They occur naturally in fish, flaxseed, canola oil, nuts and avocados. They're also extracted, packaged and sold in dozens of dietary supplements. Increasingly, they even show up on grocery shelves as the latest fortification in such popular fare as bread, eggs, dairy products, margarine, baby food and cereal.
Omega-3 fatty acids are already prized by cardiologists for protecting the heart against the inflammation that can lead to blocked arteries and for thwarting an irregular, often fatal, heartbeat. There's growing evidence that these polyunsaturated fats may also be helpful in preventing complications of diabetes and in soothing the inflamed joints of arthritis.
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Now psychiatrists are also taking a closer look. Omega-3s, dubbed the "happy" fats in some quarters, are under investigation for treating depression, bipolar disease, attention-deficit hyperactivity disorder, alcoholism, Alzheimer's disease and even the so-called baby blues, or postpartum depression. Earlier this year, the American Psychiatric Association formed a committee to review the findings to make treatment recommendations for the use of omega 3s.
What makes this emerging science particularly intriguing is that the evidence for the fats' various benefits comes from several types of research: population studies, clinical trials and basic neurochemistry.
"Not only are the data consistent in those areas, but they are very robust," says Joseph R. Hibbeln, chief of the outpatient clinic at the Laboratory of Membrane Biochemistry and Biophysics at the National Institute of Alcohol Abuse and Alcoholism (NIAAA) in Bethesda.
And since there are few if any side effects to eating foods rich in omega-3 fatty acids, there's little downside to investigating these healthy fats -- and a lot to be gained. Fish, and even fish oil dietary supplements, are far cheaper than most prescription medications. Plus, there's the hope that omega-3s may help bridge the treatment gap in mental disorders -- up to 30 percent of people being treated for depression, for example, find drugs inadequate in controlling their symptoms.
"The main problem we have with depression is that we do not have treatment that [dependably] provides complete recovery," says David Kupfer, head of psychiatry at the University of Pittsburgh's Western Psychiatric Institute and Clinic. "We're still leaving people mildly depressed or unable to function well. It's like trying to make the last 10 yards when you're in field goal range. The same drug is not going to do it. It has to be some sort of adjunctive treatment. Whether that will come from omega-3s, St. John's wort or some other nutritional thing, we just don't know yet."
The idea that omega-3 fatty acids might help treat mental disorders dawned on Hibbeln in 1984 when he was standing in an anatomy lab. "I had cut open the brain, and it just very much struck me that it is mostly fat," he says. "The biochemistry of fat and lipids just seemed to be very unexplored in psychiatric disorders and that seemed odd because there are many profound neurological disorders that are known to be caused by lipid problems."
It's well recognized, for example, that multiple sclerosis damages the fatty myelin sheaths of nerve cells. Another neurological disorder, Gaucher's disease, results from the buildup of harmful fatty substances in cells, and a whole class of neurological disorders called leukodystrophies are caused by flawed development or maintenance of the fatty myelin in nerve cells.
The brain itself, is, in fact, about 60 percent fat, giving new meaning to the term fathead. But unlike other adipose tissue throughout the body, the brain's fat is diverse, "as diverse as proteins in the body," notes Hibbeln.
Essential fatty acids are fats that can't be produced by the body but are required for good health. They play key roles in the structure of brain cells and of the eye, particularly the retina. They're vital for each neuron's membrane, both its outer protection and its means of accessing key nutrients. And it is these essential fats that regulate the growth of long tendrils called axons that enable neurons to communicate with each other.
Oddly enough, while the body can manufacture saturated fat, cholesterol and even some unsaturated fat -- it is incapable of producing two of the fatty acids that are most vital. One is an omega-3 fatty acid called alpha linolenic acid, which is found in fish, canola oil and flaxseed. The other is an omega-6 fatty acid with the maddeningly similar name of linoleic acid, which is found in soybean, safflower and corn oils, as well as in meat, poultry, fish and such popular fare as processed foods. Omega-3s and omega-6s are close enough in chemical structure to be able to compete for the same molecular machinery that allows entry into the brain. (Omega-3 fatty acid molecules have three carbon atoms on one end; omega-6 fatty acids have six.)
That fact might simply still be a little quirk of nature had not a huge shift occurred in diets during the past century. In 1909, Americans got most of their fat from free-range animals, which have higher levels of omega-3s than the chicken, beef and pork commonly eaten today. They also consumed about 0.02 pounds per year of soybean oil -- a number that increased gradually until about 1960, when "soybean oil took over the U.S. food chain," says William Lands, a retired biochemist with NIAAA. "It was like a tsunami."
By 1999, soybean oil -- a major ingredient in crackers, bread, salad dressings, baked goods and processed food of all sorts -- accounted for 20 percent of total calories consumed in the United States, according to the U.S. Department of Agriculture. Per capita consumption reached 25 pounds per year. "That means that there has been an 1,000-fold increase in [consumption of] omega-6 fatty acids" over 100 years, Hibbeln says. "So we have literally changed the composition of people's bodies and their brains. A very interesting question, which we don't know the answer to yet, is to what degree the dietary change has changed overall behavior in our society."