The biggest discrepancy is the level of salt and other preservatives: processed meats generally contain four times more sodium than red meats and 50 percent more preservatives, particularly chemical compounds known as nitrates and nitrites, which help to kill bacteria and give meat an appealing pink or red hue. Some processed meats also contain nitrosamines, which form nitrites when meat is cooked at high temperatures or exposed to the acidity of the human stomach. Salt has been linked to higher blood pressure in susceptible individuals. Nitrates harden arteries and trigger metabolic changes that mimic diabetes. And nitrosamines have been linked to cancer in rodents, monkeys and people. (Mozaffarian's study did not address cooking methods. Survey studies suggest that people who eat a lot of well-done, fried or barbecued meat are slightly more likely to develop colorectal or pancreatic cancer.)
Ultimately, evaluating someone's health based on meat consumption alone, while ignoring other dietary choices and personal habits, does not make sense. Although humans no longer depend on meat in the same way as our ancestors, red meat remains an important global source of protein, iron and vitamin B12. The best available evidence makes a convincing case against consuming too much processed red meat and overcooked meats but not necessarily against modest amounts of red meat. That is welcome news for those of us who enjoy the occasional steak—as well as for John Durant and his meat locker.
Editor's note: Originally, this article incorrectly stated that the large intestine grew over the course of human evolution; it was the small intestine. The text has been edited to amend this error.
SCIENTIFIC AMERICAN ONLINE
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This article was originally published with the title Meat of the Matter.