When I went to medical school in the 1970s, the only microbes we were taught about were those that caused an infection. Although we were told there were large numbers of bacteria in our gut, referred to as normal flora, we were also told that they were harmless commensals, thus could be safely ignored.
I subsequently trained as a specialist medical microbiologist. It was becoming increasingly clear that the normal flora could actually be beneficial in many ways.
Our hospitals were plagued by outbreaks of Clostridium difficile diarrhoea, usually affecting patients previously treated with antibiotics. It turned out that the antibiotics had upset the normal balance of bacteria in our gut, thus allowing the acquisition and overgrowth of Clostridium difficile.
We are now ever more aware that the trillions of microorganisms in our gut, nowadays referred to as the gut microbiome, are actually quite important in keeping us healthy; whereas changes to the microbiome could be associated with a number of medical conditions, including possibly cancer.
We sometimes think of diseases as the consequence of bad luck. However, luck has a limited role. Diseases are mostly a consequence of the interactions between genetic predisposition, environmental factors and, sometimes, an imbalance of the microbes that make up our microbiome (dysbiosis).
The bacteria in our gut are not just bystanders: they influence the release of compounds that can reach and affect the function of distant organs, including possibly the brain. One of the ways in which dysbiosis could lead to disease is by triggering low-grade inflammation.
Food for life
What we eat is important and is the topic of a new book (Food for life, 2022) by Tim Spector, a professor of genetic epidemiology.
Tim Spector argues that to understand how food affects our health, we also need to understand how it does affect our microbiome. His main recommendation is to eat plenty of vegetables and fruits, and in a great variety, aiming for thirty different types each week. He also suggests choosing plant foods with a high contents of polyphenols and fibre, and eating regularly fermented foods (like yogurt, some cheeses and kombucha).
Tim Spector recommendations are somewhat similar to the Eatwell guidance provided by our government. However, he puts more emphasis on a reduced consumption of ultra-processed foods, which have a high content of additives, sugar, salt and fats and have been formulated to stimulate our appetite and make us eat too much.
Eating healthily can be difficult. The scientific evidence has changed over time and is not easily grasped. Individual published studies can be misleading, whilst it is difficult to find reliable websites with good up-to-date summaries. As for the food labels, they may be confusing.
We are continuously targeted with unhealthy food marketing and by the lure of fast-food and take-aways. Tim Spector recommends that we should cook and have communal family meals more frequently. We do not need to eat healthily every day: what matters is what we do most of the time.
Tim Spector’s book makes multiple references to ZOE, a personalized nutrition company of which he is a co-founder. This is mentioned as a conflict of interest in the scientific articles to which he has contributed, but not in his book.
ZOE charges customers £ 259.99 for a set of tests that include blood glucose, blood lipids in and a gut microbiome test. ZOE also offers a charged-for subscription to a dietary support plan.
I can see the advantages of personalised diet that takes into account blood lipids and glucose tests, but I am not convinced that gut microbiome tests are beneficial at this stage of our knowledge. We just do not know yet precisely what microbiome changes play a causative role and for which conditions. Neither we know precisely what is the ideal microbiome.
I would strongly endorse Tim Spector’s diet advice. A good diet seems also to be conducive to a good microbiome. As for microbiome testing, I think we are going to hear more about this, and it might well become an accepted beneficial test in future.