Hard-core adherents of the faddish Paleo diet like to crow that eating like our über-great-ancestors is a way to beat the scourge of so-called modern diseases such as cancer. So what to make of a recent study published in the journal Cell Metabolism that found people who eat lots of protein in middle age are more likely to die of cancer than those who eat less? How much more likely? Four times. That puts the increased cancer risk on par with smoking.
True, there are a number of other things besides meat that you can eat if you go Paleo, such as fresh fruits and vegetables, nuts and seeds, and “healthful” oils such as olive oil and walnut oil (though how Paleolithic peoples were pressing their own oils does remain a mystery).
But when most people think Paleo, they think meat—and lots of it. Isn’t that the first thing that comes to mind, a honking drumstick à la Fred Flintstone? The average Paleo diet, according to a review in U.S. News & World Report, has about 38 percent of a day's calories coming from protein.
That’s far above the level researchers say is likely to cause increased cancer risk, at least for people between 50 and 65. The study, led by Valter Longo at the University of Southern California, defines a “high-protein” diet as deriving 20 percent or more of daily calories from protein. The study examined more than 6,000 participants ages 50 and older and followed them for 18 years.
“Popular diets in many cases have high proteins and low sugars. They may make you lose some weight, but that's not a good diet to increase life span,” Longo tells Scientific American. What's also likely to raise the ire of more Paleo fans is researchers’ assertion that people eschew animal-based proteins for plant-based ones like beans—a no-no for Paleos.
Working on the hunch that diet was tied to the increased cancer risk they observed in their human subjects, Longo and his team conducted a test that showed mice fed a high-protein diet had greater concentrations of a particular growth hormone in their blood that seemed to encourage tumor growth when they were injected with skin cancer cells.
"When you have a lot of protein, these growth factors go up, and we've shown that they help normal cells become cancer-like cells, and then they help the cells grow," Longo tells Scientific American.
Once you pass 65, however, the benefits of a low-protein diet (defined here as less than 10 percent of your daily calories) decline. In fact, people above retirement age seem to do best on a so-called “moderate” protein diet, meaning between 10 and 19 percent of daily calories are derived from protein. But the fact remains that Paleo diet levels of protein (or Atkins levels, for that matter) do not appear to correspond here with increased longevity—quite the opposite in fact.
Of course, evolutionary biologists such as Marlene Zuk, author of Paleofantasy, and other experts have long argued that the Paleo diet is more or less a mythical creation. While Paleolithic peoples clearly weren’t noshing on Twinkies and Doritos, there was likely widespread variety in what they ate, and there’s evidence, for example, that people were processing grain in some manner as far back as 30,000 years ago.
And it almost goes without saying that if you lived during the Paleolithic era, you would be exceptionally lucky to make it to 50 at all.