Rights: University of Waikato Published 1 July 2011 Download

Dr Juliet Ansell is a Science Group Leader at Plant & Food Research, Palmerston North. Juliet explains how a delicate balance exists between the many different bacterial populations present in the gut. If this is disrupted, the immune system and enteric nervous system are both activated, bringing to the conscious level a feeling of unease.


Dr Juliet Ansell

All the different bacterial populations in the gut are in a kind of balance, and we call this homeostasis, so this just means they are in the right number or right numbers to interact with each other. And this impacts on our health in that, while we are in this sort of homestasis everything is fine. When things get out of balance, that is when we might get sick. So if one particular population increases, like E. coli, that’s when you would have gastroenteritis, and that is when you have got out of balance.

You might have heard of things like probiotic bacteria, yoghurts have Bifidobacteria in them – bifidus or acidophilus – so these are particular species of bacteria that are beneficial to our health. They are really good at degrading the fibre that comes through, so getting all those extra energy and extra health components out of the food. They are also very important in terms of interacting with the immune system, and this is some of the research that we are getting into now.

Good bacteria can secrete things which are antimicrobial. They compete with pathogens, so if you do ingest some harmful bacteria, the good bacteria are actually there physically stopping them from attaching to the gut cell wall. There is a lot more to the large bowel than just taking water out and passing the rest of the waste through. It is a much more metabolically active area than we’ve realised, and sort of every day there is more research being done in this area.

So it relates very much to things like obesity. You know, there is this kind of global epidemic of metabolic diseases – things like diabetes, cardiovascular disease – all these things are actually impacted on by the type of bacteria and the balance of bacteria in our gut. So development of asthma, eczema, things which are known as atopic diseases, it’s also now thought to relate back to your very early acquisition of bacteria in your gut, and how that’s interacting with the immune system. This is because the gut is the first place we see foreign antigens. If your gut knows to respond to something that is harmful, that is good, but it also needs to know not to respond to something that is not harmful. That really comes back down to what bacteria you have and how they are stimulating or not stimulating the immune system.

There is a lot of nerve cells throughout the gut – so the enteric nervous system – and this can relate to mood and anxiety, all sorts of things that sort of you think of as being very much coming from the brain. They are also getting signals from the gut, and so the gut bacteria and the food that we eat is interacting with these nerve cells.

It works the other way as well, so the brain is also having an impact on muscle contraction in the gut. So you know, if you are really, really stressed, you might find that you often get diarrhoea. People think that there might be certain foods you can eat which can actually have a mood-improving effect. We are finding different chemical components of foods mimic the structure of different hormones that are related to mood. The gut is also a major producer of serotonin. Different bacteria can actually stimulate that production, which is feeding back into mood and happiness or wellbeing.

CDC/National Escherichia, Shigella, Vibrio Reference Unit at CDC
EM images courtesy of Dr Sandy Smith, Department of Food Sciences, University of Guelph, Canada
Lactobacillus acidophilus micrograph © Miloslav Kalab, Agriculture and Agri-Food Canada, Ottawa
Footage courtesy of NHNZ Moving Images
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