As noted earlier (Chapter 5), an increase in Bipolar II Disorder (BP II) is suggested. Any prevalence increase could be artefactual, reflecting changes in attribution, definition, destigmatisation, help-seeking or other factors. Alternately, there may have been a real increase and numerous determinants have been proposed, including genetic factors, greater use of illicit drugs and many social and environmental factors. In relation to the last, there has been considerable interest in a dietary contribution, particularly involving omega-3 fatty acids.
What are omega-3 fatty acids?
Omega-3 (n-3) fatty acids are long-chain polyunsaturated fatty acids (PUFAs) found in various plant and marine life. The marine-based n-3 PUFAs primarily consist of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), and appear to be highly biologically active. In contrast, plant-based n-3 PUFAs, from flaxseed, walnuts and canola oil, are usually in the form of the parent n-3 PUFA, alpha-linolenic acid (ALA). Although dietary ALA can be endogenously converted to EPA and DHA (see the metabolic pathways in Figure 11.1), this process occurs inefficiently, with only 10–15% of ALA being metabolised in this way.
The history of n-3 PUFAs
In the last 150 years, rapid expansion in western populations has been associated with a change in diet, with n-3 PUFAs from fish, wild game and plants being replaced by saturated fats from domestic animals and omega-6 (n-6) PUFAs from common vegetable oils (corn, safflower and soybean) and other sources such as wheat germ.