Opening your bowels is a basic function of life. But despite the fact we all do it, pooing is not often thought to be a topic suitable for polite conversation. However, recent popular

interest in gut health and the composition of poo – as well as the bacterial populations that live within it – have helped to put bodily functions more on the map. And these days, more and

more people are wondering how often you should go, what happens if you don’t go enough and how you can influence the composition of what is passed. In the late 1980s, Professor Ken Heaton

and colleagues conducted a survey of the population in East Bristol, in the UK. They reported the common wisdom that “99% of people defecate between three times per week and three times per

large bowel responds and we should go to the toilet. Through a range of hormones we will experience a “call to stool”. Most of us, however – from the time we can walk – suppress this call,

so once a day or less has become the new norm. Urgency, diarrhoea, and constipation can all be features of not going to the toilet enough. And associated with this “relative” constipation

are symptoms of bloating, pain and variability of bowel habit. A simple test of how your bowels are working is the “sweetcorn test”. By swallowing a handful of raw sweetcorn – which is not

absorbed by the body – the brightly coloured kernels can be easily seen in your motions. This is an easy way to assess your own mouth-to-anus transit time. It should probably be about eight

hours. THE COMPOSITION OF POO Poo is made up of 75% water. The rest, which is the solid stuff, is up to 50% microbes plus cells that are shed from the bowel lining and food residue. The

collective name for the microbes that live inside us is the microbiome and at one time, it was thought that the bugs outnumbered our cells by ten to one. Recent data suggests this may be

closer to a ratio of 1.3 to 1 but this will obviously depend on how often you go. Bacteria, viruses, fungi and single cell microbes make up the microbiome and all may be critical to our

health and well-being. From a positive perspective, the bugs in our guts not only breakdown undigestible foodstuffs, but they also produce critical nutrients, prevent certain infections and

contribute to the development of our immune defence systems. However, obesity, type two diabetes, high blood pressure, inflammatory bowel disease, autoimmune disorders and mental health

problems have all been linked to dysbiosis – or change of the microbiome. GUT FEELINGS Establishment of our microbiome starts at birth and is influenced by the way we are born – either

vaginally or by Cesarean – and initially fed. By the time we start eating solid food, we are well on the way to establishing our adult microbiome. What we subsequently eat can have an impact

on the composition, although this effect may be modest. Our diets also may influence the metabolic products of our microbiome – these are the chemicals that the individual organisms produce

– which can also have an impact on us as the host. Fibre, fat, sugars, artificial sweeteners have all been shown to modulate the composition of the gastrointestinal microbiota. Experimental

data suggests that prebiotic fibres change gut microbiota and increase hormones that tell us that we are full. Current ongoing research has also shown that antibiotic induced microbial

imbalance is associated with changes in bitter taste expression – which influences the foods we prefer to eat. All these relationships are complex, and scientists are just beginning to

understand their full impact. The ultimate way to alter our microbiome is a faecal transplant, where you take on board the poo from someone else. Unpleasant as this may sound, encouraging

data is emerging on the use of poo in the treatment of gastrointestinal infections such as clostridium difficile, early diabetes, multiple sclerosis and inflammatory bowel disease. But it

may still be a while before you can buy prized poo over the counter in your local supermarket.