Some claim that humans are more or less perfectly 'adapted' to consuming animal products, or that we are more 'adapted' to eating an omnivorous diet consisting of eggs, meat and dairy products than we are to eating a vegan diet. Some of these link suggest something else...
Skim Milk / Lo-Fat Milk Linked to Prostate Cancer
Remarkable Cancer Recovery on the Raw Vegan Diet
Cancer: Why We're Losing the War
Who should become vegan: Cancer prevention
Vegan diet 'cuts prostate cancer risk'
Vegan diet and breast cancer risk - Scientific update
Vegan proteins may reduce risk of cancer, obesity, and cardiovascular disease by promoting increased glucagon activity.
Going vegan: Cancer forced a life change.(The Providence Journal)
Very-Low-Fat Vegan Diet May Offer Cancer Protection
Vegan diet taught as cancer deterrent
On Cancer and a Vegetarian Diet
MD Anderson Cancer Center: Complementary Therapies: Vegan Diet
Natural Cancer Cure: Woman Cures Breast Cancer with Vegan Diet
Cooking to combat cancer: the vegan philosophy
The Bristol Approach To Living With Cancer
Vegan Diet may help to reduce cancer
Vegan diet may reverse cancer
Cancer patients go vegan
Cancer: Killing Animals Is Killing Us
Milk, dairy products and cancer risk
A case-control study of diet and the risk of ovarian cancer (eggs, cholesterol)
Milk and lactose intakes and ovarian cancer risk in the Swedish Mammography Cohort
Premenopausal Fat Intake and Risk of Breast Cancer (fat mainly from red meat and high-fat dairy foods)
Dietary Factors and Risk of Colon Cancer in Shanghai, China: diets high in red meat, eggs, and preserved foods increase the risk
Egg consumption and cancer of the colon and rectum
Research Shows Why African-Americans Get More Colon Cancer than Native Africans
Study Suggests High-Meat Diets Encourage “Bad” Bacteria in the Gut
Red Meat May Be Linked to Pancreatic Cancer
Finally, a quote about vegan vs. lacto-vegetarian impact on cancer from www.cancerproject.com
There are also studies finding that there are no associations between eg. breast cancer and animal products or ovarian cancer. So... how do we know which of these studies we can rely on?Steering clear of meat, dairy products, fried foods, and other fatty fare is an important first step in preventing cancer—and in surviving cancer if it has been diagnosed.
From a vegan point of view, the significant part is that even if there may be animal products that eg. in very small amounts aren't harmful in any scientifically proven way, we don't need these animal products, because we can get the nutrients we need from non-animal sources. Even the very fragile vitamin B12, which vegans may have low levels of (mainly due to our modern lifestyles and what could be described as 'environmental reasons') can be compensated for - if necessary - by taking supplements (which often are produced by using a plant based fermentation method).
For a number of years we have all seen general advice about eating more plants, and less meat. Even if there are some studies that "can't find any significant associations" between eggs/meat/dairy products and cancer, and some that do - there is no scientific basis for suggesting that eating more eggs, meat or dairy is needed to cure cancer - or, if animal products have a positive effect, that they are the only solution, because when reading studies that somewhat seem to justify use of animal products (eg. one I saw about eating three eggs a week during adolescence decreasing the risk of breast cancer by 18%), there's often (like in this case) a parenthesis about diets rich in vegetable oils and dietary fiber having similar effects. Or, if a nutrient found in an animal product - like choline - has a good effect on a disease, it is said that this products is good for us, often without mentioning that the same nutrient can be found in plants (in the case of choline: in wheat germ and cauliflower).
On another note, there are different ways to read numbers in such studies. A text like this "a vegetarian diet reduces cancer fatalities by up to forty percent according to many studies including the British Medical Association" will look different from a veg*n perspective. While I doubt that some will claim that 40% isn't that much or that cancer isn't a good marker for what humans are adapted to eat, if we look at the same number from a vegan perspective, adding meat to a vegan diet would then increase the cancer fatalities not by 40%, but by 66,67%. Why? Because 100 minus 40% = 60, but 60 + 40% isn't 100. Going from 60 to 100 is a 66.67% increase. 100 is 166.67% of 60.
The important part is of course not the numbers, but the many reports (not paid by, or performed by vegans) that demonstrate that a diet that doesnotconsist of animal products is much more suitable for humans - in spite of the hundreds of thousands of years of 'adaptation'.
Another example that demonstrates this is that even if most humans for the major part of the recent human history in the Western world may have been eating a small or large amount of animal products, it doesn't take more than a few years to 'lose' that adaption: a vegetarian or vegan who has not been eating meat or dairy for some time will often have trouble digesting even a small amount of such products. It often takes time to 'tune in' to animal products again. An omnivore who haven't had an apple, cucumber or banana for a few years won't normally have any reaction against these plants at all.