For someone who has spent a good portion of her professional life studying human excrement in a bid to discover more about 'planet you', Dr Linda Thomas is remarkably enthusiastic about her day job.
But faeces don't tell the whole story, says Thomas who, as science manager at Yakult UK, knows a thing or two about gut bacteria, good and bad. "Faeces provide a reflection of what is going on in the final stages of the gut but they do not show what is happening further up the digestive tract. For that, you have to use biopsies. In fact, some of the major work done in this area by Dundee University has been with sudden death road traffic accident victims where you can find out what is actually going on in the upper part of the gut."
It's not a job for the faint-hearted then? "Once people find out what I do, they always feel the need to tell me how their bowels are functioning", says Thomas. "And frankly, I don't want to know. But I am still passionate about probiotics. Your gut flora is really important; the surface area of your gut is 200 times the area of your skin, so there is a huge number of defence systems in the gut associated with the gut flora."
For cynics suspecting that our guts can function perfectly well without the ingestion of a daily dose of 'good' bacteria, Thomas points out that, until relatively recently, this was probably the case.
However, several factors have combined in the last 50+ years to upset the delicate balance of our internal microflora, she claims. "Today, we just don't consume the wide range of lactic acid bacteria that we used to; we're also taking antibiotics - which effectively wipe out large amounts of good and bad bacteria alike; we live a lot longer and we have a poor diet. Basically, we are not very nice to our guts."
She adds: "Do perfectly healthy people need to take Yakult? Well, I drink a bottle every day and I am healthy with a good working gut; the reason I take a probiotic is because I want to stay that way long-term."
Perhaps the secret to the commercial success of probiotics as a functional food is that they provide short-term as well as long-term benefits, says Thomas, who spent the first part of her career focusing on 'bad bacteria' at the central public health laboratories at Collingdale, UK, and the latter part exploring friendlier varieties at Cardiff University, Danisco and now Yakult.
On the one hand, she says, there is a wealth of human intervention studies to suggest that Yakult's Lactobacillus Casei Shirota strain could provide a range of long-term health benefits from reducing the risk of certain cancers to boosting the immune system. On the other hand, it also addresses more immediate symptoms of digestive discomfort - which offers punters an immediate bang for their buck. "It's anecdotal, but many people with irritable bowel syndrome who are taking Yakult are experiencing a tangible benefit. We have very loyal customers."
But the exciting thing about Lactobacillus Casei Shirota, says Thomas, "is that the research just keeps on delivering new things - and we've been studying it for 70 years. There were two major papers based on UK research that we put out last year I am really thrilled about. One was looking at the immune reaction of rhinitis [runny nose] sufferers - there were indications that the immune response was much better with people on Yakult.
"The other was a small trial at University College Hospital in London on people with cirrhosis of the liver. These people typically have an impairment of the immune system that makes them susceptible to infection. We worked out that what was happening was that there are high levels of endotoxins in the blood that aren't cleared by the faulty liver, but are also probably the result of poor gut barrier function and a poor balance of gut bacteria. For patients taking Yakult, this immune defect was completely restored, which was incredibly exciting."
Given that endotoxins have also been linked to several obesity-related diseases, she adds, probiotics could also play a key role in tackling these in the future.
More immediately, says Thomas, who also has a PhD under her belt exploring E.coli, "there is strong data showing that probiotic dairy products that contain Lactobacillus Casei strains could reduce the risk of people developing antibiotic associated diarrhoea in hospital, particularly the elderly"
The proof is in the pudding
But which probiotic-related health claims are likely to gain approval in Europe when the infamous 'article 13.1' list of approved claims is published in 2010 under the Nutrition and Health Claims Regulation?
For a start, says Thomas, there will be no general claim about 'probiotics' per se. "Claims must be strain specific, which puts us in a strong position as we have spent 70 years focusing solely on one strain."
Thomas will not speculate, but industry sources predict several claims about L. Casei Shirota will probably make it on to the article 13.1 list, from generic claims about improved bowel habits and gut health to something more specific such as 'helps support the body's natural defences by supporting balanced gut flora and gut barrier function'.
As for article 14 claims (which cover disease risk reduction and children's health and development), Thomas will not discuss Yakult's submissions, but says it is not beyond the realms of possibility that cancer risk reduction claims could be substantiated in future, although there are not currently many biomarkers in this area that are "widely accepted and validated"
She adds: "Ultimately, you want to look at endpoints - whether people you are studying actually develop a disease, but biomarkers are also important. For instance, we have some very nice placebo-controlled trials on healthy people where we have been analysing the harmful metabolites in their colons and we can see that those taking Yakult have a lower level of certain harmful enzymes, toxins and carcinogens, which would be markers for long-term gut health."
To substantiate food heath claims, you also need to conduct trials on healthy, not sick, people, she points out. "We've had a lot of trials looking at immune parameters for different conditions and different population groups but they have to be translated in to a clinical outcome where you actually measure something.
"But we also have actual colon cancer and bladder cancer trials in Japan. We have one four-year trial where tumour progression is actually an endpoint, which is very very unusual."
So where is probiotic research heading? Into the stratosphere, says Thomas. "The blessing and the curse in this area is that so many people are working on it - either in probiotics or the analysis of the intestinal microbiota." Perhaps the most exciting work is connected to the US-based human microbiome project - which aims to characterise the human microbiota, she says. "They will actually DNA sequence a lot of the bacteria in the colon that have never been cultured before.
"The challenge has been that, up until relatively recently, we've had to culture faeces and grow up the bacteria. As a result, we weren't growing a lot of the bacteria because it was too difficult as the major organisms in the colon are all obligate anaerobes [anaerobic organisms which won't grow if there is any oxygen present]. So the new DNA-sequencing methods that are coming out to do really big arrays of assays are going to help a lot."
'Model guts' can also play a useful role in research, she says. "They can't replicate the cell walls and colonisation sites but they can try and replicate the stream of nutrients through the intestine, the transit time and the pH." But what is really contributing to convincing leading scientists and healthcare professionals about probiotics is the "work at the genetic and molecular level to elucidate what is actually happening in terms of the stimulation of the immune system", she says.
For the rest of us, a more simple explanation may suffice, she says: "If you pack a garden [your gut] with nice flowers ['good' bacteria], you'll squeeze out the weeds ['bad' bacteria], and if you feed that garden with some compost [prebiotics], you'll help the flowers grow."