Investigation of the Effect of Krill and Fish Oil Intake on Clinical and Biochemical Findings and Eating Behavior in Adult Individuals With Major Depression Disorders

Introduction

Major Depressive Disorder (MDD) affects approximately 6% of the adult population worldwide each year and is the second greatest contributor to the burden of chronic disease. In the treatment of MDD, both psychotherapy and psychopharmacology are effective. However, approximately 30% of patients do not achieve definitive recovery even after several treatment attempts. Major depressive disorder can affect an individual's life as a whole and is difficult to treat due to its high rate of relapse, and it is often associated with anxiety and cardiovascular diseases (CVD), which can threaten an individual's life. It is estimated that major depression is responsible for 3% of the global burden of disease according to the World Health Organization (WHO) report and that this rate may increase to 7% by 2030. Therefore, alternatives to effective treatments and prevention strategies are urgently needed due to this increasing trend.

Omega-3 polyunsaturated fatty acids (n-3 PUFAs), identified with fish oil, became one of the most researched nutritional topics on the effects of major depressive disorder. Omega-3 polyunsaturated fatty acids are shown to be effective in cardiovascular disease (CVD) prevention due to their anti-inflammatory and cardio-protective effects. It can potentially share common mechanisms with CVD, considering factors such as increased production of pro-inflammatory cytokines, endothelial dysfunction and increases in plasma homocysteine levels, which play a role in the pathophysiology of some psychiatric disorders such as depression. It is possible that omega-3 has multiple positive effects on depression through its neurogenesis and neuroplasticity abilities, as well as having a positive effect on pathophysiological mechanisms. Appleton et al. conducted a Cochrane review to investigate the effect of n-3 PUFA supplements on depression in adults. This review included 25 studies (total 1438 participants) investigating the effect of n-3 PUFA supplements versus placebo and 1 study (40 participants) comparing n-3 PUFA supplements with antidepressant treatment. As a result, it was reported that n-3 PUFA supplements had a modestly positive effect on depression compared to placebo. However, it was emphasized in this report that the majority of the studies (22 studies) had a low level of evidence. This was attributed to factors such as high levels of bias, duration of follow-up, methodological errors and deficiencies due to blinded designs. The general conclusion of the authors was that there was a need for high quality intervention studies in this field.

Although there are a large number of studies focusing on the use of fish oil in depression, research using krill oil, another source rich in n-3 PUFAs, is very limited. Krill oil is an important shellfish that lives in the oceans around the Antarctic continent and attracts attention in research due to its rich omega-3 fatty acid content. As krill is a species living in cold regions, they are rich in EPA and DHA content, along with PUFAs in the form of phospholipids and especially phosphatidylcholine in cell membrane structures. The form containing and binding Docosahexaenoic acid (DHA) and Eicosapentaenoic acid (EPA) in krill oil is phospholipids, contrary to triglyceride in fish oil. Therefore, the absorption and bioavailability activities are different because of the difference in the forms in fish and krill oil. Although there are studies on the effects of krill oil on the nervous system on the human research, there is limited research on the effectiveness of krill oil on depression. To our knowledge, there was only one pilot study on rats comparing the treatment efficacy of fish and krill oil on depression. This study compared the antidepressant effects of krill (EPA: 60 mg/500 mg, DHA: 35 mg/500 mg) and fish oil (EPA: 90 mg/500 mg, DHA: 60 mg/500 mg), vitamin B12 and imipramine. As a result, krill oil showed favorable results on a number of variables compared to fish oil, but similar results were found in both groups. It is important to compare the efficacy of krill and fish oil with similar EPA and DHA content on depression to clarify the question of which of these oils in different forms may be more effective on the disease.

Major depressive disorders affect many mechanisms such as food intake, taste perception and food selection. When clinical pictures related to the nutritional status of depressed individuals are examined; changes in appetite, increased consumption of certain food groups and related changes in body weight are frequently observed. In addition, antidepressant drugs used may also affect food intake and weight control. Eating behavior is under the control of complex neural mechanisms, especially serotonin. At the same time, food intake is also effective in the control of serotonin release in serotonergic neurons. Serotonin, which has a bidirectional relationship with eating behavior, is a neurotransmitter involved in the physiopathology of many psychiatric disorders. The presence of a disorder in the serotonin pathway may explain the development of both psychiatric disorders and obesity in the patient. As a result, it was reported that eating behavior disorders, interest in unhealthy food consumption and increased appetite in major depressives, as in some psychiatric disorders, may lead to an increase in body weight in individuals during the illness or in progressive processes. There are several studies examining the relationship between depression and obesity. However, clinical studies to determine the factors leading to this condition are limited. In addition, data collection on eating behavior, appetite and weight status is neglected in most clinical interventions in patients with depression. Therefore, it is important to investigate the efficacy of n-3 fatty acids on appetite and body composition as well as eating behaviors that examine food cravings in depressed individuals.