Modern diet may be causing depression
26/05/2005 - Scientists have long suspected that a lack of omega-3 may contribute to depression, but the latest study suggests that an excess of omega-6 ? the fatty acid which is more prevalent in the modern diets ? may have more to do with it, reports Jess Halliday.
Omega-3 has captured the attention of food formulators, media and health-conscious consumers thanks to a huge body of scientific evidence pointing to its benefits for heart health, joint health and cognitive function.
Natural sources of omega-3 include oily fish, canola and flaxseed oils, soybeans and nuts. But while these foods were more commonly eaten 50 years ago, these days consumers' palates tend to favor foods that contain higher levels of omega-6, such as meat, eggs, poultry, cereals, breads, baked goods, vegetable oils, and margarine.
Previous studies into fatty acids and depression have measuring omega-3 levels in the blood of depressed humans, giving rise to the ?reg;phospholipid hypothesis' which proposes that decreased omega-3 fatty acid intake, and hence decreased brain omega-3 fatty acid content, could be responsible for the disease.
Because of the high dietary variability of humans and the obvious inability to study their brains, Dr Pnina Green of Tel Aviv University and Dr Gal Yadid of Bar-Ilan University chose to test the theory by comparing the brains of normal and depressed rats.
Their findings, published in the June issue of the Journal of Lipid Research, took fatty-acid research surprising direction.
The two groups of rats were fed the same diet, but their brains showed marked differences in levels of omega-6 fatty acid levels. All regions of the depressed rats' brains studied had significantly higher concentrations of arachidonic acid (ARA), a long-chain unsaturated metabolite of omega-6 fatty acid.
"The finding that in the depressive rats the omega-3 fatty acid levels were not decreased, but ARA was substantially increased as compared to controls is somewhat unexpected," said Dr Green.
"The finding lends itself nicely to the theory that increased omega-3 fatty acid intake may shift the balance between the two fatty acid families in the brain, since it has been demonstrated in animal studies that increased omega-3 fatty acid intake may result in decreased brain arachidonic acid."
But Green does not advocate cutting ARA out of the diet completely, since it is essential for the proper functioning of almost organ in the body, including the brain. It is a structural element in phospholipids, a substrate for a host of derivatives involved in second messenger function and is involved in signal transduction.
Rather she suggests that, in the future, depression may be controlled by shifting the balance between the two fatty acids ? cutting back on omega-6 and increasing intake of omega-3 to bring levels back in line with those of our forebears.
Dietary supplements are a perennial favorite for consumers wishing to boost their omega-3 intake, and eggs produced by chickens fed an omega-3 rich diet have been available for some time. But formulators are getting ever more adventurous, with new fortified products arriving on supermarket shelves almost on a weekly basis.
New entrants include bread products containing Ocean Nutrition Canada's Meg-3 ingredient from The Baker and Arnold Foods Company. Cereal companies are also tipped to be getting in on the act. In February Martek Biosciences signed a non-exclusive agreement with Kellogg to supply omega-3 for future fortified food products.
According to the Depression and Bipolar Support Alliance, depression is the most common serious brain disease in the United States, affecting more than 23 million adults each year.
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