Meat and cheese may be as bad as smoking.

• Position: Medicine & Health

That chicken wing you are eating could be as deadly as a cigarette. In a study that tracked a large sample of adults for nearly two decades, researchers have found that eating a diet rich in animal proteins during middle age makes a person four times more likely to die of cancer than someone with a low-protein diet--a mortality risk factor comparable to smoking.

"There's a misconception that, be cause we all eat, understanding nutrition is simple, but the question is not whether a certain diet allows you to do well for three days, but can it help you survive to be 100?" says Valter Longo, professor of biogerontology at the University of Southern California, Davis, and director of the USC Longevity Institute.

Not only is excessive protein consumption linked to a dramatic rise in cancer mortality, but middle-aged people who eat lots of proteins from animal sources--including meat, milk, and cheese--also are more susceptible to early death in general. Protein lovers are 74% more likely to die of any cause than their more low-protein counterparts. They also are several times more likely to die of diabetes.

How much protein one should eat long has been a controversial topic--muddled by the popularity of protein-heavy diets such as Paleo and Atkins. Before this study, researchers never had shown a definitive correlation between high-protein consumption and mortality risk.

Rather than look at adulthood as one monolithic phase of life, as other research has done, this study considers how biology changes as we age...