This is an article that some readers, particularly those of a fainter-hearted disposition, might want to avoid. It’s about a big movement that some people might find a tad distasteful.
For those of a more intrepid nature: we’re going to be looking at something called “microbiome” and the impact this is having in a wide range of medicine and research. I’ll also make mention of one of the most disgusting procedures in medical practice that involves something you (hopefully) do every day – but more of that later.
First: microbiome. This is the collective name for the various species of bacteria, fungi and other microorganisms (and their genomes) that inhabit the human body.
While we’re all familiar with the idea that our gut is colonised by various types of bacteria, there are microbiota making themselves comfy all over the body – not just the gastrointestinal tract but the genitalia, the lungs, the skin, nasal cavities and more. What is interesting is that medical science has suddenly started to figure out that these different populations might do more for us than we’ve previously realised.
In particular there has been a renewed interest in the relationship between these populations of bacteria and our immune system. The dominant view has been that the gut bacteria have a direct and important role in our digestive processes. Indeed there’s a whole industry of yoghurty health drinks out there based on the simple idea that we want to support "the good bacteria".
The bacteria in your gut are having effects on the immune system globally, not just in the local environment of the gut. The implications of this are only just beginning to become clear.
These good guys help with our, ahem, movements and help reduce the incidence of digestive problems. Partly through the process of fighting off the “bad bacteria” – things like Clostrodium Difficile and other pathogenic nasties – and partly through helping us directly in the digestive process (providing us with many essential nutrients along the way).
However, it now appears that the bacteria in the gut are intimately involved in the systemic functioning of our immune system. In other words the bacteria in your gut are having effects on the immune system globally, not just in the local environment of the gut. The implications of this are only just beginning to become clear.
A nice example of some recent work on this looked at two different mouse models of cancer – one with a genetic predisposition to breast cancer (analogous to women with a BRCA1/2 mutation), and one with a tendency to develop cancer after eating a ‘fast food’ diet.
What was interesting was that in both cases mice fed on probiotics developed fewer cancers than the control mice. In both cases it turned out that feeding with bacterial “good guys” had systemic immune effects that helped protect against mammary tumours. In case you didn’t get that, let me run that by you again: mice bred to develop breast cancers were protected against cancer development by being fed probiotics. This isn’t the only finding of interest to cancer researchers. It turns out that response to chemotherapy is also linked to our microbial fellow-travellers. The response to the chemotherapy drug cyclophosphamide (a standard and widely used anti-cancer treatment) is better in mice with a healthy population of gut bacteria.
Mice treated with antibiotics, or bred to be free of bacteria, fare less well. And the effect is not limited to cyclophosphamide – again it looks like there’s something significant going on in the relationship between bacteria and immune cells.
Fat mice and fat people have something in common
But enough about mice. What about what’s going on in us humans? It turns out there’s something directly relevant to the discussion of diet and obesity. As mentioned briefly in my article that looked at the paradox of rising obesity and falling calorific intake, it may be that gut bacteria is part of what’s going on.
It is known there are marked differences in gut ecology between lean and not-lean individuals. Crucially, some classes of bacteria are more efficient at processing lipids (fats) than others, which means the same fat intake can result in radically different calories being absorbed by different individuals based on their gut ecology.
The most famous experimental example of this took samples of gut bacteria from sets of human twins where one was large and the other not, these bacteria were implanted into mice fed a low-fat healthy diet. Mice implanted with “large twin” bacteria got chunky, those with the “lean twin” bacteria didn’t. The results were repeatable and consistent – even with the same diet, the mice grew large or not based on the bacteria they had been implanted with.