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New Evidence for Omega-6's Role in Depression
Depression has long thought to be associated with diet. In recent years many researchers have focused on what they believe is a crucial factor in depression: fatty acids. A theory, called the phospholipid hypothesis, postulates that a specific type of phospholipid, omega-3, is an important component in the physiology behind depression. However, new evidence from a study conducted in Israel challenges the theory's exclusive emphasis on omega-3.
Simply put, the phospholipid hypothesis holds that decreased omega-3 fatty acid intake could be responsible for depression. Omega-3 fatty acid concentration in the blood of depressed patients has been documented to be lower than that of non-depressed patients. Omega-3 fatty acids themselves are polyunsaturated fatty acids found in certain fish tissues and in vegetable sources such as flax seeds. So far evidence for the phospholid hypothesis has only been indirect, largely due to the variability of diet between patients and the inability to examine human brain tissue in an experimental setting. Fortunately, a recently engineered breed of rats, called the Flinders Sensitive Line (FSL), has been designed specifically to suffer from depression. This breed of rat promises to overcome obstacles associated with human experimentation.
In the Journal of Lipid Research study, Dr. Green, et al. used this new breed of rat to investigate the link between omega-3 fatty acids and depression. Samples from four regions of both the brains of FSL and control subjects were taken. After extracting lipids from these samples, a gas chromatography was run. Contrary to the phospholipid hypothesis, the researchers found that the main difference between the two types of rats was in omega-6 fatty acid levels rather than omega-3 fatty acid levels. Arachidonic acid, a long-chain unsaturated metabolite of omega-6 fatty acid, was found in higher concentrations in the FSL rats. This particular form of omega-6 serves a variety of purposes, including being involved in signal transduction and acting as a component in second messenger functions.
This finding was somewhat unexpected, but makes perfect sense when applied to another theory on the table. The other theory postulates that increased omega-3 fatty acid intake may simply shift the balance between the two fatty acid families in the brain and indirectly inhibit depression. In fact, previous research has demonstrated in animal studies that increased omega-3 fatty acid intake may actually result in decreased brain arachidonic acid Ð thus corroborating the theory and the unexpected finding. As for sources of omega-6, be sure to check out cereals, eggs, poultry, most vegetable oils, whole-grain breads, baked goods, and margarine. But as added note, several nutritionists argue omega-6s and omega-3s will produce positive effects (e.g. non-depression) when both are consumed in balanced amounts.
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