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See Inside Scientific American Volume 307, Issue 6

Meat of the Matter: Are Our Modern Methods of Preserving and Cooking Meat Healthy?

Why steaks could be in but hot dogs are still out

Regularly eating meat and cooked foods changed our anatomy. Our teeth became smaller and less pointy, our colons shrank and our small intestines grew, all of which improved our ability to chew and digest soft, cooked foods.* Calorie-dense meats likely enabled the tripling of our brain size as well. These and other adaptations helped our ancestors survive in a time very different from our own. The pertinent questions for today are whether the diets of our evolutionary past have any bearing on our current situation and how our modern approaches to preparing and consuming meat change our health.

Reservations about Preservation

In trying to answer these questions, it is important to note right away that nutrition research is notoriously difficult to conduct. After all, scientists cannot ethically force some people to dine exclusively on red meat while others munch on lettuce to demonstrate the long-term health effects once and for all. But researchers have done the next best thing: surveying large groups of people about their diets.

Two studies from different teams of Harvard researchers exemplify the growing recognition that not all types of meat are equally unhealthy. This past spring Frank Hu and his colleagues concluded that eating red meat was indeed linked to a greater risk of cardiovascular disease, cancer and death from any cause. Specifically, each additional daily serving of unprocessed red meat (a serving is about the size of a deck of cards) increased the chances that someone would die by 13 percent; processed meat bumped up the death risk to 20 percent. These risks were calculated over a 22-year period for men and 28 years for women.

Translating those numbers into everyday terms requires some sophisticated math. Statistician David Spiegelhalter of the University of Cambridge used Hu's results to calculate that an adult who eats an extra serving of red meat each day would lose one year of life expectancy. Consider what that means for a healthy 40-year-old male, who can be expected to live another 36.2 years, according to FindtheData.org's analysis of the relevant Social Security data. Instead of making it just past his 76th birthday, he instead lives to 75.2 years. Nothing to shrug off—but certainly not the most deadly habit. Men and women who smoke, for example, lose an average of 13.2 and 14.5 years of life, respectively according to the Centers for Disease Control and Prevention.

Hu's study was not without limitations. It relied on self-reported surveys, which can skew the results in several ways. Equally problematic, it turns out that the participants who ate the most red meat were also more likely to smoke, drink alcohol in excess and exercise less often, making meat consumption seem unhealthier than it may truly be.

An alternative to Hu's conclusions emerged from another team at Harvard, led by Mozaffarian, who compiled and reviewed the results of 20 studies on eating meat. These 20 studies included data from more than 1.2 million people, whereas Hu's study looked at data from just over 120,000. The meta-analysis found no greater risk of death or disease tied to red meat in general; instead it singled out the dangers of processed red meat, such as bacon, salami and hot dogs. Mozaffarian and his colleagues associated each daily 50-gram serving of processed red meat with a 42 percent higher risk of heart disease and a 19 percent higher risk of diabetes.

As in Hu's study, people who eat a lot of hot dogs and cold cuts might be less healthy overall. But such strong associations from a large review are nonetheless intriguing. Why would processed red meat be so much worse than unprocessed red meat? Both have fairly similar levels of saturated and unsaturated fats. In every 50-gram serving, however, processed meats contain more calories and less cholesterol, protein and iron than red meat.

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