Research is increasingly demonstrating that there is a relationship between our mood and the food we consume, which is the theme we are going to explore today, specifically looking at factors affecting our gut-brain axis (1).
Our gut microbiome communicates to our brain via the gut-brain axis, so it can exert an influence over immune and hormone signalling in our brain. Preliminary evidence in humans suggests that our gut microbiome is altered in depression. So, what can we do to support our gut microbiome? (2,3)
Mediterranean Dietary Pattern
Following a Mediterranean dietary pattern has been associated with better mental health (4). The Mediterranean diet is based on (5,6):
- A high daily intake of plant foods, including fruits and vegetables, wholegrain, legumes and nuts.
- Abundant use of extra virgin olive oil.
- A moderate intake of fish, white meats, yoghurt, cheese, and eggs.
- Low consumption of red and processed meat and sweets.
One study investigated the effect of the Mediterranean diet in 67 individuals diagnosed with Major Depressive Disorder and found remission in 32.2% in the Mediterranean diet group compared to 8% in the control group. It must be noted that this was a small sample, of whom 72% were female, so it cannot be generalised to the wider population; however, it does indicate that a Mediterranean dietary pattern may be beneficial for our mental health (7), and the results have been supported in other studies. So, let’s unpack some of the elements of the Mediterranean diet.
Oily fish is a good source of our essential fatty acids, like omega-3 and omega-6. Our central nervous system, which consists of our brain and spinal cord, has the second-highest concentration of lipids in our body, behind adipose tissue. Of these lipids, the brain has particularly high concentrations of omega-3 and omega-6. Research has associated low dietary omega-3 and a high omega-6 to omega-3 ratio with anxiety and depression (9). It is recommended to include one to two portions of oily fish a week, such as anchovies and salmon. If not eating fish for any reason, it may be worth talking with a registered nutritionist or dietitian and considering an algae supplement (10).
Fibre is also an important feature of the Mediterranean diet and may influence our mood by promoting beneficial bacteria in our gut microbiome, producing anti-inflammatory metabolites. These metabolites enter our bloodstream and have widespread positive effects on our health, including our mental health (11,12). Consuming a diet diverse in plant foods can help to increase our fibre intake.
Probiotics are live bacteria that, when consumed in adequate amounts, may have beneficial effects on our health (13). Preliminary research giving healthy women a fermented milk product with probiotics for four weeks found that it affected the activity of brain regions important in the processing of emotion and sensation (14). Further research found that long term administration of Lactobacilli and Bifidobacteria, strains of bacteria often found in probiotics, can have similar effects to anti-depressants on areas in our brains related to emotion and mood (15). Probiotics are not regulated, so the concentration and specific strains found in probiotics products may vary. This means labelling cannot claim that probiotics have health benefits, and further research is needed to look at this relationship (16). If thinking about taking a probiotic, talk with a registered nutritionist or dietitian.
Research finds that stress can change the composition of our gut microbiome, increasing pro-inflammatory substances (17). Therefore, trying to reduce stress may help our gut microbiome and mood. Research indicates that intuitive eating, eating based on recognising our physiological hunger and satiety cues, predicts better long-term psychology and behavioural health (18). More information about where to start with intuitive eating can be found in this article by Sophie here.
The Glycaemic Index (GI) is a rating system used for carbohydrates to show how quickly the food affects our blood sugar level when eaten on its own. High GI foods include sugar-sweetened beverages, white bread, and potatoes. Low and medium GI foods include pulses, wholegrain and some fruits and vegetables (19). It must be highlighted that the clinical significance of the GI remains the subject of debate (20).
Research has proposed that there is a relationship between the glycaemic index of food and mood. Much of the research in this area is in diabetic patients, which finds a positive association between high GI diets and depression. This research is only a correlation, so we cannot say high GI diets are causing depression, only that there is an association (21,22). However, research in different populations has found similar suggesting that high GI diets may be a risk factor for depression in postmenopausal women (23).
Importantly, this does not mean the advice is never to eat high GI foods. All foods we enjoy can have a place in our diets, and it is important to find a sustainable balance for us.
Despite research remaining in its infancy, a positive relationship between water and our mood has been suggested. This is particularly apparent in those most vulnerable to poor fluid regulation, the elderly and children (24). In contrast, when dehydration occurs, so that body mass is reduced by more than 2% (up to 60% of a human adult is water), it negatively affects our mood, increases fatigue, and decreases alertness (25). It is recommended that we drink 6 to 8 glasses of fluid a day, including plenty of water but low-fat milk, sugar-free drinks, tea and coffee all count (26)! Personally, I find always having a water bottle with me helps me make sure I drink throughout the day.
Caffeinated drinks do count towards our fluid intake and are part of a balanced diet; however, it is important to be aware that they are a stimulant. As such, small amounts can increase our awareness, mood, and perception of fatigue; however, they can increase the risk of anxiety and sleep disturbance in excess amounts. One review found 41 human studies, low to moderate caffeine intakes, between 37.5 to 450mg per day, the majority reported benefits (27).
It must be recognised that the response to caffeine varies greatly between people, and many factors affect the caffeine content of products. Health organisations generally suggest that it is safe to consume up to 300mg per day. The average cup of tea contains 11mg, and coffee contains 90mg, depending on how it is made. Green tea, chocolate and even decaffeinated coffee all also contain varying amounts of caffeine (27,28,29)!
The NHS recommend that pregnant women consume no more than 200mg, or 2 cups, of caffeinated coffee a day. This is a safe limit set as more than 600mg per day during pregnancy has been linked to insomnia, irritability, nervousness, upset stomachs and increase blood pressure (27,28,29).
- British Dietetics Association. Food and mood: Food Fact Sheet (30).
- National Health Service. What is a Mediterranean Diet? (31)
- Mind. Food and Mood (32).
Overall, the relationship between food, mood and mental health is complex, with many factors to consider. A diet that provides us with adequate amounts of all the nutrients and which we feel good eating, satisfying our personal dietary preferences, is likely to support a good mood. More research is needed to understand the mechanisms that link food and mental well-being and determine how nutrition can support our mental health (1).
Please contact a registered nutritionist or dietitian for further support if you need it.
Contribution by Emilia Fish, ANutr