Does A Vegetarian Diet Prevent Cancer?

A few days ago, Clearthought blogger Blacktag (When docs turn gods) engaged in a discussion about the health benefits of a vegetarian diet at Mr. Wang's blog article entitled "Vegetables Will Save The World".

The relevant exchange in the comments section is reproduced here for your reading pleasure.

Mr Wang Says So said:

The problem with red meat is that it has some strong links with quite a variety of cancers including breast cancer, colorectal cancer, stomach cancer, lymphoma cancer, bladder cancer and prostate cancer. And of course, since red meat has a high content of saturated fat, it is associated with cardiovascular diseases.

So you see quite quickly that red meat is a risk factor for just about all the top killer diseases in your average modern society (except lung cancer & COPD).

The other problem with meat in general is that it has synthetic growth hormones in it. Basically all the cows are jabbed with chemicals to make them grow faster.

The EU has banned the use of such hormones by the agricultural industry, but I think it goes on elsewhere.


RICHARD SEAH said:

Three cheers for this post. I am certainly encouraged to see regular "socio-political" bloggers like Mr Wang venture into the topic of health and highlight the harm of meat and milk.

But ah! Did you read the Doc Talk column by Singapore's "leading" oncologist Dr Ang Peng Tiam in Mind Your Body June 4?

According to him, all these beliefs about meat, milk and sugar contributing to cancer are "old wives tales".

So that makes you, Mr Wang, an "old wife" as well, along with all the scientists whose research you cited.

Such is the sad state of affairs in Singapore that even lawyers and bloggers like Mr Wang are more enlightened on health issues that top cancer doctors.


Blacktag said:

From a previous commenter: "Such is the sad state of affairs in Singapore that even lawyers and bloggers like Mr Wang are more enlightened on health issues that top cancer doctors."

My take: now I'd probably go look for Mr Wang for good advice on blogging, or perhaps the law, but advice on cancer? Sure, Mr. Wang could be right, but chances are, he is probably wrong, and none of us have time for this.

No one ever talks about the link between natural carcinogens found in our daily foods (including organic vegetables) and cancers, since it's inconvenient and unprofitable to the organic food industry. Though few of its carefully crafted evangelists would listen anyway.

Just to add, there are very good reasons for adding preservatives to food for example. I think it began with rotten food in transit.

Haven't we all heard enough stories about the person who was vegetarian, avoided smoking and other bad habits, but still wound up with cancer or heart disease or whatever? What does that suggest to one that is statistically inclined?

Here's some advice others might find truthful (but perhaps mildly depressing, given that it reminds us how helpless we really are).

1. Colorectal cancer: best quality evidence indicates that a high fruit and vegetable diet does not prevent polyps or colorectal cancer.

2. Breast cancer: All major intervention studies to date in ordinary people and breast cancer survivors suggest a diet high in fruits, vegetables and low in fat make no difference as to breast cancer incidence.

3. Lymphoma, Stomach, Bladder, Prostate: no need to even Google the answer.

Here's the only health advice that will be useful on a broad basis for most people, well supported by good data, but so highly unprofitable for industry that you'll hardly hear much about the message:

(a) Stop smoking.
(b) Exercise regularly.
(c) Eat less.

Meat is fine. Food with preservatives is as healthy as organic food really, save your money for a balanced diet. It's the total number of calories that matter.


Celestial said:

dear blacktag, there are more than just preservatives found in processed or even the so-called natural food.

Vegetables can be bad as well because of GMO, pesticides..etc

At the end of the day, we are eating our own "Karma".

Nevertheless, i support veg diet.


Mr Wang Says So said:

I found an interesting link:

http://www.hsph.harvard.edu/nutritionsource

The site is by a highly reputable institution (Harvard School of Public Health); it accepts no advertising or commercial sponsorship; nor does it endorse any particular products.

I think it is therefore a good source of independent, unbiased and expert info on healthy nutrition.

Interested readers are invited to check out the site and see for themselves.

Consider my post and comments again, then go there and see what it says about red meat, fruits, vegetables etc.


Blacktag said:

Thank you Mr. Wang for that link to the Harvard School of Public Health, which in fact, eerily echoes my sad looking three point plan exactly. Since we all like orang putih quotes, I shall draw some quotes (within context, I assure you) from the site:

"Aside from not smoking, the most important determinants of good health are what we eat and how active we are."

Sounds familiar ?

Some Singaporean dispensed free advice yesterday:
(a) Stop Smoking.
(b) Exercise more.
(c) Eat less.

"Most important of all is keeping calories in check, so you can avoid weight gain, which makes exercise a key partner to a healthy diet."

Thank goodness for medical school, it allows me to echo the Americans, with half the respect.

Now let's have some perspective.

No one likes being told to stop smoking, exercise and eat less (even though these are the only three solidly demonstrated interventions). And that would lead to a very sad looking website, instead of a colourful one, full of pretty fruits and vegetables.

The reality is that the three recommendations I have made are supported by Level I evidence. (a randomized controlled trial).

The fruit / vegetable hypothesis is no more than Level III (case control/ cohort studies), and all attempts to elevate this to Level I by formal large trials have failed, suggesting that the whole truth is not there, and that the cohort studies are not telling the whole truth. Does a lack of level I evidence mean it is untrue? Certainly not, but since formal trials have not shown protective effects, we can say that there is good evidence that there is no direct protective effect. Alternative hypotheses (no more than hypotheses) may include

(a) that the ang-mohs are not eating the sorts of vegetables that wise Chinese nutritionists want them to eat, resulting in the wrong sort of outcome.
(b) there is a confounder. It may be possible that consumption of fruits and vegetables is linked to increasing disposable income. Given that lifestyle factors are very different between those with/without disposable income, one of these (rather than fruit/vegetables) may underpin the difference in cancer incidence.


Anonymous said:

Blacktag, it seems that your biggest point is that it's important to exercise regularly, not smoke and not overeat. However, these are rather obvious and well-known facts, hardly the sort of thing that one needs to go to medical school to learn. And I would add , hardly the sort of thing that Mr Wang would bother to mention on his blog.

If you really want to contribute usefully, you could perhaps comment on the relationship between meat; saturated fat; harmful cholesterol and high blood pressure, stroke and heart disease.

Or you could tell us more about your Levels I, II and III and explain, for example, whether it is your view that the public should disregard all health studies that only hold true at Levels 2 and 3.

Also, I haven't bothered to visit that Harvard website, but I would have imagined that if you had wanted to copy some excerpts, the excerpts relevant to the present discussion would be those specifically relating to red meat, fruits and veggies. Rather than some general statement about not smoking or not exercising enough etc. Why don't you choose some more-salient excerpts to explain whatever point (whether positive or negative) that you want to make about vegetarian diets (if you do have any such point).


Blacktag said:

This will be my last comment, and I thought I should be constructive and provide useful health advice for readers here. Warning: this is a long comment.

[stopping smoking, exercising and eating less] are rather obvious and well-known facts, hardly the sort of thing that one needs to go to medical school to learn.

You'd be very surprised. Unfortunately, there are people less perceptive than yourself who don't realize that. These individuals find popping pills/supplements, taking herbs and drinking diet sodas a more proactive act of control than stopping smoking.

Generally, the impact of any of the three interventions prescribed far outweighs any other intervention out there in terms of actual health outcomes, which indeed distract from these core issues. There is really very little benefit to changing to a vegetarian diet, and maintaining the same caloric intake. Perspective is the issue. The best analogy is a person who orders a supersize meal with a diet coke.

The major problem in all these nutritional recommendations derived from epidemiological studies (that often conflict) is that the noise generated by industry and well meaning individuals detract from the actually useful three point recommendations. For example, the simple fact that a low fat diet makes no difference to weight loss versus a high fat one with the same caloric intake. is still little known today.

"If you really want to contribute usefully, you could perhaps comment on the relationship between meat; saturated fat; harmful cholesterol and high blood pressure, stroke and heart disease."

I define my own usefulness by the dispelling of myths, and the provision of truth, not hearsay. Mr. Wang began from "red meat is a risk factor for just about all the top killer diseases" and arrived at the conclusion that a vegetarian diet was the answer. Now I may agree that red meat is regarded as a probable risk factor for colorectal cancer (but not other cancers) based on best Level III evidence currently, but the conclusion that a vegetarian diet is better for you does not follow. There are lots of in betweens, including limiting of red meat, as well as white meat. In fact, the difference between red and white meat has not been highlighted in these comments to date.

Or you could tell us more about your Levels I, II and III and explain, for example, whether it is your view that the public should disregard all health studies that only hold true at Levels 2 and 3.

Absence of gold standard evidence does not mean a need to reject a supposition in public health. So where it is not formally examined, it may be possible to accept lower level evidence. However, in the presence of higher level (i.e. better) evidence, it is irrational to deny the findings of randomized trials. As mentioned, very large randomized trials demonstrate that diets rich in vegetables and fruits do not protect against breast cancer or colon cancer, despite suggestive Level III evidence.

The link between colorectal cancer and red meat is based on Level III evidence, which is quite extensive. There is no Level I evidence, because it is not possible to do a formal trial in randomizing people to eating more / less red meat, so we should accept this link. The link between red meat and other cancers is not established.

Also, I haven't bothered to visit that Harvard website
...

Then may I assure you that nowhere in the Harvard website does it say a vegetarian diet is good for you, and allow you to verify this?

These would be my answers today, to a patient's questions:

Is consumption of red meat linked to higher incidence of cancer overall?
Yes there is suggestive data for colorectal cancer, but not conclusive evidence for other sorts of cancer.

Is consumption of white meat linked to higher incidence of cancer?
No, there is no convincing data.

Is it therefore prudent to limit consumption of red meat then, to prevent colorectal cancer?
Yes, but don't get distracted from the bigger issues, which are (a) stop smoking (b) exercise and (c) lose weight, all three which are far more strongly linked to prevention of almost ALL cancers than mere red meat avoidance. Having said that, prudence and limitation of consumption should be applied to all food groups. There is relatively little benefit being vegetarian and maintaining the same caloric intake.

Can I still get cancer if I avoid red meat completely?
Certainly, the link between red meat and other sorts of cancers is not definitive based on current data. The incremental benefit in preventing colorectal cancer by avoiding red meat may be outweighed by other risks, some modifiable (smoking and obesity) and some not (e.g. age and family history).

One has to keep in mind that at the end of the day, these findings are derived from large population studies, which apply to the general group, rather than the individual. Hence the large proportion of people who develop cancers, despite not having specific risk factors.

Based on current knowledge, does that mean one has to be vegetarian for potential gains in life expectancy / cancer prevention from this?
There is no good data to support this. Options include limiting red meat intake, as well as taking white meat such as fish and chicken.

Dear Mr. Wang - I hope this is clear and sufficiently constructive health advice for the readers, and that some people will stop smoking and start exercising. :) The latter is truly the only miracle panacea currently known.