In part 1 of our microbiota and mood series, we looked at the ways our microbiota - the collection of microorganisms living in our digestive tract, including bacteria, fungi and viruses - affect our mood, and can influence our risk of anxiety and depression.

In part 2, we’re going to look at the key dietary principles that can support our mental well-being, specifically because they feed and nourish beneficial gut bacteria. When we feed up our beneficial microbiota, we encourage a diverse and flourishing inner ecosystem that reduces inflammation, encourages butyrate production and supports mood.

The great thing about modifying your microbiota to improve mental well-being is that the first steps can be all about ADDING things to your diet, rather than removing them. This is a “microbiota-first” approach and is often more positively received by anyone new to diet and lifestyle change.

Important to note that there are lifestyle practices other than diet that can improve microbiota composition - like exercise and reducing stress. Check out this article in our library for an overview of “mind-down” approaches to improve gut health - such as mindfulness and ACT (Acceptance & Commitment Therapy) techniques.

1. Diversity is the spice of life

In general, a diverse microbiota is a healthy microbiota.

If you know anything about finance, you’ll know that diversifying your investments across a wide variety of industries or classes is one of the best strategies for reducing risk.

The same applies to your microbiota - the more diverse it is, the more resilient it is, and the more likely that you’ll reap the benefits of long-term health and well-being.

Science shows there is a connection between a lack of microbiota diversity and disease, including allergies and asthma, obesity, diabetes, and body-wide inflammation.

The people and populations who eat the widest variety and diversity of whole-plant foods have greater microbial diversity scores than others. The reason is that fibre is not just one thing - it's made up of hundreds of different forms, shapes and sizes. Some microbes will eat all types and others will be very specific about the fibre they prefer to consume - similar to a fussy child! Unless you are consuming their preferred food source, microbes can reduce in numbers or even die out, reducing overall diversity.

Here are our top clinical tips for maintaining a diverse ecosystem:

Eat a minimum of 40 different, whole, minimally processed plant foods each week:

• Start by doing a count of all the different types of fruits, vegetables, nuts, seeds, legumes, herbs and spices you consume in a week.

• For herbs and spices, you need to have at least a couple of tablespoons across the week to be included in the count.

• Black rice, red rice, and brown rice are counted as different foods - they contain different mixtures of fibre and polyphenols. Same for red apples versus green apples etc.

→ If you’re below 40, start to include some new plant foods - and be sure to vary the colours too.

• Eat some of these fruits, vegetables, nuts and seeds raw, as you’ll get the microbes on them adding diversity as they pass through.

• Note that fermented foods and probiotic supplements only temporarily improve diversity - they’ll have an action whilst they’re being consumed but the action won’t be permanent long-term. So whilst they’re great to include in your diet, diversification of your diet is the priority, since many of us in modern society habitually buy the same foods each week.

2. Eat plenty of prebiotic-rich foods

Once you begin the diversification process, it's useful to know what types of foods are going to give you bang for buck, in terms of microbiota nourishment and improvement in mental well-being.

Prebiotics are selectively fermented substances that encourage the growth of beneficial gut species and improve your health. Blackcurrants, for example, are particularly good for feeding up our Lactobacilli species.

A prebiotic-rich diet was found to improve mood, anxiety, stress and sleep in people whose regular diet had been low in prebiotics.

Here’s a list of foods particularly high in prebiotics:

• A variety of vegetables - asparagus, beetroot, broccoli, cabbage, fennel, globe and Jerusalem artichokes, kale, kohlrabi and parsnips

• Garlic, onions, leeks and shallots

• Plants typically used as herbs like burdock, chicory and dandelion

• Fruits like bananas, berries, cherries and blackcurrants

• Legumes e.g. red and green lentils; beans (kidney, lima, borlotti and haricot); peas and chickpeas, falafel

• Grains like oats, sourdough rye and wheat (if gluten tolerated)

Supplemental prebiotic fibres and sugars that nourish beneficial bacteria include partially hydrolysed guar gum (PHGG), FOS, Acacia fibre, Inulin, GOS and Lactulose (more commonly known as a laxative - it's used in much lower doses for microbiota modification). A combination of a couple tends to work better than just one.

The main side effect of increasing prebiotic food and supplements is bloating and distension, so these are best introduced slowly. If you have existing gut issues, see an experienced clinician for help.

3. Power up on polyphenols

Polyphenols are compounds found in brightly coloured fruits and vegetables that reach the colon intact where they feed the microbiota. The microbiota then also convert them into compounds that are helpful for our health.

Here are some polyphenol-rich foods:

• Fruits: Cherries, strawberries, blackberries, plums, raspberries, red apples, black grapes, Black olives and olive oil

• Nuts & Seeds: Flaxseed meal, chestnuts, hazelnuts, pecans, black tahini

• Vegetables: Purple carrots, red carrots, purple red/potatoes, red cabbage, spinach, red onions, broccoli, orange carrots, red lettuce

• Grains: Red rice, black rice, red & black quinoa, wholegrain rye bread (sourdough)

Just like the different prebiotic fibres above, certain strains of bacteria will consume almost any polyphenol, and some bacteria will have an affinity for a certain type. When you’re aiming for your 40 different foods, try to include foods from all the different colour categories over the week.

4. Avoid the SAD (standard American diet)

Diets higher in saturated fat, protein and sugar encourage the growth of pro-inflammatory bacteria, whilst also starving the anti-inflammatory species that make butyrate and other beneficial substances for our body and brain.

Some studies showed that saturated fat in particular, especially from dairy and coconut oil, binds endotoxin and encourages its absorption into the bloodstream, potentially leading to chronic inflammation.

Dietary fibre in a meal does the opposite - it binds to the endotoxin and also lines the intestinal wall so the endotoxin cannot permeate into our bloodstream as easily. This is likely why saturated fat and protein within the context of a whole foods diet with plenty of fibre from vegetables, fruit, legumes, nuts and seeds reduces its capacity to affect the microbiota negatively.

5. Watch alcohol, especially binge drinking

Alcohol causes endotoxins to flood your system for about 5 hours - which is why you wake up the next day with a low mood and headache - the symptoms of an inflamed brain.

Alcohol also decreases gut permeability, contributing to a "leaky gut" so the endotoxin can more easily enter the bloodstream and reach the brain.

Over time, regular alcohol drinking selects for proteobacteria - a highly pro-inflammatory species. Together with the action of a "leaky gut", you risk more endotoxins entering your system over time, negatively affecting your mood.

Interestingly, in animal studies, many of the negative effects from chronic alcohol consumption were limited after supplementation with oats (a prebiotic fibre)! To us this reiterates the importance of steps 1-3, so start there if you’re not ready to reduce alcohol consumption just yet.

To sum up

Generally, we live in a mutually beneficial relationship with our gut microbiota that promotes health but sometimes our microbiota can become imbalanced and can initiate disease. This can extend to our mental well-being - an imbalanced microbiota can affect our sleep, contribute to body-wide inflammation and increase our risk of anxiety and depression.

Nourishing our microbiota encourages a mutually beneficial relationship and depends on:

• Eating enough fibre & prebiotic foods

• Eating enough polyphenols

• Sufficient exercise

• Sufficient sleep, relaxation & meditation - a managed stress response