There are three separate factors which contribute to causing cancer – heredity (by far the least important factor), environmental pollution and diet. A poor diet is second only to smoking as one of the largest preventable risk factors for cancer. The Department of Health estimates that such a diet may be responsible for up to one-third of all cancer deaths (143). Dr Michael Greger, writer and presenter of Stopping Cancer Before It Starts, estimates that 70 per cent of cancers could be prevented by diet (146).

Figures which illustrate how diet is crucial are those for colon cancer. Americans are four times more likely to develop it than Japanese. But when researchers looked at Japanese people who had moved to the US they found that their risk of colon cancer shot up to near that of Americans. The main difference between the two groups was identified as diet – a traditional Japanese diet being low in animal products while a typical US diet was extremely high in them. Japanese Americans tended to adopt the US style of eating once they moved to that country (42).

It is now known that people who eat two or more portions of red meat a day increase their risk of bowel cancer by one-third. And researchers have discovered the mechanism. Published in Cancer Research in 2006, this study took cells from meat eaters and vegetarians and found those eating red meat had a higher rate of DNA mutation, increasing the likelihood of cancer. It seems this damage is caused by N-nitrosocompounds, which form in the large bowel after eating red meat (148).

Another scientific method of looking at diseases such as cancer is to establish how different foods affect them, both good and bad – those foods that may cause the disease (positive) and those that may prevent it (negative). They’re called correlation studies.

One of these studies looked at 37 countries and established a strong positive link between meat and meat protein and intestinal cancer while vegetable protein was negative – it provided protection (43). Another correlation study carried out in Israel followed the growth of the population from 1.17 million to 3.5 million. Over this period, meat consumption increased dramatically by over 400 per cent and cancers doubled (44).

Two other studies, one of breast cancer and one of cancer of the uterus, found similar links between animal protein and fat and cancers. When complex carbohydrates – starchy vegetable foods – were considered, the result was negative (protective) (45, 46). In 1981, a massive study looked at cancer in 41 different countries and found that diets based on beans, maize and, to some degree, rice were good at preventing both breast and colon cancer while meat promoted both (47).

In 1990, the diets of 88,000 women were examined and it became clear that those who eat beef, pork or lamb as a main dish every day are two-and-a-half times more likely to develop colon cancer than those who eat meat only once a month (48). In 1994 came the Oxford Vegetarian Study (see page 6) and its conclusion that vegetarians have a 40 per cent less chance of dying from cancer than do meat eaters. There are many other studies that show vegetarians are less at risk (49, 50) by between 25 and 50 per cent. The ADA and BMA have both found that vegetarians are less likely to develop some cancers.
Interestingly, other studies have found that eating increased amounts of fruit and vegetables contributes to vegetarians’ better chances but doesn’t fully account for it. In other words, there appears to be something in meat which actually appears to cause cancer (51, 52).

The WHO has produced a list of dietary pluses and minuses which affect cancer. Fat, it says, plays a part in breast, colon, prostate and rectum cancer while fruit and vegetables offer protection from lung, colon, bladder, rectum, oral cavity, stomach, cervix and oesophagus cancers. On breast cancer it says there is a direct association between the numbers who die and the intake of high quantities of calories and dietary fats such as milk and beef. This has been confirmed by two very recent studies which have found that breast cancer risk is increased with the amount of saturated animal fat in the diet (22, 23).

In a test carried out in the US, researchers investigated the cancer forming compounds (carcinogens) produced in cooking. All foods when heated to cooking temperatures produce these agents but some produce more than others. Researchers compared soya-based burgers, beef burgers and bacon, which were all cooked until well done. The beef burger produced 44 times more carcinogens than the soya burger and the bacon produced 346 times more (53).

The top 12 cancer fighting foods are:

Greens (eg beet, mustard, turnip, bok choi, broccoli, brussel sprouts, cabbage, chard, kale, watercress); Oats and other Wholegrains (eg wheat, rye, millet, quinoa); Berries (eg cranberries, blueberries, raspberries, blackberries); Garlic; Yams and Sweet Potatoes; Beans, Peas and Lentils of every kind; B12 fortified foods (see page 15); Flax seeds – ground up and oil; Miso and tofu and other soya products (not the highly refined ones such as mock meats).