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5. Population nutrient intake goals for preventing diet-related chronic diseases: Previous page | 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27

The only dietary factors which have been shown to increase the risk for breast cancer are obesity and alcohol. Obesity increases breast cancer risk in postmenopausal women by around 50%, probably by increasing serum concentrations of free estradiol (43). Obesity does not increase risk among premenopausal women, but obesity in premenopausal women is likely to lead to obesity throughout life and therefore to an eventual increase in breast cancer risk. For alcohol, there is now a large body of data from well-designed studies which consistently shows a small increase in risk with increasing consumption, with about a 10% increase in risk for an average of one alcoholic drink every day (45) The mechanism for this association is not known, but may involve increases in estrogen levels (46).

The results of studies of other dietary factors including fat, meat, dairy products, fruits and vegetables, fibre and phyto-estrogens are inconclusive (9, 34, 47, 48).

Endometrial cancer. Endometrial cancer risk is about three-fold higher in obese women than in lean women (8, 49), probably because of the effects of obesity on hormone levels (50). Some case-control studies have suggested that diets high in fruits and vegetables may reduce risk and that diets high in saturated or total fat may increase risk, but the amount of available data is limited (9).

Prostate cancer. Prostate cancer incidence rates are strongly affected by diagnostic practices and therefore difficult to interpret, but mortality rates show that death from prostate cancer is about 10 times more common in North America and Europe than in Asia (11).

Little is known about the etiology of prostate cancer, although ecological studies suggest that it is positively associated with a “westernized” diet (19). The data from prospective studies have not established causal or protective associations for specific nutrients or dietary factors (9, 34). Diets high in red meat, dairy products and animal fat have frequently been implicated in the development of prostate cancer, although the data are not entirely consistent (9, 51-53). Randomized controlled trials have provided substantial, consistent evidence that supplements of b-carotene do not alter the risk for prostate cancer (40, 41, 54) but have suggested that vitamin E (54) and selenium (55) might have a protective effect. Lycopene, primarily from tomatoes, has been associated with a reduced risk in some observational studies, but the data are not consistent (56). Hormones control the growth of the prostate, and diet might influence prostate cancer risk by affecting hormone levels.

Kidney cancer. Overweight and obesity are established risk factors for cancer of the kidney, and may account for up to 30% of kidney cancers in both men and women (57).

Table 11 provides a summary of strength of evidence with regard to the role of various risk factors in the development of cancer.

Table 11. Summary of strength of evidence on lifestyle factors and the risk of developing cancer

Evidence

Decreased risk

Increased risk

Convincinga

Physical activity (colon)

Overweight and obesity (oesophagus, colorectum, breast in postmenopausal women, endometrium, kidney)
Alcohol (oral cavity, pharynx, larynx, oesophagus, liver, breast)
Aflatoxin (liver)
Chinese-style salted fish (nasopharynx)

Probablea

Fruits and vegetables (oral cavity, oesophagus, stomach, colorectumb)
Physical activity (breast)

Preserved meat (colorectum)
Salt-preserved foods and salt (stomach)
Very hot (thermally) drinks and food (oral cavity, pharynx, oesophagus)

Possible/insufficient

Fibre
Soya
Fish
n-3 Fatty acids
Carotenoids
Vitamins B2, B6, folate, B12, C, D, E
Calcium, zinc and selenium
Non-nutrient plant constituents (e.g. allium compounds, flavonoids, isoflavones, lignans)

Animal fats
Heterocyclic amines
Polycyclic aromatic hydrocarbons
Nitrosamines

a The "convincing" and "probable" categories in this report correspond to the "sufficient" category of the IARC report on weight control and physical activity (4) in terms of the public health and policy implications.
b For colorectal cancer, a protective effect of fruit and vegetable intake has been suggested by many case-control studies but this has not been supported by results of several large prospective studies, suggesting that if a benefit does exist it is likely to be modest.

The Consultation recognized the problems posed by the lack of data on diet and cancer from the developing world. There are very limited data from Africa, Asia and Latin America, yet these regions represent two-thirds or more of the world population. There is thus an urgent need for epidemiological research on diet and cancer in these regions. The need to evaluate the role of food processing methods, traditional and industrial, was also identified. Microbiological and chemical food contaminants may also contribute to carcinogenicity of diets.

The nutrition transition is accompanied by changes in prevalence of specific cancers. For some cancers, such as stomach cancer, this may be beneficial while for others, such as colorectal and breast cancers, the changes are adverse.

5.5.5 Disease-specific recommendations

The main recommendations for reducing the risk of developing cancer are as follows:

  • Maintain weight (among adults) such that BMI is in the range of 18.5-24.9 kg/m2 and avoid weight gain (>5 kg) during adult life (58).
  • Maintain regular physical activity. The primary goal should be to perform physical activity on most days of the week; 60 minutes per day of moderate-intensity activity, such as walking, may be needed to maintain healthy body weight in otherwise sedentary people. More vigorous activity, such as fast walking, may give some additional benefits for cancer prevention (4).
  • Consumption of alcoholic beverages is not recommended: if consumed, do not exceed two units1 per day.
  • Chinese-style fermented salted fish should only be consumed in moderation, especially during childhood. Overall consumption of salt-preserved foods and salt should be moderate.
  • Minimize exposure to aflatoxin in foods.
  • Have a diet which includes at least 400 g per day of total fruits and vegetables.
  • Those who are not vegetarian are advised to moderate consumption of preserved meat (e.g. sausages, salami, bacon, ham).2
  • Do not consume foods or drinks when they are at a very hot (scalding hot) temperature.

1 One unit is equivalent to approximately 10 g of alcohol and is provided by one glass of beer, wine or spirits.

2 Poultry and fish (except Chinese-style salted fish) have been studied and found not to be associated with increased risk for cancer.

5. Population nutrient intake goals for preventing diet-related chronic diseases: 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27 | Next page

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