The mighty microbiome

Professor Robert Thomas explains how prebiotics and probiotics can help to promote gut health

Trillions of bacteria, fungi and viruses reside in or on our bodies, particularly around the gut, skin, genitals and lungs, which collectively form our microbiota. It’s an incredible fact that over half of our cells’ genetic material is derived from these alien organisms.

It should be no surprise, then, that the healthy bacterial component of our microbiota plays a key role in ensuring our bodies’ defences and functions run smoothly. Yet it is becoming clear that in the UK and other western countries, our diets and daily habits are creating woeful deficiencies. People living in rural regions of Africa and South America traditionally have a wholesome, diverse gut flora, yet after just a few months of a western-style diet, their levels of healthy bacteria plummet.

The biodiversity of the gut and skin microbiota deteriorates with age, causing anti-inflammatory (Bacteroidetes) bacteria to reduce and pro-inflammatory (Firmicutes) bacteria to increase. Other factors that influence abnormal bacterial growth, especially in the gut, are the food and drink we consume, recent illness, medical treatments or changes to our habits and diet when travelling abroad.

Probiotic bacteria

These are live microorganisms that occur naturally in many fruits and vegetables, as well as in a range of fermented foods. Probiotic bacteria have a range of health benefits and good sources include:

  • Live yoghurt and kefir
  • Aged or blue-veined cheeses
  • Miso, kimchi and tempeh
  • Sauerkraut and pickled vegetables

To boost your gut health, try to eat one or more of these probiotic-rich foods every day. Matured cheeses should be eaten in moderation as, despite being an excellent source of healthy bacteria and fungi, they also have a high cholesterol content.

Prebiotic soluble fibre and phytochemicals

Prebiotics are types of fibre that feed your friendly gut bacteria and promote the formation of healthy colonies in the lower bowel gut. Some prebiotics can impede Firmicutes from sticking to the gut wall so create more space for Bacteroidetes to grow. Others can preferentially feed the Bacteroidetes and starve the Firmicutes. They can protect healthy Bacteroidetes bacteria from enzymes in the saliva and stomach, and some even have natural antibiotics that selectively kill Firmicutes but not Bacteroidetes. So, when considering strategies to improve gut health, it’s just as important to enhance your prebiotic intake as the probiotic intake. The two main sources of prebiotics are phytochemicals and soluble fibres.

Phytochemical prebiotics

Phytochemicals are considered prebiotics because they feed the good bacteria in your gut. Healthy probiotic bacteria are responsible for the extensive breakdown of the original phytochemical structures into biologically more active phenols, which can then be absorbed more efficiently. These phenols are used as energy by the intestinal bacteria so they support the gut growth, repair and wall integrity. This process also feeds the Bacteroidetes, but not the Firmicutes, which tend to use sugar as energy instead. Some prebiotic phytochemicals contain natural antibiotics, which improve the ratio of healthy to unhealthy bacteria as they affect Firmicutes rather than Bacteroidetes. Mushrooms, in particular, are good sources. Resveratrol, the red pigment in pomegranate and grapes, is a particularly good prebiotic, which explains why studies involving red wine, in moderation, have shown an improved gut health. Turmeric has long been used in traditional medicine to treat conditions ranging from indigestion and arthritis to depression. It is quite poorly absorbed in the small gut so enters the bacteria-rich large bowel. Tea and cocoa (without sugar) are rich in flavonol polyphenols, which have demonstrated significant growth inhibition of pathogenic bacteria while maintaining the growth of healthy butyrate-producing bacteria such as Bifidobacterium and Lactobacillus.

Soluble fibres as prebiotics

Certain fibres work with phytochemicals to encourage healthy bacterial growth. The two main categories of soluble fibres are the non-fermentable soluble fibres which include gums, psyllium, ispaghula husk and pectins, and fermentable soluble fibres such as the resistant starch inulin and carbohydrate chains such as oligosaccharides. Soluble fibres provide nutrients for the microbiota within the large gut, as well as increasing faecal bulk which makes it easier to pass. The fermentation of soluble fibre by healthy bacteria produces butyrate, which enhances digestive function, gut immunity and gut health. Beta-glucans, found naturally in the cell walls of cereal plants and fungi, is a fermentable soluble fibre that is particularly helpful for gut health.

Other food sources of soluble fibres include grains, flaxseed, sesame seeds and peanuts, many of which also contain lignan polyphenols. These are converted to their bioactive lignan metabolites which, as well as being anti-inflammatory, have anti-oestrogenic properties. Colonisation of the gut with these lignan-metabolising bacteria has been shown to protect the gut from carcinogens which normally induce multiple bowel cancers. Bananas are rich in soluble fibres and have been shown to promote the health of the gut by preventing potentially harmful pathogens sticking to its wall, preventing infections from pathogenic bacteria such as Salmonella and Clostridium.

Good-quality probiotic supplements

When considering the evidence for probiotic supplements, it is important only to take into account data from studies that involve individuals whose microfloral profile is likely to be suboptimal to start with, due to age, obesity and other lifestyle factors already summarised above.

For those who are likely to have a poor gut bacterial profile, a good combined probiotic and prebiotic supplement can increase gut diversity, which results in lower inflammation and better gut integrity.

In terms of safety, a well-designed probiotic supplement should contain bacteria that are (or should be) already present in a normal digestive system. It should not be a surprise, then, that even with the large quantities of probiotic supplements consumed around the world, the numbers of opportunistic infections that result from probiotic supplements are negligible. They have been used in trials involving severely ill patients in intensive care or on chemotherapy and have demonstrated benefits such as a significant reduction in diarrhoea and an improvement in other symptoms without side effects. The main risk posed by a probiotic supplement is a contaminated supply, so it is very important to obtain them from a reputable source. Make sure that the ingredients are clearly marked on the label and look for blends produced by a long-established, reputable manufacturer with a high-quality-assurance track record compliant with EU, UK and US standards.

With the growing use of immunotherapies in medical treatments, understanding the microbiome is gaining prominence. A one-size-fits-all approach is unlikely to succeed when it comes to restoring deficiencies in an individual’s microbiome. In the future, it is envisioned that a tailored probiotic regimen could help maintain or restore a person’s unique microbial ‘fingerprint’, and, in doing so, substantially improve responses to life-saving treatments.

Extracted from How to Live: The Groundbreaking Lifestyle Guide to Keep You Healthy, Fit and Free of Illness by Professor Robert Thomas, Short Books, £14.99.

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