Tuesday, March 1, 2011
Meat and Cancer: The Carnivore's Conundrum
A review published last week by the British Nutrition Foundation (and funded by the UK meat industry) found no evidence that eating moderate amounts of lean red meat has negative health effects. "Hurrah - eating red meat is good for you!" Britain's Daily Mail cheered.
At the other end of the spectrum, the British Vegan and Vegetarian Foundation issued a press release saying that women wishing to lower their risk of breast cancer "should reduce the amount of meat they eat and cut down - or even cut out - dairy produce."
The World Cancer Research Fund on its blog responded by pointing out that this recommendation was based on research that had not actually investigated the link between animal foods and breast cancer. "This press release is likely to hinder, rather than help, people's ability to make informed choices," it concluded.
In-between these poles, the British government said in its Iron & Health Report that while red meat is a valuable source of iron, eating too much could lead to cancer and heart disease. It recommended that people consuming more than 90g (3.2 oz) per day of red and processed meat should reduce intakes to 70g (2.5 oz) per day or less. (This is equivalent to two standard beef burgers; one lamb chop; two slices of roast lamb, beef or pork; or three slices of ham.)
This tallies with the WCRF's recommendation that adults should eat no more than 500g (1.1 lb; cooked weight) red meat per week, though the cancer research and education charity makes a clear distinction between "red" and "processed" meat, advising people to avoid the latter wherever possible.
Where does this leave the confused carnivore? Should we avoid red meat and only eat poultry and fish? Should we stop eating meat altogether? Or is there a safe way of enjoying red meat?
I asked Denis Corpet, Professor of Food Hygiene and Human Nutrition at the University of Toulouse, for his views on the matter. Professor Corpet heads the "Prevention and Promotion of Carcinogenesis by Foods" research team at the ToxAlim center of France's public agriculture research agency INRA.
CMW: What is the colon-cancer risk of eating red and processed meat?
DC: Meat is not carcinogenic, but people eating lots of meat develop cancer more often than those who eat it less. In Europe, twenty percent of people eat more than 80g beef per day, and they are more likely to develop colon cancer than those eating meat rarely. The risk increase is modest, between +20% and +30%. The same risk is observed in people eating more than 50g deli (cured meat) per day.
From an individual perspective, this is not a huge increase. It means that one person out of 20 will get colorectal cancer, and in big meat eaters this value becomes 1.2 person out of 20. But from a public health perspective, each day one hundred people in France are told they have colorectal cancer. The excess risk associated with a daily steak, +25%, now translates to an extra 25 people each day with cancer!
CMW : Is red meat implicated in any other cancers?
DC: The link between meat and cancer was discovered with stomach and colorectal cancer. The link seems much weaker with breast and prostate cancers, and did not show up even in the very large European EPIC study of half a million persons. In an American study of similar size, elevated risks (from 20% to 60%) were evident for esophageal, colorectal, liver, and lung cancer, but not breast or prostate.
CMW: What are the cancer risks inherent in red meat?
DC: Nobody knows exactly why red meat is (slightly) toxic, but we have "hypotheses," that is, various paths to track down the villain. A tasty BBQ steak could be bad for you because it's fatty, grilled, or "red."
Yes, too much fat increases our risk of obesity, which is a cause of cancer. But dietary fat in itself is not carcinogenic.
Yes, the black-brown part of a grilled steak contains potent carcinogens (named, for instance, PhIP, MeIQx, BaP), but the doses are very low and it is hard to believe they could give us cancer.
Yes, beef is red because it contains heminic iron, which our body needs to make our own red blood and red muscles. In my laboratory we found that that rats given heminic iron (or beef meat) after being injected with carcinogens had more tumors than controls given the shot but not the iron-rich diet. Thus "the red" in red meat clearly promotes cancer.
CMW : What are the cancer risks inherent in processed meat?
DC: Most processed meats are made from red meat (pork is red, even if it has less iron than beef), and ham and sausages are often fatty and grilled; thus the same risks are present in beef and in cured meat.
In addition, cured meat is made by adding salt (no effect on the colon, but bad for the stomach) and nitrites. Nitrites provide four benefits: fewer bacteria (particularly the killer botulism), less oxidation (no rancidity), better color (red instead of brown, pink instead of grey when cooked) and better flavor (the "deli" taste). But nitrites may form carcinogenic substances called nitrosamines, or related toxic compounds we call NOCs, and my lab has shown that these promote tumors in rats.
CMW : Are there risks in not eating red or processed meat?
DC: Meat is good for you. We need protein, and meat provides excellent proteins, though we can also get protein from other foods. We need iron, zinc and vitamin B12, and it is very hard to find those elsewhere than in meat. This is why I would not advise people to give up red meat, but to eat at least one steak a week. Many young women dislike red meat and become anemic: as the iron stores in their bodies decline they cannot make enough red blood cells and this can lead to constant tiredness and a pale complexion.
In contrast we do not NEED to eat cured meat. Its benefits are the same as those of red meat, but because it seems twice as toxic, it's better to eat fresh than processed meat.
CMW: Observational studies show that red meat consumption is associated with a higher risk of cancer; are these studies reliable? What experimental evidence is there for the meat/cancer link?
DC: Epidemiological observations do not "prove" the cause and effect link. This is why I chose to work experimentally on this question about ten years ago. The problem is that this type of research cannot be done on humans. We thus provide strong evidence that red meat, cured meat, and heminic iron, promote tumors in rats and mice. This does not translate directly to humans, but bringing together observations in people and experiments in rodents seems to provide a compelling picture.
CMW: How can people who eat red meat regularly cut their cancer risk?
DC: It is wise not to eat red meat too often, and to have small portions in line with the WCRF's guidelines. In addition, people who are afraid of fat should choose lean meat. And people who worry about carcinogens should not fry, grill or barbeque their steak, but eat slowly cooked red meat instead.
For those who think, as I do, that heminic iron could be the villain, a good way to reduce their risk is by consuming calcium with an iron-rich meal (calcium lowers the absorption of iron from food); for instance, by eating a yogurt or a piece of cheese after a steak.
CMW : Is there a way of lowering the risks from processed meat?
DC: In my laboratory we are testing specific substances that could be added during the curing process to "protect" meat so it does not promote tumors in rats. We already have shown, but not yet published, that added calcium and vitamin E can block the toxic process. We are now investigating the possible protective effects of natural polyphenols, like those that lend red wine and green tea their color and flavor.
I would advise against eating processed meat without nitrites (preservatives) because the deadly botulism bacterium remains a risk. Overall, it's enough to eat cured meat rarely: For instance I never buy ham or sausage, nor do I chose it at the cafeteria. But when I am invited to dinner at a friend's house, I eat whatever they serve me, most often with delectation (I just love the French "saucisson").
Professor Corpet's personal website provides articles he has published about his work (http://fcorpet.free.fr/Denis/Science.html), lecture notes and some of his favourite healthy recipes (http://fcorpet.free.fr/SalmonRecipe.html).