A diet rich in meat, eggs, milk and cheese could be as harmful to health as smoking, according to a controversial study into the impact of protein consumption on longevity.
Research which tracked thousands of adults for nearly 20 years found that people who eat a diet rich in animal protein are four times more likely to die of cancer than someone with a low protein diet. The risk is nearly as high as the danger of developing cancer by smoking 20 cigarettes each day. Previous studies have shown a link between cancer and red meat, but it is the first time research has measured the risk of death caused by regularly eating too much protein.
The US study -recently published in Journal Cell Metabolism- found that people with a high protein diet were 74% more likely to die of any cause within the study period than their low-protein counterparts. They were also several times more likely to die of diabetes. But this trend appeared to reverse for those aged over 65, researchers found.
High-protein food plans, such as the Atkins Diet, have become popular in recent years because of their dramatic weight-loss results. The new research from the University of Southern California suggests that such dieters may harm themselves in the long run.
“We provide convincing evidence that a high-protein diet – particularly if the proteins are derived from animals – is nearly as bad as smoking for your health,” said Dr Valter Longo, of the University.
The researchers define a “high-protein” diet as deriving at least 20% of daily calories from protein. They recommend consuming about 0.8g (0.03oz) of protein per kilogram of body weight every day in middle age. It means a person weighing nine stone should eat about 45-50g (1.6-1.7oz) of protein a day. A 300g (10.5oz) steak contains 77g (2.7oz) of protein.
As well as red meat, dairy products high in protein are also dangerous, the researchers said. A 200ml (7fl oz) glass of milk represents 12% of the recommended daily allowance, while a 40g (1.4oz) slice of cheese contains 20%. Chicken, fish, pulses, vegetables, nuts and grain are healthier sources of protein. However, a chicken breast or salmon fillet still accounts for about 40 per cent of recommended daily protein intake.
“The research shows that a low-protein diet in middle age is useful for preventing cancer and overall mortality,” said Dr Eileen Crimmins, a co-author of the study.
“However, we also propose that at older ages, it may be important to avoid a low-protein diet to allow the maintenance of healthy weight and protection from frailty.”
The backlashSo 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 the press “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.
- Furthermore, there was also no distinction between animal proteins — some people could have been eating skinless white chicken breast or steamed fish instead of bacon and sausages.
- 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 Morgan Levine Canon, a Ph.D. student in gerontology at the University of Southern California. “I think down the road that's another study that people can look at in more detail.”
Bottom line
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.”
