Wednesday, July 17, 2013

Vegetarian Diets Found To Protect Against Cancer

I have a few comments on this study from the beginning of this year:

Vegetarian Diets And The Incidence Of Cancer In A Low-risk Population, Cancer Epidemiology, Biomarkers & Prevention, February 2013

It says:
1. "Cancer is the second leading cause of death in the United States."
After heart disease, cancer is the leading cause of death in the US. However, it varies depending on a number of factors - age, race, location (exposure to location-related pollution: air, water, soil, radiation), lifestyle (e.g. smoking, drug use, diet, physical activity). Sometimes, cancer is the leading cause of death in a group; sometimes it falls well below things like homicide. (Cancer is the leading cause of cancer in Canada.) So it varies, but the message kernel, that cancer kills a lot of people in the US, isn't negotiable.
2. "Dietary factors account for at least 30% of all cancers in Western countries."
This is nebulous number that has gained undeserved credibility merely for the amount of times it has been repeated - and unchallenged. Dr. Campbell addressed it in his new book, Whole: Rethinking The Science of Nutrition:
"The truth is, it's almost impossible to assign meaningful numbers to the relative contribution of genes and lifestyle [in determining which diseases we get], let alone the specific contribution of nutrition.

This uncertainty became clear to me many years ago when, from 1980 to 1982, I was on a thirteen-member expert committee of the National Academy of Sciences preparing a special report on diet, nutrition, and cancer. ... We were asked to estimate the proportion of cancers caused by diet. ... A report [from 1981] developed for the now-abolished Office of Technology Assessment ... had suggested that 35% of all cancers were preventable by diet.

Our committee's task of creating our own specific estimate of diet-preventable cancers proved to be impossible. ... We also knew that the the previous report ... did not fixate on a precise number for diet-preventable cancers; the 35% cited by the media was a result of sloppy reporting. In fact, the estimates ranged broadly, from 10% to 70%. The seemingly finite figure of 35% ... was suggested as a reasonable midpoint within this range, because a range of 10% to 70% would only confuse the public."
So, diet could account for up to 70% of all cancers, or not, depending on a host of other factors. Not knowing is very different than stating a figure of 30%.
3. "As people do not consume individual foods but rather combinations of them, the assessment of dietary patterns may offer valuable information when determining associations between diet and cancer risk."
Dietary patterns! What did I tell you? Studies designed on a reductionist framework, that seek to determine the effect of a single nutrient, can, while offering insight into mechanisms, fail to deliver a realistic public health message in a world where people eat food, in unique combinations. Reductionist studies also lead to supplementation, which can lead to deficiencies of non-supplemented nutrients, as well as cause outright harm.

4. "Conclusion: Vegetarian diets seem to confer protection against cancer."
The effect was strongest for vegan diets:
"Vegan diet seems to confer lower risk for overall and female-specific cancer than other dietary patterns."
That was the finding of this study of dietary patterns among 69,120 Seventh-day Adventists. Short follow-up: ~4 years. Adventists are a good group to study because their low alcohol consumption and less frequent cigarette smoking reduces confounding by these factors.

This was interesting. Large differences were observed in BMI:
  • Non-vegetarians: 28.6 kg/m2
  • Semi-vegetarians: 27.1 kg/m2
  • Pesco-vegetarians: 26.12 kg/m2
  • Lacto-vegetarians: 25.9 kg/m2
  • Vegans: 24.0 kg/m2

As animal food consumption declined, weight declined. Vegans had the lowest proportion of overweight and obese participants, which was suggested as being responsible for lower incidence of hormone related cancers, such as breast cancer.

What I'm saying here is that, for many people reading this, cancer may be a greater risk than heart disease or stroke, and diet may be the primary controllable factor in preventing it.

No comments: