Faeces-friendly fibre

19 January 2016

Interview with

Dr Erica Sonnenburg, Stanford Medical School, Professor Tim Spector, Kings College London

Your microbiome: that's the word that refers to the hoards of bacteria that live in and on you, and it's extremely important. These bugs affect your health and even your personality. However, in the western world we're missing some diversity. Compared to traditional, non-industrialised tribes and populations we have about a third fewer species of microbe living in our intestines. Theories why range from antibiotics use to cleaner living; but a new study this week has provided evidence that it is at least, in part, down to our diet. Georgia Mills has been shedding some light where the sun doesn't usually shine, beginning with the study's co-author Erica Sonnenberg, who's from Stanford Medical School...

Erica - In our study we really wanted to look at the effect of diet and particularly dietary fibre.  If you look at these traditional populations, they consume an amount of dietary fibre that far surpasses what we consume in the west; something like almost ten times as much, and we know that dietary fibre are really the major currency within our gut.  This is the food our bacteria use to become more abundant in the gut and so we wondered, if you starve your microbes of dietary fibre, what does that mean for that community and we think this may be potentially one of the reasons why our microbiota is so much less diverse than what we see in these high fibre eating traditional populations.

Georgia - How did you test this theory?

Erica - Basically, what we did is we had a group of mice that we colonised with a human microbiota, and then we divided those mice into two groups: one that we fed a high fibre diet  and the other group that we fed a low fibre diet.  And what we found was that the mice on the low fibre diet, the diversity of bacteria in their gut dropped pretty dramatically while they were on the low fibre diet.  We bred them for an additional four generations and what we found was that with each generation, there was a further loss of microbial diversity within the gut of these mice to the point that by the time we got the fourth generation, there were quite a few species of bacteria that were now no longer present in the gut of those mice.

Georgia - What's more, putting the mice back on this high fibre diet doesn't result in those extinct bacteria species coming back; it looks like once they're gone, they're gone.  But is this really a big deal...

Erica - We know that an acute drop in diversity, say from taking a round of antibiotics, opens your gut up to the potential that it would get colonised by a pathogenic bacteria.  So that's, for example, C. difficile, and actually one of the most effective treatments for that is a reintroduction of microbial diversity through a fecal transplant.  Long term, there have been several studies looking at the microbiota of individuals that are obese, or have metabolic syndrome, autoimmune diseases, and in all these cases their  microbiota diversity is much lower than what we see in healthy populations.  Now we don't know if that drop in diversity caused those diseases or is contributing to them, but it does indicate that there's some connection potentially between a low diversity microbiota and many of our western diseases that are rising so rapidly.

Georgia - If this does turn out to be a problem, what about those fecal transplants Erica mentioned. This procedure which involves taking 'poo' from a healthy person and putting it into an ill person to restore their microbiota is now used in many countries across the world.  Tim Spector is the Professor of Genetic Epidemiology at King's College London and the author of "The Diet Myth"; he's been on the show before to tell us about fecal transplants.

Tim - There's usually several ways of doing these transplants; traditionally it was though a tube through your nose, where you put the liquidised poo, essentially, down the nose into the small intestine, or you could pass a tube up through your bottom - given as an enema.

Georgia - If having a 'poo' filled tube up your bottom or your nose doesn't sound like your 'cup of tea,' using capsules of frozen specimens could be the solution.  There was some debate about whether this would work but, research this week from McMaster University in Canada, has shown that transplants can, indeed, work after the bacteria has been frozen - as Tim explained...

Tim - This was a study of over 200 people and they randomised them to frozen samples or the fresh samples and, essentially, found no difference between the two methods. So, it looks like the good news is that you can store these samples for a long time, as long as you store them well they seem to be equally effective, and the evidence seems to show that the way in which you give them doesn't matter too much for severe illnesses.  So you can give them by tube or by these acid resistant capsules - which some bright spark has renamed 'crapsules.'

Georgia - There have been some other, I suppose, worries or concerns about 'poo' transplants because gut bugs have such an impact on our bodies as a whole.

Tim - Exactly.  So as we're discovering that our microbes are essentially key to many of our healthy processes: our immune system, our digestion, our metabolism, whether we get fat or thin and also, increasingly, our emotions so, clearly, any change you're making to the gut microbe could have other far reaching consequences.  There are about two case reports now of people who have received these transplants but have ended up putting on a lot of weight afterwards and it turns out that the donor was of above average weight.  There's also the other potential worry which hasn't been shown yet but in animals you can certainly transmit  some mental illnesses, stress and anxiety so, if you check your donors don't end up as mass murders or psychopaths because ten years down the line it could be causing other problems.

Georgia - As Erica said earlier, our gut bugs are much less diverse in the west so could this 'transpoosion' be the answer?

Tim - A colleague of mine, Geoff Leach, whose co-founder  of the American gut project is actually on a personal quest to make himself the most diverse human on the planet and has, as I explained in some detail in my book, went to Africa and picked a healthy tribesman; hunter-gatherer type from Hasded tribe, and got a donation from him and did a transplant himself using a turkey baster and he claims his diversity increased, but he hasn't yet noticed any major health benefits.

Georgia - Or I'm imagining, any health problems?

Tim - No, exactly; he's a robust Texan, so he's quite tough but, at the moment, most people think he's mad, rather than some people would say he's pioneering.  But, at the moment, we don't know the side effects of whether a microbe, say from Africa, inside us is going to have the same effects.  So what might be great for Africans, might actually be harmful for us.

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