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Cancer is now a major cause of mortality. This is largely due to the fact that people tend to live longer, with fewer people dying from other causes such as infectious diseases. In 2000, over 6 million people died from cancer, and there were an estimated 10 million new cases. Between 2000 and 2020, the total number of cases of cancer is predicted to increase by 73% in the developing world and by 29% in the developed world, largely as a result of an increase in the number of old people.
Cancer is caused by a variety of identified and unidentified factors. The most important proven cause of cancer is tobacco smoking. Other important factors include diet, alcohol consumption, physical activity, infectious diseases, hormonal factors and exposure to radiation. The incidence of lung, colon and rectum, breast, and prostrate cancer tends to be higher in developed countries, whereas the incidence of stomach cancer is higher in less developed countries.
This text is a summary of: WHO/FAO
Diet, Nutrition and the prevention of chronic diseases
Section 5.5.1 Background – 5.5.2 Trend
The likelihood of developing cancer may increase or decrease depending on what people eat how often they exercise. Dietary factors are estimated to account for approximately 30% of cancers in industrialized countries, making diet second only to tobacco as a theoretically preventable cause of cancer.
Research to date has uncovered few definite relationships between specific dietary factors and cancer risk.
Factors for which there is evidence of an increased risk include:
Overall, about 20-33% of cancers affecting the breasts, colon, uterus lining, kidney and oesophagus are attributable to unhealthy body weight and lack of physical activity.
Studies have investigated the specific role of diet in the development of major cancers
Lung cancer is the most common cancer in the world and over 80% of cases in developed countries are caused by tobacco smoking. The possible preventive effect of fruit and vegetables consumption against lung cancer remains controversial.
Risk factors in developing oral cavity, pharynx and oesophagus cancers seem to vary between countries. In developed countries, alcohol and tobacco alone cause up to 75% of these cancers. In developing countries, 60% of these cancers are attributed to a diet low in fruits, vegetables and animal products. Throughout the world, consuming extremely hot (thermally) drinks and food increases the risk of these cancers.
The risk of developing cancer of the uterus lining is greater in women who are obese, probably because of changes in hormone levels. Some studies suggest that a diet high in fruits and vegetables and low in fat might reduce the risk in developing endometrial cancer.
Overweight and obesity may cause up to 30% of kidney cancer cases.
Changes in diet and nutrition may play an important role in the increasing frequency of specific cancers. However, though Africa, Asia and Latin America represent two thirds or more of the world population, data on diet and cancer from these regions is lacking and more research is needed. Traditional and industrial food processing methods as well as microbiological and chemical food contaminants are factors that may contribute to the carcinogenicity of diets.
Table 11: Summary of strength of evidence
on lifestyle factors and the risk of developing cancer
This text is a summary of: WHO/FAO
Diet, Nutrition and the prevention of chronic diseases
Section 5.5.3 Diet, physical activity and cancer – 5.5.4 Strength of evidence
Although stomach cancer was once the most common cancer in the world, the number of deaths from this type of cancer have been decreasing over the past 20 years in all developed countries. Dietary factors are thought to play an important role and substantial evidence suggests that a high intake of salty, preserved foods can increase the risk of stomach cancer, whilst a diet rich in fruits and vegetables may reduce the risk. A bacterial infection of the stomach (helicobacter pylori) is known to contribute to an increased risk.
Liver cancer occurs much more frequently in developing regions such as sub-Saharan Africa and Southeast Asia. In these regions liver cancer is closely linked to certain infections (hepatitis B or hepatitis C) and to eating foods that have been contaminated by a toxic substance produced by certain molds (aflatoxin). In North America and Europe, excessive alcohol consumption is the main dietary risk factor for liver cancer.
This text is a summary of: WHO/FAO
Diet, Nutrition and the prevention of chronic diseases
Section 5.5.4 Strength of evidence
Colorectal cancers occur ten times more frequently in developed countries than in developing countries. This difference might largely be explained by international variations in diet. Aspects linked with the Western diet, such as a high intake of fat and preserved meat or overweight, seem to increase the risk of colorectal cancer. A high intake of dietary fibre, folate, calcium, and fruits and vegetables might decrease the risk of colorectal cancer. In addition, increased physical activity has been consistently associated with a reduced rate of colon cancer.
Cancer of the pancreas is more common in developed countries than in developing countries. Overweight might increase the risk of developing pancreatic cancer. Moreover, the risk might increase with a high intake of meat, and decrease with a high intake of vegetables.
Breast cancer is the second most common cancer in the world and the most common among women. It occurs much more frequently in developed countries than in less developed countries. This may reflect differences in risk factors linked to reproduction, such as age at the onset of menstruation, age of giving birth, number of children, and breastfeeding. Differences in dietary habits and physical activity may also contribute. Although obesity affects women of all ages, it only increases the risk of developing breast cancer in postmenopausal women. Many studies have shown a small increase in risk of breast cancer as alcohol consumption increases.
Mortality rates from prostate cancer are ten times higher in North America and Europe than in Asia, though figures are difficult to compare between countries because of different diagnostic practices. It is not yet clear if and how diet may influence the development of prostate cancer.
This text is a summary of: WHO/FAO
Diet, Nutrition and the prevention of chronic diseases
Section 5.5.4 Strength of evidence
The main diet and exercise-related recommendations for reducing the risk of cancers are as follows:
This text is a summary of: WHO/FAO
Diet, Nutrition and the prevention of chronic diseases
Section 5.5.5 Disease-specific recommendations
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