If you're a Women's Health reader, then we're guessing you would never even consider picking up a cigarette habit, given how awful smoking is for your health (right?!). But an alarming new study suggests that something plenty of health-conscious women are doing—eating animal-based proteins—may be almost as harmful.
For the study, which was published in the journal Cell Metabolism, researchers looked at data from the National Health and Examination Survey III (NHANES III), the only nationally representative dietary survey in the U.S. They divided participants into three categories: those who consumed no more than 10 percent of their daily calories from protein, those who consumed 10-20 percent of their daily calories from protein, and those who consumed more than 20 percent of their daily calories from protein. They then used the National Death Index to track participants' mortality over the 18 years following when data for NHANES III was collected.
Turns out, the people who consumed the highest level of protein and were 50-65 when NHANES III was conducted were 74 percent more likely to die for any reason during the 18-year span of the study—and they were more than four times more likely to die of cancer during that period than the other groups. This correlation held true even after researchers controlled for other factors such as socio-economic status, diseases, waist circumference, saturated fat intake, total fat intake, and carbohydrate intake. But when researchers controlled for participants' intake of animal-based protein, the correlation all but disappeared, suggesting that animal proteins may be responsible for a significant portion of these relationships. (When researchers controlled for plant-based protein intake, the correlation remained, suggesting they don't have the same effect.)
MORE: The Scary Side-Effect Associated with High-Protein Diets
Interestingly, the correlation between protein intake and mortality flip-flopped for participants over the age of 65: Higher protein intake was protective for overall mortality and cancer mortality in that age group.
While this study didn't look at why this relationship might exist, lead study author Morgan Levine Canon, a Ph.D. student in gerontology at the University of Southern California, says a growth hormone receptor called insulin-like growth factor 1 (IGF-1) may play a role: "For most people, at some point in their life, they will probably have a cancer cell or pre-cancer cell in their body," says Canon. "But what determines whether that cell progresses into a full-fledged cancer cell might be some of these growth hormones since cancer cells are very sensitive to growth hormones; that's what causes them to proliferate and grow out of control."
Meanwhile, animal studies suggest that low levels of IGF-1 have been associated with a longer life, possibly because they may allow cells to devote more energy to cell maintenance and repair (rather than growth), says Canon. (The effect may reverse later in life since IGF-1 levels naturally diminish with age and you need a certain amount to maintain healthy bodily functioning.)
So how does this translate into eating meat and dairy products being as bad for you as smoking? While this wasn't specifically discussed in the full text of the study, Valter Longo, director of the University of Southern California's Longevity Institute, told FoxNews.com, "Cancer mortality was higher for high-protein [eaters] compared to current smokers."
The stats do bear out—and these findings are pretty sobering—but it's important to keep in mind that there were some definite limitations to this study: For one thing, it's based on data compiled about one day's worth of eating for participants; although the survey respondents did answer questions about how typical these meals were for them, what they ate on that day can't possibly be a perfect reflection of how they ate over the next 18 years.
The survey also didn't distinguish between farm-raised meat consumption and factory-farmed meat consumption. "We know that there's a lot of hormones injected in animals, but unfortunately, the data we have doesn't provide information on that," says Canon. "I think down the road that's another study that people can look at in more detail."
There's another big factor worth considering here, too: This is one study saying that animal protein consumption may significantly increase your risk of cancer—and there's tons of research about how deadly smoking is. So while the results are certainly enough to make you think twice about how much chicken and yogurt you're consuming, that doesn't necessarily mean that eating these foods is just as bad as smoking. "The size of the effect we're finding was similar, however I think the association with smoking mortality is way more clear-cut," says Canon. "There's been a lot more research, and there's a lot less potential for confounding factors. For nutrition, it's really hard to unravel what someone's diet is and really quantify that—whereas it's quite easy to say, 'Do you smoke a pack of cigarettes a day?'"
Canon emphasizes that this definitely isn't a reason to continue (or start) smoking. If anything, she hopes it will encourage more people to cut back on their animal-based protein intake. "This is an association we're finding right now, and we recognize more work needs to be done with this," she says. "But there's a lot of evidence that probably eating plant-based is healthiest."
MORE: How to Become a Part-Time Vegan
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