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Your guide to the microbiome

Dr Saliha Mahmood Ahmed offers some tips for digestive health and happiness

The magical interplay between human beings and the bugs that live inside us is at work from cradle to grave and is, therefore, well worth our time and understanding.

The human gut hosts around 40 trillion microbes. For those needing to conceptualise that number, it’s a four followed by thirteen zeros; it outnumbers the stars in the Milky Way (a mere 300 billion), all the fish in all the oceans on earth (around 3.5 trillion) and even the individual cells in your body (around 30 trillion). Thirty trillion human cells and 40 trillion bacteria is almost a one-to-one ratio of human cells to microbes, and this gargantuan mass of microbes weighs around 2kg. Because it would be a pain to remember the names of all these microbes, we refer to them collectively as our gut’s microbiota.

The human body forms a landscape of microbial habitats that is more diverse than any landscape on earth, and each individual’s microbiota is unique – almost like our very own personal fingerprint. The genes that make up the microbiota in the human body are termed the ‘microbiome’.

There are three main categories of ‘good’ bacteria (Bacteroidetes, Firmicutes and Prevotella actinobacteria, in case you are interested), and we all possess different strains of these three groups (among other bacteria) in different ratios, as well as a range of fungi and viruses.

Generally, the more diverse your microbiome is, on a scale called the Simpson index, the better.

Gut microbes have co-evolved with us over time. They love us because our guts provide the perfect warm, wet environment for them to flourish, and over millions of years of human evolution, they have become an essential part of our digestive process. What’s more, their help is not limited to digestion; the microbes of the large bowel have been shown to influence our levels of immunity, and also to affect our bodies’ ability to keep inflammation contained, stimulate the local nervous system and help increase the beneficial cell turnover on the lining of the gut wall. They’re just so talented.

A beautiful, balanced equilibrium exists, therefore, between our bodies and our microbiota, but there can often be collateral damage in our fight against other ailments. For instance, a course of antibiotics or the explosive laxatives required for a colonoscopy can practically wipe out our gut microbiota.

Current research suggests that the gut microbiota is influenced by diet, and that some microbiota are ‘better’ and more diverse than others. A healthy, diverse microbiota has been linked with a variety of health benefits, like lower risk of heart disease and diabetes, obesity and metabolic disease, among others.

Optimising gut health naturally

One way of diversifying the microbiota is to introduce a greater variety of foods into our diets, particularly those that are plant based. Now, I am not advocating switching to an exclusively vegan or vegetarian diet, but instead encouraging (gently, I hope) the introduction of a greater assortment of vegetables into your existing regime. The judgement call on whether to include meat or not is one that everyone needs to make themselves, based on their own lifestyle, beliefs and taste preferences. But it is a fact that eating more plant-based foods will make a positive difference to your microbiota, and relatively rapidly. Studies conducted at Harvard University assessed the microbiota of healthy volunteers who were switched to either a plant or meat-based diet and found that the microbial composition of both groups adapted rapidly to the shift.

Cultivating your gut microbiota

Another way of cultivating the microbiota is to treat your gut to a diet rich in prebiotic and probiotic foods.

Prebiotics are foods that are known to promote the growth of healthy gut bacteria, and can include wholegrains, apples, bananas, leeks, asparagus, dandelion greens, cauliflower, broccoli, Jerusalem artichokes, chicory, honey, garlic, seeds, nuts, lentils, cocoa and green-tea extracts.

In contrast to prebiotic foods, probiotics are foods that actually contain live bacteria. The intention is that these bacteria find their way into the bowel, where they can make their home and lots of bacteria babies. The theory is that eaten in the right quantities, probiotics really can help the gut microbiome stay healthy.

Here are some popular probiotic products (this is by no means an exhaustive list):

It is undeniable that the food we eat exerts a huge influence on the composition of the gut microbiome. I like to think that through the food I choose to ingest, I am, in fact, communicating directly with my gut bugs, nourishing them, creating a comfortable environment for them, allowing them to thrive; and in turn, they are helping me to flourish. Thus, eating healthily and happily is perhaps as much about feeding our gut bugs as it is about feeding ourselves.

Extracted from Foodology: A food-lover’s guide to digestive health and happiness by Dr Saliha Mahmood Ahmed (£20, Yellow Kite)

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