Some time in the early nineteen eighties, I had the privilege of attending a lecture by Dennis Burkitt on the fibre hypothesis. Burkitt had worked for many years as a surgeon in East Africa, where he not only discovered Burkitt’s lymphoma, a rare lymphatic tumour of the jaw of Ugandan children caused by the same virus that was implicated in glandular fever, he also observed that many of the diseases that were common in the west, were rare in rural Africa. These included diabetes, coronary heart disease, strokes, obesity, bowel cancer, appendicitis, constipation, and irritable bowel syndrome. In his inspiring lecture, Burkitt used a slide of a hot air balloon sailing over the savannah to make the point that he was not the kind of scientist who focussed down a microscope, he adopted a broader vision of epidemiology and landscape. He also noted that the diet of most rural Africans was very different to the highly processed and refined foods commonly consumed in the west. It was lower in fat, sugar, starch and meat, but much higher in fruits and vegetables that contained poorly absorbed fermentable carbohydrates, storage polysaccharides and plant cell wall material, collectively known as dietary fibre. Although he and his colleagues did not understand why, he nevertheless suggested that we might be more healthy and avoid many of the chronic diseases of civilisation, if we adopted a high fibre diet. The Bran Wagon had started to trundle out of Africa and before long a muesli belt stretched tight across the swollen belly of the home counties from Hampshire to Essex.
The high fibre diet resonated with contemporary enthusiasm for a more natural way of living and soon doctors were advising people to buy bags of All Bran instead of prescribing drugs. It was, however, still a decade or so before geneticists sequenced the human genome and realised that colonic microbiome contained 1000 times as many genes and considerably more metabolic potential. We have inside of our colon a vast metabolic powerhouse able to salvage much of the unabsorbed components of our food, free up extra nutrients and energy, produce vitamins and interact with our immune system to influence the health of both the body and the mind.
Separating us from this teeming mass of micro-organisms, is a single line of cells underpinned by the gut immune system, which, like customs and immigration officials, control the passage of aliens and goods across the border. This protective system is restrained in the face of trillions of hopeful immigrants but is at the same time poised to defend the body politic from potential terrorists. If, however, the border is breached and becomes leaky, colonic bacteria can gain entry and influence many different parts of the body including the brain through by releasing of toxins, cell wall material, immune cells and inflammatory transmitters (cytokines) into the blood stream, or by stimulating the vagus nerve and the brainstem, altering the activity in the hypothalamic pituitary endocrine axis and the autonomic (sympathetic and parasympathetic) nervous system. In this way, the gut is the gatekeeper preventing widespread chronic illness and mood changes.
One of the major factors regulating the integrity of the colonic epithelium is the diversity of the microbiome. Depletion and instability can lead to an overgrowth of harmful bacteria, which may damage the cell layer making it more leaky, causing inflammation not only in the rest of the gut but also the rest of the body and leading to a number of symptoms including fatigue, depression, nausea and aches and pains.
It has been estimated that more than half of the variance in microbiota can be accounted for by dietary change though life situations can also act via the neuroendocrine systems to alter gut function and microbial content. It is likely that food and mood work in synergy to activate the gut immune system.
This morning I listened to the Food Programme on BBC Radio 4. Dan Saladino was camping with Professor Tim Spector in Hadza Land in Northern Tanzania, living with one of the few remaining hunter gatherer tribes and eating a diet of tubers, wild honey and berries, particularly the seeds of the baobab tree, and the occasional porcupine. Tim is Professor of Genetics at Kings College, London. His area of special interest in the microbiome. While lodging with the Hadza, he collected samples of his own faeces. When he analysed these back in London, they revealed that in three days the diversity of his microbiome had increased by 40% and the species that changed the most were Akkermansia mucinophilia that prevents obesity and Faecalibacterium Prausnitzii that damps down the gut immune system.
The concept of chronic inflammation caused by dysbiosis generates new opportunities for treatment. You could take probiotics, but there is no strong evidence that they can seed the gut or lead to long term microbial restoration or relief of symptoms. Faecal microbial transplant might be a better option. It is already used for antibiotic associated colitis and some cases of ulcerative colitis, but needs more investigation and regulation for common illnesses like IBS. Changing the diet to restore microbial diversity and reduce intestinal permeability and inflammation would seem more acceptable, but what is an anti-inflammatory diet? The answer is a mainly vegetarian diet, with high intakes of pulses, fruit, brassica, some seeds, garlic, turmeric, ginger and some fish and a little lean meat. It is said that there is a 400% increase in pro-inflammatory cytokines after eating a Big Mac, whereas a healthy anti-inflammatory diet supports the production of the gut-brain transmitter, serotonin and the restorative short chain fatty acid, butyrate. Nutritionist, Mike Ash, a supporter of this diet suggests that a good start would be to eat a bowl of stewed apple with cinnamon every morning.
But hang on a bit: I am sure you have not failed to notice that this anti-inflammatory diet, which would work to restore microbial diversity and reduce intestinal inflammation and sensitivity contradicts the concept of a low FODMAP diet. How can that be? Well, the low FODMAP diet is not a cure for IBS, it is a symptomatic treatment, a dietary sticking plaster that reduces the gas production and gut reactions that cause symptoms in a sensitive gut, but when strictly applied, it depletes the microbiome. It can, however, buy time while measures to reduce intestinal sensitivity take effect, such as stress reduction, mindfulness, reduction in alcohol, and maintaining a healthy intake of poorly absorbed ‘polysaccharides’ such as ispaghula, or oat based porridge. Then as the symptoms come under control, the health of your colon might be maintained with a more long term anti-inflammatory diet. A low FODMAP diet is not for life nor even for long term. So, it seems to me that, having established some symptom relief, efforts might usefully be focussed on easing up on the main gaseous culprits such as onions and pulses while maintaining healthy intake of tolerable anti-inflammatory vegetables. The same principles would probably apply to people with gluten sensitivity.