NPR ran an article today, Fruits and Veggies Prevent Cancer? Not So Much, It Turns Out…

Excerpts:

“A huge nine-year study of diet and cancer, involving nearly a half-million Europeans in 10 countries, finds only a very weak association between intake of fruits and vegetables and cancer incidence. The study is in the current issue of the Journal of the National Cancer Institute. Those who get an extra two servings of fruits and veggies a day lower their cancer risk by only four percent.”

Not the best news, but at least it cuts the risk by 4%. I’m inclined to think this study is correct, that fruits and vegetables help prevent cancer, but not by a lot. Good news is later in the article:

“But meanwhile, there’s a pretty strong reason for everybody to continue eating lots of fruits and vegetables. It’s called cardiovascular disease. A 2004 study in the JNCI found that eating five servings of fruits and vegetables a day is associated with a 28 percent lower risk of heart disease and stroke, compared to people who eat fewer than 1.5 servings a day.”

I just updated Another Internet Soy Article with the following:

A 2009 report from the Shanghai Breast Cancer Survival Study showed that women with a prior diagnosis of breast cancer (including estrogen-positive), who ate more soy, had lower rates of death and cancer recurrence (12). The study followed women for an average of 3.9 years after a diagnosis of breast cancer. The researchers measured a beneficial effect of up to 11 grams of soy protein per day. Table 3 shows the results.

12. Shu XO, Zheng Y, Cai H, Gu K, Chen Z, Zheng W, Lu W. Soy food intake and breast cancer survival. JAMA. 2009 Dec 9;302(22):2437-43.

I always find it amusing when I’m reading nutrition propaganda from someone using outdated information and they say something like, “As far back as [date], we knew that…” And so it disappoints me to have to do the same thing right now: As far back as June, we knew that vegetarians had a lower cancer rate than regular meat-eaters; it’s just that it’s taken me until now to update VeganHealth.org and post about it.

And, why am I saying “regular meat-eaters” rather than just “meat-eaters”? Because, in this report from EPIC-Oxford (1), the people who ate no meat other than fish had an even lower cancer rate than the vegetarians, in comparison to the regular meat-eaters. Here are the rates as compared to regular meat-eaters:

Vegetarians .88 (.81, .96)
Fish-eaters .82 (.73, .93)

Now before anyone says that fish-eaters, therefore, had a lower cancer rate than the vegetarians, let me point out that a cursory glance at those confidence intervals indicates to me that there would not be a statistically significant difference if you compared the vegetarians to the fish-eaters; but the study did not report testing for that.

When breaking the cancers down into categories, in comparison to the regular meat-eaters, the vegetarians had lower rates of stomach (.36, .16-.78), bladder (.47, .25-.89), and lympthatic & hematopoietic tissue (.55, .39-.78) cancer. They had a higher rate of cervical cancer (2.08, 1.05-4.12).

In comparison to the regular meat-eaters, the fish-eaters had lower rates of colorectal (.77, .53-1.13), prostate (.57, .33-.99), and ovarian (.37, .18-.77) cancer. They didn’t have a higher rate of any cancer.

So, can we now say that vegetarians have a lower rate of cancer than meat-eaters? Well, fish-eaters are meat-eaters, so that might be kind of hard. We could say that vegetarians have a lower rate of cancer than chicken eaters.

To see more of the numbers and details, as well as results from other studies on vegetarians and cancer rates, click here.

Footnote

1. Key TJ, Appleby PN, Spencer EA, Travis RC, Allen NE, Thorogood M, Mann JI. Cancer incidence in British vegetarians. Br J Cancer. 2009 Jul 7;101(1):192-7. Epub 2009 Jun 16.

I just updated Another Internet Soy Article on VeganHealth.org with information on breast cancer. Link. It’s too much to reprint here but it is all good news, with decent evidence that eating soy in moderate amounts can actually decrease the risk of breast cancer. I wouldn’t go so far as to claim that we know it does, but at the very least we can conclude that it doesn’t increase the risk for breast cancer.

Medscape published a very interesting, short article yesterday, Diet, Nutrition, and Cancer — Don’t Trust Any Single Study. It is mostly an interview with Walter Willet, MD, DrPH, from the department of nutrition at Harvard School of Public Health. Among the topics covered are charred meat and the link between alcohol and breast cancer.

Unfortunately, you have to register in order to read it, but I think it’s worth it for anyone who is interested in this subject.

(Thanks, Maynard.)

Many people commented on yesterday’s post, Cancer and Vegetarianism, saying they wished the researchers had separated vegans from vegetarians.

In the paper, the authors stated, “…because of the small number of cancers among vegans, in this article the vegans are included in the vegetarian category.”

All we really know from that statement is that vegans didn’t have an unusually large number of cancers – so much that they would have reached some sort of statistical significance. It could also be that vegans have less cancer, or even a lot less cancer, but there was not enough data to create any sort of statistical significance.

I think it’s reasonable to hold out some hope that vegans will eventually be shown to have less cancer than meat-eaters or lacto-ovo vegetarians.

It could also be that except for in cases of very high amounts of animal products and very low amounts of fruits and vegetables, diet might not affect cancer that much. In the more moderate amounts of these foods, your body may be getting enough antioxidants, or have enough other mechanisms, to deal with carcinogens introduced by food.

I didn’t include a citation to the study in the original post:

Key TJ, Appleby PN, Spencer EA, Travis RC, Roddam AW, Allen NE. Cancer incidence in vegetarians: results from the European Prospective Investigation into Cancer and Nutrition (EPIC-Oxford). Am J Clin Nutr 2009;89(suppl):1S-7S.

Comments

In case you aren’t aware, you can comment on the posts (by clicking on the “View Article” at the bottom of each post). You can also subscribe to the Comments for individual blog posts.

On March 11, a study was released that measured the cancer incidence among British vegetarians. The study was part of European Prospective Investigation into Cancer and Nutrition–Oxford (EPIC-Oxford). I have updated the VeganHealth.org article Cancer, Vegetarianism, and Diet with the new findings.

(For this article to make sense you should take a minute to read this quick explanation of disease rate statistics if you are not already familiar with them.)

The participants in EPIC-Oxford were recruited from 1993 to 1999 and were followed through 2005. Previously, they had their overall cancer mortality through 2002 reported: Vegetarians had an 11% higher rate of death from cancer, but it was not statistically significant (1.11, .82 – 1.51).

The new findings reported the rates in two different ways:

1. Comparing vegetarians (including vegans) to all the meat-eaters.

2. Breaking the meat-eaters into two groups: regular and fish-eaters (no meat except fish).

The only statistically significant findings were:

• Vegetarians had higher rates of colorectal cancer than all meat-eaters (1.49, 1.09-2.03).
• Vegetarians had higher rates of colorectal cancer than the regular meat-eaters (1.39, 1.01-1.91).
• Fish-eaters had lower rates of all cancer than regular meat-eaters (.83, .71-.96).
• Vegetarians had borderline-significant, lower rates of all cancer than regular meat-eaters (.89, .80-1.00).

Rates for breast, prostate, lung, and ovarian cancer did not differ between groups.

When comparing this study population (including vegetarians and all meat eaters), their cancer rates were 28% lower than the overall population, their smoking rates were about half, and the meat-eating among the meat-eaters was “only moderate.” The authors hypothesized that, “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." Although we consider cancer rates of 1.49 (1.09-2.03) and .83 (.71-.96) as being statistically significant, I'm starting to wonder how relevant measurements of this magnitude actually are. The studies on vegetarians that have shown statistical significance are pretty inconsistent, and most studies have not found statistical significance. On the other hand, if you look at how the smoking rates affected lung cancer in this study, heavy smokers had 87 times the amount of lung cancer (87.3, 37.8 – 202). Now that is statistical significance. Even light smokers (27.1, 11.1-66.4) and former smokers (6.54, 2.89-14.8) had many times the rates of lung cancer as nonsmokers.

If we include these latest findings of vegetarian cancer rates with the others that have been measured (listed in Cancer, Vegetarianism, and Diet), I think we start to get a fairly consistent picture:

Among vegetarians and people who eat moderate amounts of meat and don’t smoke, cancer rates are about the same, but lower than for people who do smoke and eat large amounts of meat. In other words, you can reduce your risk of cancer by not smoking, by limiting meat to moderate amounts (or abstaining entirely), and by eating plenty of fruits and vegetables. The evidence for stronger claims doesn’t seem to be there.

Similarly, the combined colon cancer rates to date seems to indicate that, in comparison to eating moderate amounts of meat, being vegetarian neither increases nor decreases your risk of colon cancer.