The Daily Mail came out with a pretty outrageous headline today, claiming that a “vegetarian diet raises risk of heart disease and cancer.”
So is this statement true?
Not really. The headline is exceptionally misleading. It makes it sound like eating a vegetarian diet increases one’s absolute risk of cancer relative to eating a Standard American Diet (SAD), which is absolutely not the case.
In a new study published in the journal Molecular Biology and Evolution, researchers compared a primarily vegetarian population from Pune, India to a traditional meat-eating American population, mostly from Kansas. The researchers found a higher frequency of the mutation called “rs66698963” in the Indian population.
This mutation helps people convert plant fatty acids into important nutrients, including omega-6 arachidonic acid. Arachidonic acid is important for muscle growth and healthy neurological function in humans and is usually contained in meat, eggs and dairy.
However, arachidonic acid is also known for its pro-inflammatory and pro-blood clotting properties. Today, this genetic mutation can be a problem because omega-6 fats are readily available in an increasing number of foods and oils. Consequently, people with this mutation are retaining higher levels of arachidonic acid in their blood and tissues.
So, it’s fair to say that eating a long term vegetarian diet may cause a greater expression of genes that convert plant oils into arachidonic acid (or it might be inherited). This in and of itself does not raise cancer risk. In fact, if we look at cancer rates in countries like India, where meat consumption is 25 times lower than in the US, we can see they also have cancer rates that are 20 times lower than the US.
To quote NutritionFacts:
For example, “overall cancer rates are much lower in India than in western countries.” U.S. men get 23 times more prostate cancer than men in India. Americans get between 8 and 14 times the rate of melanoma, 10 to 11 times more colorectal cancer, 9 times more endometrial cancer, 7 to 17 times more lung cancer, 7 to 8 times more bladder cancer, 5 times more breast cancer, and 9 to 12 times more kidney cancer. This is not mere 5, 10, or 20 percent more, but 5, 10, or 20 times more. Hundreds of percent more breast cancer, thousands of percent more prostate cancer—differences even greater than some of those found in the China Study.
The study’s lead author, Tom Brenna from Cornell University, notes that it’s not the gene expression that raises the risk, but rather it’s the combination of having that particular gene expression combined with a high intake of Omega 6 fat from refined seed oils. To quote Brenna:
Persons with one of the genotypes that we call the I/I genotype, have on average higher omega-6 arachidonic acid levels, probably because of increased synthesis from plant fatty acids. The I/I genotype is favored in traditional vegetarian populations.
The plant omega-6 linoleic acid – from which the arachidonic acid is derived – is normally at low levels in traditional whole food diets as well as in fruit oils such as olive oil and avocado oil, or in dairy fat. However, it is a factor of 10 or more higher in industrially produced oilseeds such as traditional sunflower, safflower, corn, soy and peanut oils. The increasing availability of high omega-6 seed oils in the developing world will be most pro-inflammatory and pro-clotting for those persons with the genetics of traditional vegetarians because their genotype will maintain higher omega-6 arachidonic acid in their blood and tissues.
Omega-6 arachidonic acid also suppresses omega-3 docosahexaenoic acid needed for brain development starting in pregnancy and through 20 years of age. These are major issues as the fat content of the diet for well-nourished persons is from 15 percent to 45 percent of calories and much of this is cooking and salad oil.
In the U.S., the situation is different. The U.S. oilseed industry is now shifting production of the oilseeds I mentioned, sunflower, safflower, corn, soy and peanut, to high oleic varieties that have similar omega-6 linoleic acid composition as the fruit oils I mentioned, olive and avocado oil, and milkfat as well. As that shift continues, the effects are expected to become less pronounced. My sense is that it is of the utmost importance to introduce these high oleic oils into traditional vegetarian populations.
So what this finding actually translates into is that people who eat a vegetarian diet should eliminate refined plant oils that are high in Omega 6, which is the real risk factor here, not the vegetarian diet. Of course, a headline that says “New study finds vegetarians who consume high amounts of refined oils are at a greater risk of cancer” isn’t exactly clickbait material.
The DM article also makes a few other misleading statements saying, “previous studies which found that vegetarians were up to 40 per cent more likely to develop bowel cancer than those who eat meat.” First off, it’s not “studies” in the plural, it was a single prospective study. Here’s what the study’s authors had to say about that peculiar finding:
Our observation that the incidence of colorectal cancer is higher among vegetarians than among meat eaters in the EPIC-Oxford study is surprising; this difference might be partly due to chance and speculatively might be related to other dietary differences between the groups…
This is a study of comparisons, and the results depend on the comparison group. In the comparisons within the cohort, the vegetarians were compared with all nonvegetarians or with meat eaters. Meat intake among the meat eaters was only moderate, with median intakes of 78.1 g/d in men and 69.7 g/d in women [average US intake is 125 g/d]; these intakes are much lower than those reported in the National Diet and Nutrition Survey for the United Kingdom (19). Consumption of vegetables and fruit was higher among vegetarians than among nonvegetarians, but the differences were not large (,20%). Thus, if high intakes of meat had an adverse effect and high intakes of fruit and vegetables had a beneficial effect, the relatively low meat intake and high fruit and vegetable intake of the nonvegetarians in this cohort could reduce the chance of observing lower cancer rates in the vegetarians than in the nonvegetarians. Furthermore, the results may be influenced by residual confounding because of measurement error in the assessment of confounding factors, and by confounding by unknown factors.
The study’s authors also note that several other large scale epidemiological studies found a significantly lower risk of colorectal cancer among vegetarian populations, and that red and processed meat have convincing evidence that they play a role in colorectal cancer.
And just for good measure, the DM had to throw in this little tidbit of nonsense, “Vegetarians are often found to be deficient in protein, iron, vitamin D, vitamin B12 and calcium, with one study showing that vegetarians had a five per cent lower bone-mineral density than those who eat meat.”
No study in the history of science has ever found that vegetarians suffer from protein deficiency. In fact, dietary protein deficiency isn’t even a clinical diagnosis. There’s never been a single recorded incident of a person suffering from a dietary induced protein deficiency in the history of medicine. Further, high iron intakes are associated with an increased risk of cancer. D and B12 don’t come from animal products. And high dietary calcium intake has virtually no effect on bone mineral density! Further, vegetarians have average intakes of dairy products, so what does that finding say about dairy?! – IT’S NOT GOOD FOR YOU!