Tuesday 21 January 2014

Probiotics and Cancer Risk

The link between diet and cancer is complex enough for most people, but add in a genetic predisposition to cancer and the complexities go through the roof. While there are plenty of people out there with healthy diet plans and advice on what to eat to avoid cancer, when it comes to family histories full of cancer, doesn’t genetics trump diet? Is it really possible to reduce your cancer risk in spite of your family history? I am convinced that genes do not rule your destiny. Indeed one of the key things in my two compartment theory of Li Fraumeni Syndrome is that there are ways to massively reduce the risks of cancer even for people with mutated TP53 tumour suppressor genes. The same applies to women with BRCA1 or BRCA2 mutations – while there’s a definite elevated risk of cancer, it does not mean that there’s nothing that can be done to reduce the risks.

Which is why a recent paper published in the International Journal of Cancer makes for such interesting reading.  The title of the paper pretty much says it all:

Beneficial bacteria stimulate host immune cells to counteract dietary and genetic predisposition to mammary cancer in mice

Sadly this is not an open access paper that we can all read online. However, the authors of the paper had previously looked at the influence of probiotic bacteria on obesity, and that paper is accessible to all for those who are interested:

Microbial Reprogramming Inhibits Western Diet-Associated Obesity

In that work the authors fed mice a conventional ‘fast food’ diet and monitored the response – a set of obese mice. In contrast mice fed the ‘fast food’ diet but with added pro-biotic yoghurt avoided the onset of obesity, despite eating the same ‘fast food’ diet high in fat, sugar and low in vitamins and fibre. The addition of the yoghurt counteracted the pro-inflammatory effects of the poor diet.

In a detailed set of experiments the authors moved from looking at yoghurt to looking at the probiotic bacteria in the yoghurt, particularly a strain of bacteria called Lactobacillus reuteri. Mice fed the bacteria, in water and without the yoghurt, were still protected from the onset of obesity, and that the immune system was a key component of this positive effect.

In this latest paper the authors again use this beneficial probiotic but in this case they look at cancer development in mice. First they compared cancer development in mice fed the ‘fast food’ diet and those fed a more normal mouse diet. And, as you can probably guess, the ‘fast food’ diet was associated with both obesity and a higher incidence of breast cancer than the control diet. No surprise there. But the addition of probiotics to the diet reduced both cancer incidence and the size and growth rate of tumours that did develop. Now here’s where we get the surprise, because why should adding probiotic to the diet and helping the good bacteria in the gut, have an influence on breast cancer development?

The authors took this work a step further and then used mice with a genetic predisposition to breast cancer and fed one set the ‘good’ diet and the other set the ‘good’ diet with the probiotic. Now in these mice even the good diet led to cancer, though of course there was no obesity involved this time. However, and this is why this is such a great piece of news, the mice who also received the probiotic had lower cancer incidence, slower growing tumours and a longer survival time. In other words in spite of their genetic make-up there was a degree of protection from cancer just with the addition of a probiotic.

The papers go into much more detail on the mechanisms at work, principally to do with different classes of cells in the immune system, but that key result really stands out.

There are the usual caveats about extrapolating from mice to humans, but there is some evidence in people that yoghurt consumption can have a protective effect, both in obesity, metabolic syndrome and cancer. The next step is to take this work to another level and to start thinking about clinical trials. There are lots of ways we can test this out. For example, how about a trial in women with high risk of breast cancer recurrence? Or a trial in women with a genetic predisposition to cancer? And what about some work to see whether this protective effect can apply to other cancer types?

And, of course, there is nothing to stop people adding live pro-biotic yoghurt to their diets, or even taking pro-biotic tablets or drinks if they don’t like yoghurt.

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