"Biomarker studies of PUFA [polyunsaturated fatty acid] and treatment studies of n-3 [omega-3] PUFA in bipolar disorder show promise for indicating a way forward in the study of PUFA in bipolar disorder."
I don't want to labour any points raised by the review of studies published by Erika Saunders and colleagues  looking at fatty acids and bipolar disorder but there does seem to be a familiar ring to the current evidence base on how for at least 'some' cases of bipolar disorder, there may be something of a fatty acid element to the presentation of symptoms.
I say familiar because not so long ago on this blog I was discussing how a particular type of fatty acid - a particular omega-3 fatty acid - might show some clinical 'promise' in cases of depression (see here). Assuming that bipolar disorder - "formerly known as manic depression, is a condition that affects your moods, which can swing from one extreme to another" according to the NHS Choices entry on the condition - is not a million miles away from some of the depression cited by Hallahan et al , one might see something of a connection or two potentially uniting findings.
Saunders et al reported that their review of the current peer-reviewed literature (up to about 2015) found some support for: (a) "low n-3 red blood cell PUFA concentrations and correlations with clinical severity in studies of plasma concentrations in symptomatic bipolar disorder" and (b) "published n-3 PUFA dietary supplementation trials for bipolar disorder indicate efficacy in treatment for mania or depression." The main caveat on the last point being that depending on the trial type (open trial vs. randomised controlled trial) there were a mixture of results. One has to be quite careful.
More to do in this area? Yes there is. Lots more to do including further testing of whether fatty acid supplementation as an add-on to other more well-known interventions  may be something to consider . I assume such work would also be mindful that fatty acid supplementation may not always be something that can be mixed with more traditional pharmacotherapies.
Mechanism of effect? Unknown at present but one gets the impression that fatty acid chemistry intersecting with immune system involvement (i.e. inflammation or inflammatory processes) might be a front-runner given what has been previously discussed in this area (see here). Again, there is a research agenda to be followed.
Obviously no-one is suggesting that taking fatty acids or 'adjusting' fatty acid levels is going to be some sort of cure-all for bipolar disorder or anything else. But such results as well as adding to the increasingly important concept of nutritional psychiatry (see here) offer some further intriguing avenues when looking at such an important condition. That also includes in cases of bipolar disorder appearing alongside other diagnoses (see here) too...
 Saunders EF. et al. Omega-3 and Omega-6 Polyunsaturated Fatty Acids in Bipolar Disorder: A Review of Biomarker and Treatment Studies. J Clin Psychiatry. 2016 Sep 13.
 Hallahan B. et al. Efficacy of omega-3 highly unsaturated fatty acids in the treatment of depression. Br J Psychiatry. 2016 Sep;209(3):192-201.
 Malhi GS. & Outhred T. Therapeutic Mechanisms of Lithium in Bipolar Disorder: Recent Advances and Current Understanding. CNS Drugs. 2016 Sep 14.
 Shakeri J. et al. Effects of Omega-3 Supplement in the Treatment of Patients with Bipolar I Disorder. Int J Prev Med. 2016 May 19;7:77.
Saunders EF, Ramsden CE, Sherazy MS, Gelenberg AJ, Davis JM, & Rapoport SI (2016). Omega-3 and Omega-6 Polyunsaturated Fatty Acids in Bipolar Disorder: A Review of Biomarker and Treatment Studies. The Journal of clinical psychiatry PMID: 27631140