studies, people replace animal fats with corn oil, which the body cannot convert to DHA.

Hibbeln stresses he's not advocating that anyone change their diet just yet. But a rapidly growing body of research suggests that for cardiovascular health, not all polyunsaturated fats are created equal. It might be wise to balance the amount of each variety we eat, just as we juggle the overall proportions of fats, carbohydrates, and protein in our diet. "These issues are important to the heart," says Hibbeln, "and they're probably also important to the mind."