Apple founder Steve Jobs once swore that his fruit-heavy diet helped fuel his creativity and positive mood. Sceptical, the journalist interviewing him construed his remark to be a form of modesty, but science supports the late but brilliant CEO. Not only do the nutrients we consume affect our mood, but they also influence our desires and behaviour. And for a considerable period of time.
The notion that certain foods have a positive effect on mood is nothing new. As far back as the Middle Ages, people believed that different foods had specific effects on behaviour. Fruits such as quince, dates and elderberries were associated with improving mood, while lettuce, chicory and purslane were valued for their tranquillising effects (1). While it’s unlikely that this folklore wholly reflects scientific reality, it has to be said that the general principle is sound. Behind it lie at least two well-substantiated theories which are entirely compatible with each other.
One of the most convincing theories behind the mood/diet connection is the serotonin theory (2). Serotonin is an important neurotransmitter produced in the brain, synthesis of which depends on the availability of tryptophan. It plays a role in controlling sleep, appetite, impulsiveness and in particular, mood: scientists have shown that high circulating levels of serotonin correlate with improvements in mood. Logic would therefore suggest that to improve mood, we should prioritise serotonin-containing foods in our diet such as bananas, and foods rich in tryptophan (the serotonin precursor) such as chicken and eggs. But the logic is wrong. And it’s often erroneously propagated by the authors of poorly-researched articles in the general press and certain health blogs. In reality, it is completely unrealistic to rely on dietary sources of serotonin for this purpose inasmuch as it cannot cross the blood-brain barrier. Neither can you hope to boost your serotonin levels by eating copious amounts of tryptophan-rich foods: it’s not the amount of tryptophan that’s the issue here but the ratio between tryptophan and the other amino acids. To clarify, eating chicken will certainly increase your intake of tryptophan, but it will also increase that of all the other amino acids. This results in fierce competition between these amino acids for use of the body’s transporters. Specific to amino acids, these transporters are very important: they provide access to the body’s various tissues. Without them, tryptophan cannot cross the blood-brain barrier and is thus unable to influence serotonin synthesis.
The problem is that of all the amino acids, tryptophan is probably the least abundant in animal protein sources. While such foods may contain a reasonable amount of tryptophan, they will contain even higher levels of leucine, lysine, methionine and threonine. In competition with all these other amino acids, tryptophan therefore struggles to get access to the transporters. This is why a protein-rich diet decreases the availability of tryptophan to the brain and actually ends up reducing serotonin synthesis.
To get round this problem, it’s advisable to choose dietary sources that contain a reasonable amount of tryptophan but which are low in amino acids in general (3). And such foods are readily available: they’re the foods that most hunter-gatherers used to eat throughout the day: fruits and vegetables. Thus the entrepreneur Steve Jobs was absolutely right: there is indeed a correlation between consumption of fruit and vegetables and mood (4-9). Fruits – and even more so, vegetables – contain complex carbohydrates which gradually raise blood sugar levels. This sharp influx of carbohydrates triggers the release of the well-known hormone insulin, which in turn, encourages muscle tissues to take up the amino acids circulating in the blood vessels. But they make an exception with tryptophan which, with its competitors ‘out of the frame’, is free to bind to the transporters.
This well-substantiated theory is consistent with the observations of scientists and the results of clinical trials conducted over recent years. Researchers have noted that eating large amounts of foods high in complex carbohydrates and low in protein helps improve mood, particularly in people suffering from chronic stress, seasonal blues, low mood, and obvious depression. In a study of young adults in New Zealand, researchers found that a diet high in fruit and vegetables made the participants calmer, happier and in better shape in their daily life (10). The study lasted 21 days: each evening, the subjects were asked to record their state of mind in a journal with the aid of a grid of positive and negative adjectives. The researchers then identified relationships between the participants’ mood and the foods they had eaten during the day. How did they know whether the subjects had eaten fruits and vegetables because they felt happy or whether eating those foods had made them happy? In other words, which came first? To be certain, the scientists cross-referenced the data and found that the volunteers’ mood tended to improve the day after they had eaten meals high in fruit and vegetables. The foods had therefore caused the improvement in their mood and had triggered a virtuous circle.
Note: it’s important not to confuse complex carbohydrates with simple carbohydrates! Foods high in simple carbs such as refined cereals, white rice, sweet biscuits or fruit juices, trigger a sudden glycaemic response which is always accompanied by a spike in adrenaline (11), known as the ‘stress hormone’. In the long term, eating such foods leads to a worse response to stress and a deterioration in mood.
The best tryptophan-rich fruits and vegetables to eat in order to improve your mood are:
Other tips to stimulate serotonin production:
The second theory is based on the role played by omega-3 fatty acids in the body: this is the anti-inflammatory theory. It’s well-established that these valuable fatty acids are able to prevent cardiovascular disease due to their anti-inflammatory properties (12). What is less well-known is that they also have a beneficial effect on mental health (13-15). Researchers have demonstrated a link between low levels of omega-3 fatty acids and mood disorders, including depression and risk of suicide (16-18).
Some years ago, scientists studying the positive effects of omega-3 in lowering cardiovascular risk noticed that participants also benefited from elevated mood. Researchers later realised that mood problems and cardiovascular diseases shared certain pathophysiological mechanisms, in particular, abnormally high production of pro-inflammatory cytokines and critical homocysteine plasma levels (19). But there are other explanations for these observations. We also know that omega-3 fatty acids, including ALA, EPA and DHA, play an active role in the structure of brain cell membranes. When intake of these fatty acids is too low (which is most of the time nowadays), we see changes in brain development, impaired composition of nerve endings, and physiological, neurosensory and behavioural irregularities. Studies on experimental models have shown that a lack of omega-3 leads to cognitive deficiencies, particularly learning (20-22), and abnormal metabolism of certain neurotransmitters involved in mood (23-24) (especially melatonin). These deficiencies can be corrected through diet or appropriate supplementation (25).
A number of studies support this hypothesis. In a cohort of 4644 New Zealand subjects aged 15+, personal perception of improved mental and physical state was found to be proportional to consumption of fish, and thus omega-3 fatty acids, which are therefore considered to be mood-stabilisers (26). Research also shows omega-3 concentrations in red blood cell membranes to be low in depressed individuals, while other studies confirm the efficacy of DHA for mild depression (27), post-partum depression (28), and winter depression (29), with measurable morphological changes (30) (decreased volume of lateral ventricles).
According to one Australian study author (31), it is therefore possible to improve your mood by regularly including omega-3 fatty acids in your diet, particularly at breakfast.
Plant sources (1.5g ALA) :
Marine sources (1.5g of EPA + DHA):
As eating more than two portions of oily fish a week is not recommended, omega-3 supplements (natural-source EPA and DHA) offer a useful alternative for obtaining a regular amount of omega-3 every day.
Note: make sure you reduce your intake of omega-6 if you’re consuming omega-3. In excess, omega 6 fatty acids can counteract the beneficial effects of omega-3 by monopolising the enzymes required for their metabolism. The richest sources of omega-6 are primarily processed foods and certain oils (safflower oil, grapeseed oil, sesame oil, sunflower oil and corn oil).
Omega-3 and tryptophan are excellent options for rapidly and durably improving your mood. But scientists have also discovered additional – and complementary – ways of doing this.
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