Organic food and cancer risk - gut microbe expert on latest research
Tim Spector, King's College London
Organic food is an over-hyped and overpriced fad, according to many people. But a recently published study which followed nearly 69,000 French people over four and a half years seems to indicate there is a link between eating organic foods and a lower cancer risk.
The study found the regular eaters of 16 types of organic products were protected against several cancers by about a quarter. The foods included fruit, vegetables, bread, flour, eggs, meat and cereals.
More than 20% of EU land is now allocated for organic farming and the organic sector is booming. But until now there has been no clear consensus on whether eating organic food is worth the extra cost. So is it time to throw out all your fruit and veg and only shop organic in the future?
Going organic
The study suggests people who regularly eat organic plant foods have a reduction in risk of common cancers. The data also shows a reduction for breast cancer after the menopause – but not before.
But while these results suggest a relationship, it is a long way from proof. This is because the study itself was too short and has the usual biases of observational designs – in that people who are healthier are more likely to eat healthier foods. And while the authors adjusted for body weight, social class and educational level, as well as other differences, and still found a consistent effect, the possibility of bias still remains on any single observational study.
The results, however are most convincing for a reduction in cancer of the immune system called Non-Hodgkin’s lymphoma. This is because two previous studies (also longitudinal and observational) – the largest being a study of 680,000 women over nine years – also showed the same preventive effects. The fact that all three studies show a reduction of risk for this type of cancer (by chance or bias alone) is more indicative that there could be a link between organic eating and a lower cancer risk.
Herbicides and health
There is no hard evidence that the taste or nutrient differences (fibre, vitamins and minerals) of organic vegetables are very different to regular varieties – although analysis suggests they contain more polyphenols. These are compounds that often give plants their colour and provide antioxidant defences and are generally beneficial for human health.
In the US and Europe, fruits and vegetables are regularly sprayed with a range of pesticides and herbicides. Organic plants do still have detectable levels of herbicides and pesticides, but they are five times lower than non-organic products. Many common fruits and cereals such as oats often have high levels – which aren’t reduced much by washing or peeling.
Read more: A controversial weedkiller has won a new five-year lease in Europe, but citizens are fighting back
So it could well be that ingesting chemically treated plants over years may actually increase some cancers. A US jury, for example, recently awarded millions of dollars in damages to a groundsman with Non-Hodgkin’s lymphoma who regularly used the weed killer Glyphosate (Roundup). This weedkiller is widely used around the world and in more than five million acres of farmland in the UK alone.
The government and the EU maintains that these chemicals are safe for humans at doses found in food. But the safety thresholds are based on old-fashioned lab animal data – where rodents are given doses a thousand times higher and see if they develop extra cancers. The safety tests for foods and chemicals have not changed for decades and do not include the long-term effects, for example, on our gut microbiomes.
A gut issue
We have 100 trillion microbes in our lower intestines that make up a community that are crucial for the immune system and for the body’s response to cancer and cancer therapies – such as immunotherapy for melanoma. These microbes and their genes are much more sensitive to chemicals than we are, and this can lead to disruption in their metabolism and the chemicals they produce.
This new knowledge of the importance of a healthy gut microbiome casts doubt on official advice that all pesticides and herbicides are safe for us over long periods of time. And greater scrutiny of the safety of these widely used chemicals in our foods needs to be carried out in well-funded clinical trials – over years, not weeks.
There may of course be no direct effects on humans. But, as yet, no one has provided evidence to show that such chemicals are not harmful long-term for our immune system. So, while the risks for individuals are likely to be low, until we know for sure, for those who like eating lots of plants, spending a bit more for organic fruit and veg (and porridge oats) may be a price worth paying to keep your gut microbes healthy.
Read more: How sauerkraut is leading a food revolution 
Tim Spector, Professor of Genetic Epidemiology, King's College London
This article is republished from The Conversation under a Creative Commons license. Read the original article.
