All about the microbiome: How to have a healthy gut and boost your body's immunity

Mushrooms, bone broth, sourdough... your stomach is the way to well-being. Time to recalibrate your gut instinct, explains Rebecca Newman

We are now at that time of year when winter bugs flourish and commuting becomes a mission to evade spluttered germs and viruses. Wouldn’t it be great to find a way not to get sick this winter that didn’t involve a hazmat suit or emigration? 

As it happens, scientific research affords us an ever-more sophisticated understanding of how to stay well, as it casts light on the vital role played by the gut and its bacteria. 

First up, the science bit — 70-80 per cent of our immune system is located in our gut. Hugely important to this system are the trillions of bacteria (2kg worth, the weight of a small rabbit) that live there. This bacteria forms a physical barrier that covers the gut wall, helping to prevent viruses and other undesirable illness-causing microbes entering the body. It also stimulates the lymph system that lives within the gut wall to produce lymphocytes (the white blood cells that fight infections). 

‘Increasingly, we’re able to measure what goes on in the gut wall,’ says clinical nutritionist Peter Cox of leading London health clinic, Omniya. ‘This provides a greater understanding of what is required to improve gut-barrier function and encourage immune modulation [that is, the modification of the immune response]. This understanding is one of those exciting developments that occasionally come along and will genuinely change how healthcare is delivered.’

Hooray to that. But for those of us wanting to avoid colds right now, what to do? The first step is to encourage a healthy gut ecology by eating probiotic foods (that contain the ‘good guy’ bacteria) and prebiotic foods (that the good bacteria like to eat). 

‘For probiotics, you want to be eating fermented foods daily, such as sauerkraut, miso or kimchi,’ says nutritional therapist,  Eve Kalinik. ‘Kefir — fermented milk — is excellent, and the Daylesford version is delicious. Consider using kefir instead of milk or yoghurt.’

In terms of prebiotics, Kalinik recommends oats, beans, leeks, kale, rocket, onions and garlic. ‘As well as being prebiotic, garlic is also a fantastic antimicrobial,’ she adds. ‘But people often don’t realise garlic’s antimicrobial properties are destroyed in cooking.’ Her solution? ‘You toast sourdough bread — which is made by fermentation — then add raw garlic mashed into unpasteurised butter [more beneficial microbes, available at most supermarkets] with parsley [full of gut-supporting nutrients].’ You won’t be bitten by many vampires or kissed by anyone else, but you won’t be getting a cold. 

The ancient Jewish cure-all, bone broth, is back in fashion. And its effectiveness has now been proven: it contains an amino acid called L-Glutamine, which helps repair the fabric of the gut wall.

‘Our ancestors ate over 100 foods daily, whereas now many of us struggle to eat more than 20 different foods a day,’ continues Cox. ‘Inevitably, this increases the likelihood of damage to our gut walls due to repetitive exposure.’ 

Diets rich in sugar, coffee and alcohol can also contribute to a ‘leaky gut’, in which particles of food or other toxins leak through the gut wall. Our immune system must exert itself to gobble up this flotsam of food, instead of gobbling virus particles and bacteria.

‘Damage to the gut wall also appears to increase the risk of autoimmune responses,’ Cox adds, referring to a group of complaints such as asthma, allergies, arthritis and irritable bowel syndrome (IBS) — all of which are on the rise.    

Happily, bone broth is delicious. To power it into the immunity big league, you’ll of course be adding a range of prebiotic leafy-green veg. 

You might also consider mushrooms. Like bone broth, mushrooms have long been celebrated in other cultures for their restorative powers. Today, biochemist and lecturer at University of Westminster, Martin Powell, is working to promote the hundreds of clinical trials that demonstrate their health-giving properties. 

‘Mushrooms have significant therapeutic potential, particularly regarding immunity,’ says Powell, whose books include Medicinal Mushrooms: The Essential Guide and a clinical equivalent used by doctors worldwide. A mushroom’s curative effect comes from the polysaccharides (the carbohydrate structure in its cell walls) ‘which bind to receptors on our immune cells, triggering widespread immunological changes which help to restore healthy immune responses’. 

In layman’s terms, if our immune system is weakened, the polysaccharides will encourage it. Equally if our immune system is overactive, for example with hay fever, they will calm it and bring it back into a balanced state. 

Powell is absolutely not preaching a Steve Jobs-style departure from Western medicine. But, listing trials (such as a 2012 study by University of Florida finding shiitake enhance immunity, or a 2013 Taiwan study linking reishi mushrooms to cancer-cell death) he is passionate enough to educate as many people as possible. ‘We ignore Eastern approaches, such as the use of mushrooms, at our peril,’ concurs Cox. 

Katy Perry is convinced. She has said she regularly goes on an ‘M-Plan’ diet, in which one meal a day is mushroom-based, saying ‘mushrooms in general are so healthy and good for you, I can’t get enough’. Since cooking does no harm to their active components, consider stir-frying them or adding them to soups and stews. Shiitake have good anti-viral properties, while the chaga mushroom is celebrated in China and is available in wonderfully savoury Chaga Tea (£23.99 at If you’re feeling pinched, grab a bag of button mushrooms at the market — Powell assures me even these wallet-friendly, mild-tasting funghi will do you good.

What about supplements? Clearly the right ones can be helpful but care must be taken, especially when it comes to mega-dose powders, which promise mega-effects. 

‘Many of the high doses of vitamins proffered by supplement brands are excreted in your wee; the body simply can’t absorb it,’ says nutritional therapist Henrietta Norton. ‘Or worse: taking too many of certain nutrients engenders “competitive absorption”,’ (cells can only absorb so much; if they are stuffed up with vitamin C they may be unable to absorb other critical trace nutrients). 

Kalinik recommends Wild Nutrition Vitamin D — vitamin D is used by the body’s immune cells, and many British people are deficient in winter. Or try Wild Nutrition’s Immune Support Formula, which includes vitamin D, and also a selection of powdered mushrooms (£26 at Another excellent choice is Cellution, a supplement specifically designed to support the health of immune cells (£35.50 at

If diet and nutrition are critical to staying well, clearly so is lifestyle. 

‘We must not lose sight of the patterns of behaviour which support our immune system,’ continues Cox. This includes ‘getting enough rest and sleep to enable our immune to recover overnight. Also managing stress with yoga or meditation’, as stress will throw your hormone levels out of whack, which in turn affects the rest of your physiology. 

At its most basic then, the goal is to eat a variety of foods and make time for resting, and for digesting. ‘If we aren’t taking time to chew and then digest before rushing off to the next meeting, we may miss out on all the goodness,’ sighs Kalinik. ‘We are not what we eat. We are what our body is able to absorb.’ 

So, welcome to a brave new world where you chuck the mega-dose flu defence powders and embrace mushrooms on sourdough toast and where taking time to stop and relax is to be encouraged. You’ll not only boost your chances against the winter lurgies, but might give your health a tremendous boon for life.


Original article published in Evening Standard Magazinei, in July, 2017