(Photo courtesy of Raven3K)
Well, we are already aware of this, mostly from population studies, but a recent study involving close to 62,000 adult participants (about half of whom are classified as vegetarian) found that that vegetarians developed less cancer -- specifically of the blood, bladder, skin, and stomach.
The study, which is published in the British Journal of Cancer, divided the people into three groups: meat eaters, those who ate fish but no meat ("pescatarians"), and vegetarians.
Given that eggs and dairy products are not protective against cancer (and might raise the risk), the findings make quite a powerful statement for the exclusion of meat, which is, at the end of the day, the only thing that separated the meat eaters from the vegetarians. Note that fish consumption did NOT offer cancer prevention benefits over its avoidance in this study. I would love to know the rates of cancer among vegans; this was not measured.
One of the big challenges with doing this sort of comparison study is that it is not really that descriptive to label oneself as a "vegetarian" or "meat-eater" because the latter could indeed consume more fruits and vegetables than the former.
Picture two groups of people: one that at a completely vegan diet, and one that ate a meat-containing one. But here is how they eat:
Breakfast: Oatmeal with walnuts, flax, dates, and strawberries
Lunch: Big green salad with olive oil/balsamic, whole grain crackers, and a cup of low-fat yogurt
Snack: Fresh fruit
Dinner: Stir fry with onions, broccoli, carrots, sliced almonds, and shrimp, with brown rice
Breakfast: New York-style salt bagel with soy margarine, coffee with sugar and nondairy creamer
Lunch: Soy turkey sandwich on white with Spicy Sweet Chili Doritos (yup, they're vegan)
Snack: Vegan chocolate chip cookies
Dinner: White pasta with marinara, chicken-style gluten strips, iceberg lettuce salad with Kraft creamy Italian (yup, it's vegan)
Obviously this is an exaggeration, but I hope I've made my point. Which group do you think is better protected from cancer? It's very difficult to study the health benefits of an eating style that can take on so many different varieties regarding healthfulness of its constituents.
What we really need to see is the RELATIVE IMPACT of both meat avoidance AND fruit/vegetable inclusion, to really demonstrate the powerful benefits of a healthful vegan diet based on whole plant foods.