An Unexpected Link

When most people think of cancer prevention, they think of smoking and the prevention of obesity, with the remaining cancer cases put down to "I don't know", "genetics" or "bad luck". But what about the composition of our intestinal bacteria? These are commonly known to be responsible for prevention of minor respiratory or gastrointestinal infections, but not many know that they may have an effect on something as serious as cancer.

Sauerkraut. Source: Bdubay

Our intestinal bacteria, if at healthy levels, are around 100 trillion in number and live with us in a symbiotic relationship. We give them protection and an assured supply of (indigestible to us!) food; they help us to digest food, aid our immune system and crowd out harmful species. So how does it all go wrong? Infections, antibiotic use and abuse, smoking, aging and diet all affect intestinal bacteria. In fact, epidemiological studies link abdominal infections, antibiotic use and both to colorectal cancer development (at least, when antibiotics aren't followed by probiotics, as sometimes they are necessary). Altering intestinal bacteria has demonstrated influence over both the risk and progression of colorectal cancers, not only in carcinogen-induced models but also in genetic models. This is partly because of by-products of bacterial species: substances that influence tumour development include hydrogen sulphide and the Bacteroides fragilis toxin, while short-chain fatty acids suppress tumours. It doesn't stop here: experimental models of bacteria alteration have shown effects on cancers such as that of the breast and liver. Presumably, this is because of the effects of intestinal bacteria on inflammation and metabolism. In patients who have cancer and are choosing conventional treatment, chemo and radiation are also toxic to our bacteria. This may be harmful, by killing off beneficial species and leaving space for harmful ones to grow...or it could be helpful by killing harmful species and allowing the microbiome to reset. What if this is behind so many cases of long-term survivorship? Anyway, it is best to avoid cancer and its conventional treatments in the first place.

How can we avoid developing harmful compositions of gut bacteria, in order to prevent cancer and other illnesses? Well, many people do not actually do the most effective way to prevent infections that may require antibiotic treatment: washing their hands! In a study from Michigan State University, only 5% of people washed their hands correctly. "Correctly" means to wash your hands for 15-20 seconds, using soap and water. Fifteen percent of men and 7% of women did not wash their hands at all. Half of all men used soap, while just over three-quarters of women did. You can also strengthen your intestinal bacteria, and by extension your immune system, with probiotics or fermented foods. The earliest record of fermentation comes from the Middle East in around 6000 BC, the very dawn of history, and most cultures traditionally include fermented foods in their cuisine. Sometimes, this even makes poisonous plants into nutritious foods. Lacto-fermentation encourages Lactobacillus species of bacteria to develop, which produce the lactic acid (and short-chain fatty acids!) that deters harmful species. However, when you lacto-ferment foods, salt is required to prevent putrefying bacteria. Overall, while our intestinal bacteria composition is integral to our health and protection against cancer, there are quite simple ways of maintaining it that do not necessarily call for expensive supplements.