Vegetarianism and cancer
Respected epidemiologists Doll and Peto estimated that 35% of cancer mortality in the USA is related to diet (1). This relationship is particularly evident for cancers of the digestive and reproductive systems.
Breast cancer
Several studies have correlated the per capita consumption of various foods in up to 41 countries with cancer mortality in those countries. In each study, the rate of breast cancer was highly correlated with total fat consumption, especially animal fat (2-5). This relationship existed even when average height, weight, and age at first menstruation were taken into account (5).
Other studies have compared different ethnic groups in one region, such as Hawaii, or compared different groups undergoing social change, as in Japan and Singapore.
The diets of over 4600 adults from the 5 main ethnic groups in Hawaii were recorded and related to the incidence of breast cancer in those groups. Cancer rate was related to total fat intake, as well as animal, saturated, and unsaturated fat intake (6).
When Japanese and Caucasian women in Hawaii with breast cancer were matched to women without breast cancer, those with cancer were found to consume more total fat, saturated fat and animal protein, except in the younger group of Caucasians (7).
Among Japanese in Hawaii, breast cancer was associated with change to an American diet. Dietary information was available for men, and it was assumed that their wives would eat a similar style of diet. Men whose wives had breast cancer ate more meat and fatty foods such as butter and cheese, whereas those whose wives didn't have cancer ate more traditional Japanese foods, including green tea and seaweeds (8).
Western influence has become stronger in Japan since World War II; some Japanese have adopted more western customs, including diet, whereas others have not. Traditionally the Japanese had a low rate of breast cancer, although the number of deaths due to this disease doubled in the period 1955-1975. In a study of over 142,000 women over a 10-year period, women who ate meat daily were much more likely to develop breast cancer than women who never or only occasionally ate meat. Across 12 districts of Japan, the incidence of breast cancer was correlated with per capita consumption of animal fat, in particular intake of pork (9).
Some Chinese in Singapore have also westernised their diets. Women with breast cancer had a higher intake of red meat than a matched control group without cancer, while the control group had a higher intake of soy protein and soy products (10).
In all these studies there was a wide variation in diet between countries, between ethnic groups in the same country, or between more and less traditional groups of the same ethnic background. In all cases, breast cancer was associated with a higher intake of animal fat, especially from meat. However, this relationship is not always found when the groups being compared are more similar, and both are eating a relatively high fat western diet.
Case control studies involve comparing women who have breast cancer with otherwise similar, healthy women. One such study in Canada found that breast cancer was associated with the frequency of eating beef and pork (11), while another in Israel found that breast cancer was associated with high fat and animal protein intake, and low fibre intake (12).
In another case control study in Canada, breast cancer was associated with total fat intake, rather than fat from a particular source (13). Among women with breast cancer in the USA, those in the top two-thirds of total fat intake were twice as likely to die of their disease as women in the bottom third (14).
Two case control studies in Italy found that breast cancer was associated with intake of dairy products (15-16). Italy has a wide variation in diet, and fat intake among the women studied ranged from 26%-46% of total calories (16). The researchers commented: "... a diet rich in saturated fat or animal proteins may be associated with a twofold to threefold increase in a woman's risk of breast cancer " (16). Another case control study in France found that higher risk of breast cancer was associated with increasing consumption of cheese and milk, but not yoghurt (17).
In the USA, per capita consumption of milk products was associated with deaths due to breast cancer across 48 states (18). Milk products could have an effect, not only through the fat they contain, but also through Insulin-like Growth Factor (IGF) in the milk. IGF-1 causes breast cancer cells to proliferate in laboratory studies, and highly malignant breast cancers are known to produce IGF-1 (19).
Some case control studies in the USA (20-21), Australia (22) and Greece (23) have not found any association between breast cancer and fat intake. Californian Seventh-Day Adventists have 79% the risk of developing breast cancer compared to the general population, but within the SDA group, the risk of cancer was not associated with any particular group of animal products (24). However, vegans did have a lower risk of dying of breast cancer.
Other studies did not find a lower death rate due to breast cancer among vegetarian nuns in a strict religious order and the general population (25), or members of the UK Vegetarian Society and the general population (26).
Two prospective studies in the USA did not find any association between dietary fat intake and breast cancer. In one, over 5400 women were followed for 10 years (27), while in the other over 89,000 nurses were followed for 4 years (28). Those who developed breast cancer during the study did not consume more fat than women who remained healthy. However, in both cases the women at a relatively high fat diet. For example, the nurses ate 32-44% of total calories as fat. It is likely that fat intake has to be much lower than this to have a protective effect.
High levels of oestrogens in the blood are thought to be a risk factor for breast cancer. Recent Asian immigrants to America had 32% lower levels of such oestrogens than Caucasians. The former ate about 20% of calories as fat, compared to around 40% among the latter (29). Vegetarians have lower levels of oestrogens in the blood than meat eaters (30), and vegans consuming a 22% fat diet have lower levels than vegetarians (31). When meat eaters change to a low fat diet (20-25% fat), their levels of oestrogens decline (32).
Apart from the negative effect of animal fat in particular, plants may actually have a positive effect through the oestrogens they contain. These weak phyto-oestrogens bind to receptors in the body, but without the damaging effects of the body's own hormones. The phyto-oestrogens come in the form of lignans, found in grains, nuts, seeds and legumes, and isoflavones, found in tropical legumes such as soy beans (33).
The isoflavones in soy products are particularly powerful, and some researchers have speculated that soy protein could be as effective as the drug Tamoxifen in reducing oestrogens and breast cancer (33). Evidence from Singapore suggests that soy products have a protective effect against breast cancer (10).
While the research on breast cancer is not unequivocal, there is enough evidence to suggest that a low fat vegan diet, preferably containing soy products, is the best way to reduce the risk of this disease. Regular exercise also has a positive effect, whereas alcohol may have a negative effect.
Other reproductive cancers
Cancers of the ovary, uterus and prostate also seem to be diet-related. In the case of ovarian cancer, a comparison across 30 countries showed that cancer death were associated with higher per capita consumption of total fat, in particular animal fat. Deaths were also related to meat and milk consumption, while higher intake of vegetables and grains had a protective effect (2).
Californian Seventh-Day Adventists had a lower risk of ovarian cancer than the general population (RR=0.61). Within the SDA group, cancer deaths were strongly associated with intake of eggs and fried foods, less so with meat (34).
A case control study in Canada found that ovarian cancer was associated with saturated fat intake, particularly egg consumption. Vegetables again had a protective effect (35). Another case control study in Shanghai similarly found that cancer of the ovary was associated with animal fat consumption, with a tendency for vegetables to be protective (36). A study of 16,000 people in Norway showed that women who drank 2 or more glasses of milk a day had a substantially higher risk of ovarian cancer than women who drank less (37).
In a case control study in China, women in the highest quarter for both animal fat and animal protein intake were 4.3 times more likely to have cancer of the uterus than women in the lowest quarter. Intake of meat, eggs and fresh fish were all associated with cancer (38). That a western diet high in animal products is implicated is also suggested by the fact that Chinese women in California have a 5 times higher rate of cancer of the uterus than women in Shanghai (38).
In a comparison across 29 countries, the death rates from prostate cancer were related to per capita fat intake, but only animal and not plant fat. There was a strong correlation with milk consumption, and a weaker one with meat consumption. Intake of grains had a protective effect (2).
Among Californian SDAs, the risk of prostate cancer was only slightly reduced compared to the general population (RR=0.93). The small size of this difference is not surprising in light of the fact that milk consumption was the factor most strongly associated with prostate cancer, and SDAs tend to consume a lot of dairy products. Meat (including poultry), cheese and eggs, considered separately, were less strongly associated, but men who had a high intake of each of these 4 animal products were 3.6 times more likely to die of prostate cancer than men whose intake of each of the 4 animal products was low (39).
Among over 51,000 professional men in the USA, those who had advanced prostate cancer consumed more animal fat, especially from meat, butter and bacon than men who remained cancer free (40). In over 4600 men from 5 ethnic groups in Hawaii, prostate cancer was associated with intake of animal fat and saturated fat (6). A case control study in Hawaii showed the same relationship in men aged 70 or more (7).
In a case control study in the USA, risk of prostate cancer was associated with total fat, animal fat, and meat and fish consumption (41). Two further case control studies linked prostate cancer to intake of dairy products. In a US study, men who drank 3 or more glasses of whole milk per day had a 2.5 times higher risk of prostate cancer than those who never drank milk (42). In an Italian study, men who ate dairy products more frequently had a 2.5 times higher risk of prostate cancer than men who ate them less frequently. Men with prostate cancer also tended to eat more meat (43).
As in the case of breast cancer, there is enough evidence to suggest that a vegan diet containing no animal fat and high in grains and vegetables is the best way to reduce the risk of cancers of the ovary, uterus and prostate.
Go to Vegetarianism and colon cancer .
I would like to see References for this document on Vegetarianism and Cancer.
Back to first page of Vegetarian Health
Go to Vegetarianism and Heart Disease
Go to Vegetarian Nutrition
Go to Vegetarian Questions and Answers
Go to Meat Eating and the Environment
Go to Quotes from Famous Vegetarians
Go to Vegetarian Recipes
http://www.animalliberation.org.au/vegocanc.html - Fri Jun 12 20:29:18 1998