There is evidence that there is currently an epidemic of depressive and anxiety disorders in the Western nations. Some have argued this is due to improvements in diagnosis and reporting of mood disorders, but empirical evidence argues against this case and suggests the increase is real. There are many reasons why the rates of mood disorders may be increasing, but perhaps one of the main factors is an increase in stress levels in combination with a poor diet. Chronic stress is highly disruptive to neurochemistry because it causes an increase in inflammation, which in turn causes an increase in oxidative stress. The increase in oxidative stress then causes deleterious changes to the tissues of the brain, altering neuronal signalling and neurotransmitter metabolism. A high quality diet can counteract the deleterious effects of stress because high quality diets can reduce inflammation and reduce oxidative stress. This antioxidant and anti-inflammatory effect of high quality plant based diets may be why they are able to elevate mood.
One of the ways that high quality diets can reduce inflammation and oxidative stress is through the provisions of a balanced ratio of omega 3 to omega 6 fatty acids. The typical Western diet tends to contain too much omega 6 fat and not enough omega 3 fat. It has been suggested by a number of studies that Western diets high in omega 6 containing vegetable oils are a possible driver of the high rates of depression. The high levels of vegetable fat can increase levels of proinflammatory eicosanoids, and this in turn is associated with depression. Increasing the supply of omega 3 fat can redress the imbalance and may have beneficial mood elevating effects through reductions in inflammation. Studies have investigated the effects of omega 3 fatty acids on mood disorders, and the general consensus on the numerous studies that have been performed to date suggest that consumption of omega 3 fatty acids are associated with health benefits that relate to improvements in psychiatric disorders including depressed mood and anxiety.
Seasonal affective disorder is a form of depression that is more prevalent in the winter months when light levels and solar radiation are much lower. Seasonal affective disorder is associated with omega 3 consumption. It has been reported that fish consumption is inversely associated with seasonally affected disorder in a number of studies. Seasonally affected disorder is for example low in Iceland where fish consumption is high. Also, Japan has a low rate of seasonally affected disorder and the Japanese also consume high amounts of fish. In countries that consume low amounts of fish, seasonally affected disorder is much higher, despite some of these countries receiving much higher levels of sunlight. As the diets of polar communities change from a traditional high fish diet to a lower fish Western style diet, rates of seasonal affective disorder, depression, anxiety and suicide rise. Rates of depressive symptoms are much higher in individuals who consume fish infrequently compared to frequently.
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