Fat and mood

The evolution in scientific thinking about dietary fat has changed dramatically over the past century. Once considered the primary nutritional evil, today, many praise fat as a dietary saviour that we mustn’t restrict.

But, as with most things, the truth lies somewhere in the middle. While it would be beneficial to increase the consumption of some fats, specifically monounsaturated and polyunsaturated fatty acids, there is still quality evidence to support the reduced consumption of other fats, specifically saturated and trans fatty acids.

When considering the relationship between fat and mood disorders, most of the research focuses on polyunsaturated fatty acids, which are emerging as potentially influential in both the pathogenesis and management of these conditions. Yet, current recommendations are not as straightforward as simply recommending patients to increase their intake of polyunsaturated fatty acids.

Polyunsaturated fatty acids and the brain

Polyunsaturated fatty acids (PUFA) provide a crucial structural component of all cell membranes. These fatty acids possess two or more double bonds that structurally provide them with kinks, allowing them to take up more space in the membrane, increasing fluidity and functionality. In addition, they play important physiological roles as signalling mediators. These characteristics of PUFA make them highly desirable in the brain where efficient signalling between neurons is crucial.

The human body is capable of synthesising all the fatty acids it requires with the exception of linoleic acid (LA), an omega-6 fatty acid, and alpha-linolenic acid (ALA), an omega-3 fatty acid, of which both must be consumed through diet. Despite being essential, both LA and ALA have a relatively low concentration in the brain, instead their key role is as precursors. Most notably, LA is the precursor for omega-6 arachidonic acid (ARA); and ALA is the precursor for omega-3 eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).

Omega-3 PUFA

DHA is the most researched omega-3 PUFA, perhaps because it takes up the highest concentration in the brain’s grey matter.2 It is well known to play an essential role in pre-and-postnatal brain growth, specifically the development of monoaminergic systems, such as serotonergic, dopaminergic and noradrenergic pathways.3 DHA’s involvement in the regulation of these emotional processes has researchers proposing that insufficient levels may be an important underlying mechanism that may lead to depression and other mood disorders.4 While this theory is yet to be proven, a number of studies have examined the potential role of altered brain DHA status and mood, discovering that patients experiencing the symptoms of depression almost always have lower serum concentrations of DHA.

On the other hand, EPA only represents 1–2% of total brain fatty acids, and rather than providing structural importance, it is most notable as a precursor for eicosanoids. Despite being less researched overall, current studies indicate that EPA may be more influential in mood disorders and depression. The eicosanoids derived from EPA possess anti-inflammatory properties which can indirectly benefit the brain by lowering inflammation.

Omega-6 PUFA

The omega-6 ARA is also greatly esterified to the phospholipid cell membranes in the brain, yet, similar to EPA, it also acts as a precursor for eicosanoids. Although the eicosanoids derivatives of ARA possess pro-inflammatory functions, which are certainly necessary for an effective immune system, in excess they can lead to aggravated inflammatory conditions in the brain.

Omega-6 and Omega-3 ratio

Since ALA and LA compete for the same desaturases and elongases in the synthesis of eicosanoids, a higher intake of either one will result in the increased production of the associated-inflammatory eicosanoids. Unfortunately, as a result of LA being the most abundant in nature and the most prominent in new-age Western diets, there tends to be an excess of omega-6 eicosanoid derivatives and a shortage of omega-3, encouraging an inflammatory state.10 In fact, the current Western diet encourages a ratio of omega-6 to omega-3 fatty acids of 15–20:1, which contrasts sharply with the ideal ratio of around 2:1 recommended by a panel of lipid experts.

Inflammation and mood

Mood disorders are complex and are often highly individualised. To date, researchers understand that mood disorders originate in the brain and can be associated with several potential factors, one of which is inflammation. There is an abundance of literature demonstrating increased mean concentrations of a variety of inflammatory markers in depressed patients compared with controls. While the specific effect that inflammation has on the brain is not completely understood, much of the available research indicates that inflammation can negatively influence brain plasticity and provoke changes in neural circuits, giving rise to behavioural problems that are commonly associated with mood disorders and depression. Based on what we know about the relationship between PUFAs and inflammation, researchers have hypothesised that these particular fatty acids might be involved in the pathogenesis of mood disorders and depression. In the last decade, a growing number of reports on PUFA and depression have been added to the literature, providing evidence that these fatty acids are closely linked to mental health. A significant number of studies have observed that the patients who experience symptoms of depression possess a low concentration of omega-3 fatty acids and a considerably higher concentration of omega-6 fatty acids.

Dietary recommendations

Although both omega-3 and omega-6 PUFA are essential for brain development and functionality, the current imbalance indicates that the amount of dietary omega-6 should be reduced while the amount of omega-3 should be increased.

#1 ENJOY FISH TWICE A WEEK

EPA and DHA come from fatty fish such as salmon, herring, sardines, tuna, trout and mackerel. Although neither are considered essential, their conversion from their parent precursor ALA is limited and therefore it is recommended that direct sources of EPA and DHA are also included in the diet.

#2 CONSUME QUALITY ALA-RICH PLANTS DAILY

In most cases omega-6 LA is more abundant in foods than omega-3 ALA, with the exception of canola oil, flaxseeds and walnuts. As such, these foods should be consumed in greater quantities than omega-6 LA refined vegetable oils and the processed foods that contain them.

#3 CHOOSE GRASS-FED MEAT

In the process of mass-producing meat, the composition of the animal diet has changed, with grain now favoured as an easier and more effective (in terms of faster growth) food source. However, cattle that have been fed grain have their fatty acid ratio in favour of omega-6. Alternatively, grass-fed beef tends to have a lower omega-6 to omega-3 ratio, closer to 2:1.

Supplementation recommendations

While healthy individuals who eat fatty fish at least twice a week should obtain adequate dietary omega-3, many individuals struggle to meet this expectation. In these cases, an omega-3 (fish oil) supplement should be considered. Current guidelines recommend a target dose of around 1 g of EPA plus DHA per day, which would correspond to eating three salmon meals per week.

For patients who have allergies or choose not to consume fish-based products for ethical reasons, algal oil derived from algae may be a good source of EPA and DHA; however, studies have not been extensive.

For mood disorders, manipulating dietary intake of omega-3 and omega-6 has not, so far, proved significant as a monotherapy. However, mounting evidence suggests that a favourable ratio between the two PUFA holds great promise in the management of mood disorders. As such, health professionals should consider recommending dietary intervention, but only as a complementary treatment alongside pharmacological and psychological therapies.