Foods from animal sources
Animal foods is a term used to describe all foods of animal origin. These foods may be derived from the animal flesh itself (for example, meat, fish and poultry) or foods that are produced by animals (for example, eggs, as well as dairy products such as milk and products made from milk including cheese, butter, ghee and yoghurt)
Animal foods are generally a good source of protein, but the fat content varies according to the specific species from which they are derived. Dairy products are a good source of calcium. Consumption of foods such as red meat and fish generally increases with economic development, whereas consumption of dairy products is variable, particularly in Asia where many populations are lactose intolerant.
Animal foods such as meat and fish may be processed before consumption by smoking, curing, salting or by adding preservatives. Meat and fish are also often cooked using very high temperatures during frying, grilling (broiling) or barbecuing (charbroiling). These methods of processing and preparation may affect the chemical composition as well as the nutritional value of animal foods.
OUR MAJOR FINDINGS ON CANCER AND ANIMAL FOODS
There is strong evidence that consuming:
For people who eat meat, eat no more than moderate amounts of red meat, such as beef, pork and lamb, and eat little, if any, processed meat
– This is the opinion of the Expert Panel and forms the basis of our Recommendation on red and processed meat
For red meat, processed meat and Cantonese-style salted fish the evidence shows that, in general, the more people consume, the higher the risk of some cancers. In contrast, the evidence shows that, in general, the more dairy products people consume, the lower the risk of colorectal cancer.
Cancer Prevention Recommendation
A global recommendation about consumption of Cantonese-style salted fish has not been made as this type of fish is consumed only in specific parts of the world. Nevertheless, the Panel advises that Cantonese-style salted fish should not be consumed.
The Panel did not base a recommendation on the strong evidence that the consumption of dairy products decreases the risk of colorectal cancer as there is some other evidence that is suggestive of an increased risk of prostate cancer, although that evidence fell below the general threshold required for making a recommendation. For more information on when the evidence is divergent between cancer sites, download the chapter of the Third Expert Report on Recommendations.
This section covers the primary hypotheses and is not based on a systematic or exhaustive search of the literature.
Red meat and cancer
Cooking meats at high temperatures, prolonged exposure to heat and cooking by various types of grilling results in the formation of heterocyclic amines and polycyclic aromatic hydrocarbons both of which have been linked to colorectal cancer development in experimental studies.
In addition, haem iron, which is present at high levels in red meat, has been shown to promote colorectal tumorigenesis by stimulating the endogenous formation of carcinogenic N-nitroso compound.
Polycyclic aromatic hydrocarbons, which are formed when organic substances like meat are burnt incompletely, may also have carcinogenic potential. Grilling (broiling) and barbecuing (charbroiling) meat, fish, or other foods with intense heat over a direct flame results in fat dropping on the hot fire, causing flames; these flames contain polycyclic aromatic hydrocarbons that stick to the surface of food.
Processed meat and cancer
Overall it is likely that a combination of mechanisms contribute to higher risk of colorectal cancer among people consuming high quantities of processed meat. Similar to red meat, processed meat is rich in fat, protein and haem iron which can promote tumorigenesis through the mechanisms described above.
Processed meats are often cooked at high temperatures which can lead to increased exposure to heterocyclic amines and polycyclic aromatic hydrocarbons.
Processed meat is invariably higher in fat content than red meat which may promote carcinogenesis through synthesis of secondary bile acids; however, human data supporting this hypothesis are weak.
Processed meat is also a source of exogenously derived N-nitroso compounds, which may have carcinogenic potential.
Dairy and cancer
Observed inverse associations between intake of dairy products and colorectal cancer development have been largely attributed to their high calcium content. In addition to calcium, lactic acid-producing bacteria may also protect against colorectal cancer,
while the casein and lactose in milk may increase calcium bioavailability. Other nutrients or bioactive constituents in dairy products, such as lactoferrin, vitamin D (from fortified dairy products) or the short-chain fatty acid butyrate may also impart some protective functions against colorectal cancer, but these require much better elucidation.
The CUP Panel concluded that the evidence was generally consistent for dairy products, milk, cheese and dietary calcium, and showed a decreased risk of colorectal cancer with higher consumption.
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