Vegetarian Diets And Cancer

If you read the recent headlines such as ‘Being a vegetarian could kill you’  or  ‘Vegetarian diet raises risk of heart disease and cancer’ you couldn’t be blamed for ditching your tofu burger in favour of a bacon sarnie. But the study behind these scarelines compared a vegetarian population in India with a group of American carnivores – not so much comparing apples and oranges as tigers and elephants!

Do vegetarian diets cause cancer?

The research which grabbed all this media attention suggested that following a vegetarian diet may increase the risk of cancer and heart disease by reshaping human DNA to produce mutations. The researchers came to this conclusion after comparing the genes of 234 people from Pune, India, who ‘primarily’ follow a plant-based diet with those of 311 Americans (mostly from Kansas) who follow a traditional, meat-laden Western diet. They found a higher frequency of a particular gene mutation which increases the conversion of plant polyunsaturated fats into an omega-6 called arachidonic acid (AA). This mutation was present in 68% of the people studied in Pune, India, compared with 18% of Americans.

AA is important for healthy cell membranes and is involved in regulating some immune reactions – mostly those involved in the inflammatory response. AA is readily available in a meat-based diet, but can be scarce in a plant-based diet. The researchers therefore suggested that following a vegetarian diet through many generations has favoured those carrying this particular mutation, who were more likely to thrive as a result. Carnivores, however, who get plenty of AA from their diet, don’t need this mutation. In fact, it was suggested they were more likely to thrive without it because inheriting a tendency to generate higher levels of AA would promote inflammation and unwanted blood clotting, both of which are associated with a higher risk of heart disease and cancer.

So far, so good. Sounds plausible, right? It’s hardly a surprise to find genetic differences among populations of different ethnic ancestry living on different continents. But somehow, this story was twisted to claim that following a vegetarian diet long-term increases your risk of cancer. This is a huge conclusion to draw from the genes of a small number of people in Pune, India (who follow a ‘primarily’ vegetarian diet) and a small number of individuals from the United States, two-thirds of whom live in Kansas.

Do people from Pune actually have a higher risk of cancer?

Most studies show that a vegetarian diet is anti-inflammatory rather than pro-inflammatory. A plentiful intake of vitamins, minerals and plant antioxidants more than offsets any tendency to make more AA in those who might have inherited this particular mutation.

So I decided to look at the actual cancer figures for these two areas.

According to the Pune Cancer Registry, the estimated average annual incidence of cancer per 100,000 population was 53.1 for males, and 64.8 for females (figures collected between 2006 and 2010).

According to the Kansas Cancer Registry, the estimated average annual incidence of cancer per 100,000 population was 539.7 for men and 415.3 for women (between 2003 and 2012).

Big difference. It looks like following a ‘primarily’ vegetarian diet in Pune, India, is associated with significantly lower rates of cancer than for adults following a western-style diet in Kansas, United States – irrespective of this particular genetic mutation and all the other risk factors involved such as smoking, pollution, alcohol, obesity and goodness knows what else.

If the Pune population were to stray from their traditional diet with a balanced omega-6 to omega-3 ratio to follow a Western diet with a high ratio of omega-6 to omega-3, all bets are off – which is what the original study actually said. It did NOT say that if you live in the West and eat a vegetarian diet it could kill you!

To draw any valid conclusions along those lines, you would have to compare similar populations from the same region, rather than different ethnic populations from different continents. And that’s exactly what another recent study did by comparing mortality in vegetarians and comparable non-vegetarians in the United Kingdom.

Following a plant-based diet does not increase your mortality

Data was collected throughout the UK from 60,310 people, aged 20 to 89 years, of whom 18,431 ate meat at least five times a week, 13,039 ate meat less-frequently, 8,516 ate fish but not meat, and 20,324 were vegetarians, of whom 2228 were vegan and avoided all animal-based foods.

Each person was followed for up to 15 years or more (a total of 1 million years combined!) to see if their diet group had changed, and to record the causes of any deaths.

There were no significant differences in the total number of deaths, from any cause, between the diet groups. Vegetarians were not more likely to die. In fact, those who had a low intake of meat, fish eaters and vegetarians were 7% less likely to die during the follow-up period than regular meat eaters, although this was not statistically significant.

And when causes of death were broken down, vegetarians and vegans were significantly less likely to die from pancreatic cancer and digestive diseases than regular meat eaters, and fish eaters were less likely to die from colorectal cancer than regular meat eaters

A recent study involving American women found no differences in breast cancer risk between vegetarians and non-vegetarians, although a lower risk in vegans was ‘possible’.

A study from The Netherlands concluded that vegetarians, fish eaters and people who ate meat on just one day per week had the same risk of developing lung cancer, postmenopausal breast or prostate cancer as people who ate meat on a daily basis.

And, when all the data from 96 studies was crunched, it was concluded that people following a vegetarian diet were 8% less likely to develop any cancer than omnivores, while following a vegan diet was associated with a 15% lower risk of total cancer.

I could go on, but I’m in danger of becoming boring. Repeat after me: FOLLOWING A VEGETARIAN DIET DOES NOT CAUSE CANCER – despite what the recent headlines tried to tell you.

I had a veggie day yesterday, so I’m off to eat one of my hubby’s delicious, home-made  Cornish pasties, made from Angus beef! The evidence that red meat causes cancer is just as spurious.

What did you make of these headlines? Did they make you think twice about your chosen way of eating? Do mangled headlines that misinterpret study findings make you cross, too?

Image credits: victoria KH / shutterstock

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Dr Sarah Brewer
QUORA EXPERT - TOP WRITER 2018 Dr Sarah Brewer MSc (Nutr Med), MA (Cantab), MB, BChir, RNutr, MBANT, CNHC Cert IoD qualified from Cambridge University with degrees in Natural Sciences, Medicine and Surgery. After working in general practice, she gained a master's degree in nutritional medicine from the University of Surrey. Sarah is a registered Medical Doctor, a registered Nutritionist and a registered Nutritional Therapist. She is an award winning author of over 70 popular self-help books and a columnist for Prima magazine.

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