Your guts have a mind of their own. Down there, in your digestive tract, is a brain which works semi-independently of the one in your head. It’s a bit spooky really because the brain in your gut not only thinks for itself, it is also powerfully influential over the way you feel, your mood and sense of well-being. What’s more, it can initiate all sorts of serious disease. A little bit temperamental, the gut-brain must be handled sensitively.
Lining the gut is a network of neurons and neurotransmitters which make up the body’s second brain, technically known as the enteric nervous system. The gut brain oversees digestion, absorption and excretion. Digestion requires a great deal of orchestrating, so it makes sense for the head brain to delegate responsibility for all this activity to another part of the body.
With a large degree of independence, the gut brain is extremely powerful. Consider this: we associate the neurotransmitter serotonin with mood, and lack thereof with depression, yet 95% of the body’s serotonin is found in the digestive tract, where it acts as a signalling mechanism, updating the head brain on what is going on in the gut. So it is no surprise that serotonin in the gut massively influences mood. Those gut feelings are not all in your head.They really are in your gut.
It gets weirder. As well as having a brain of its own, the gut is lined with nerve terminals containing the stress hormones adrenaline, noradrenaline and dopamine. When you experience stress, these hormones are released. Bad, or pathogenic bacteria have developed systems of detecting your stress levels, and using that stress to their advantage. The way they do this is especially cunning, and it involves iron.
For these critters to flourish and do their worst they need iron. Low levels of iron is a major impediment to microbial growth. However, what they need is ‘free’ iron. Iron is not usually ‘free’ – ferric iron in the gut is bound to proteins such as transferrin and lactoferrin. However, the stress hormones in the gut facilitate the removal of iron from the proteins – leaving lots of lovely free iron for these bacteria to feed on. Pathogenic bacteria produce chemicals called siderophores which have an affinity for ferric iron and ‘grab’ it when it is free. This is sometimes referred to as bacterial theft of iron. They thrive, and thus overgrowth of bad bacteria – dysbiosis – is initiated, and so is infection, symptoms of irritable bowel and inflammation. All this also largely explains why intensively reared – and therefore stressed – livestock are so prone to disease, whilst free-ranging, happy hogs, cattle and poultry are much less so.
In short: the gut brain releases stress hormones which cause the iron to be released from proteins; bad bacteria sense this and steal the free iron. Symptoms ensue. If you’ve got digestion problems and you know your symptoms are exacerbated by stress, you might want to consider stress reduction techniques such as meditation or visualisation (imagine shooting all those little deviants) as your first step. Your diet should be high in prebiotics – food to feed the friendly bacteria and fight off the bad guys. Fruit and vegetables are naturally high in prebiotics, in particular the cruciferous family: sprouts, broccoli, cabbage, kale and cauliflower. Beans are absolutely chock full of prebiotic fibre, as are nuts. Avoid the foods which pathogens thrive on – sugar and refined carbohydrates such as white rice, pasta, flour and bread.
Just remember – those microbes are hacking into your emotions. You can’t always eliminate them, but you can disable them.
Gershon, Michael (1999) The Second Brain. Harper Collins.
Freestone, P.P.E., Sandrini, S.M., Haigh, R.D. & Lyte, M. (2008) Microbial endocrinology: how stress influences susceptibility to infection. Trends in Microbiology, 16(2):55-64.
Radek, K.A. (2010) Antimicrobial anxiety: the impact of stress on antimicrobial immunity. Journal of Leukocyte Biology, 88(2):263-277.
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