The World Health Organisation declared that more than 264 million people are affected by depression [1]. Over the years, research suggests the Mediterranean diet has the potential to reduce depression [2] however, the evidence is mixed. In BMC Medicine, Professor Almudena Sanchez- Villegas published a study that demonstrated the Mediterranean diet had no significant reduction in depression risk amongst adults [3].

Studies measuring the efficacy of the Mediterranean diet is challenging due to the following factors:

• • • confounding variables (alcohol, smoking, exercise) that are contributory factors to depression
    • false reports of adherence to the diet
    • the diet varies throughout the Mediterranean countries

Despite the limitations in the design of the studies, a systematic review published in the Journal of Neurology, Psychiatry and Brain Research demonstrated that 85% of studies reduced the progression of depression [5], and showed fewer side effects. The diet has also been ranked as the number 1 diet for brain health by the U.S News & World Report [4], so let’s delve into how Mediterranean diet foods could reduce risk factors associated with depression.

What causes depression?

3 prevailing theories for the cause of depression are the chemical imbalance theory, mitochondria dysfunction, and oxidative stress [6].

Chemical imbalance theory: Depression can be caused by an influx or scarcity of chemicals, such as serotonin, in the brain. Serotonin is referred to as a happy chemical due to its role in regulating mood. Pharmaceutical drugs such as Prozac and Xanax are widely used to treat depression by correcting the chemical imbalance of serotonin in the brain. A study confirmed that natural alternatives such as 5-HTP is just as effective in providing an antidepressant effect with fewer side effects [7]. 5-HTP is a building block to serotonin and has been shown to improve depressive symptoms in 67.8% of patients [8].

Mitochondria dysfunction: Mitochondria are like microscopic batteries that release energy bubbles called ATP in brain cells. Neurons require approximately 4.7 billion ATP molecules to be activated so they can release chemical messengers such as serotonin [9]. Mitochondria dysfunction can lead to the loss of connective tissue in the brain , contributing to the risk of depression [10].

Oxidative stress: oxidative stress is a consequence of elevated levels of free radicals [11]. Free radicals are reactive molecules that seek to bind their unpaired electron to another cell. Some unfortunate pairing can cause damage to the DNA in mitochondria causing mitochondrial dysfunction and damage to brain cell functions. High levels of cortisol from long terms stressors [12] and high sugar diets [13] can elicit the increased release of free radicals in the brain which can induce oxidative stress. Studies showed that depressed patients had higher levels of free radicals [14] and increased markers of inflammation and oxidative stress [15].

How does the Mediterranean diet reduce oxidative stress?

Good news is that the Mediterranean diet is rich in antioxidants, the defenders against oxidative stress. They ‘mop up’ free radicals as they are preferential binders. As a result, they reduce inflammation and protect brain cells from the damage caused by oxidative stress [16]. The antioxidant capacity of different foods can be measured by the oxygen radical absorbance capacity unit. The food you eat supplies different types of antioxidants such as vitamin C, selenium, flavonoids, and polyphenols. The Mediterranean diet is based on a higher consumption of fruit, vegetables, and fish which can provide a richer source of powerful antioxidants.

The Red wine paradox

Some forms of the Mediterranean diet recommend the consumption of one glass of red wine daily. It is a source of polyphenols which can have an antioxidant effect. The challenge with alcohol consumption is that the break brown of ethanol in the brain causes significant oxidative stress. It would be fantastic to have evidence to demonstrate the oxidative properties in red wine offset the damage done but it is difficult to validate in a clinical setting.

The brain’s response to a high intake of protein

The consumption of Mediterranean diet foods such as fish, nuts, seeds, and dairy are rich sources of proteins. Tryptophan is an amino acid and a building block to serotonin, your feel-good chemical messenger. A study found that adults that consumed a tryptophan-rich diet experienced fewer depressive symptoms compared to those that had a low tryptophan diet [17]. If you consume 100ml of skimmed milk it contains 43mg of tryptophan, 100mg of yellow fin tuna contains 313mg of tryptophan [18] and 100g of roasted cashew nuts contains 93mg of tryptophan [19].

Tyrosine is also an amino acid and a building block to dopamine, your reward and pleasure chemical messenger. A study published by Neuropsychopharmacology discovered that a tyrosine depleted diet elicited a lowering of mood amongst healthy women. If you consumed 100g of low-fat ricotta cheese can obtain 596mg of tyrosine, 100g of large white beans contain 247mg of tyrosine, [20], 100g of butternuts contain 963mg of tyrosine and 100g of hemp seed contains 1263mg of tyrosine [21] .

What are the characteristics of the Mediterranean diet?

Here you can find a hierarchy pyramid of the food groups consumed in a Mediterranean diet [22].

Here is a meal plan of Mediterranean diet recipes: ● Breakfast: a 3-ingredient mixed berry yoghurt recipe [23] offers you at least an ORAC value of 5962 antioxidants [24] and at least 63mg of tryptophan [25].

● Poached egg Caprese recipe [26] offers you at least an ORAC value of 2754 antioxidants [27] and 331.2mg of tryptophan [28].

● Lunch: A Greek salad recipe [29] offers you at least 32.25mg of tryptophan [30]and an ORAC value of 2224 antioxidants [31].

● Dinner: you might want to try a Mediterranean fish casserole recipe [32] which contains 350mg of tryptophan [33] and an ORAC value of 1758.41 antioxidants [34].