If you’re following a high protein diet, you might want to put down your knife and fork. According to new findings an excessive protein intake linked to a higher risk of cancer death. What’s more, middle-aged people who eat plenty of animal protein-- including meat, milk and cheese -- are also more susceptible to early death in general.
After tracking 6,318 adults for nearly two decades, the researchers have found that eating a diet rich in animal proteins during middle age makes you four times more likely to die of cancer than someone with a low-protein diet -- a mortality risk factor comparable to smoking.
High-protein eaters were 74 percent more likely to die of any cause within the study period than their more low-protein counterparts. They were also several times more likely to die of diabetes.
But how much protein we should eat has long been a controversial topic – muddled by the popularity of protein-heavy diets such as Paleo and Atkins. Before this study, researchers had never shown a definitive correlation between high protein consumption and mortality risk.
The latest study considers how biology changes as we age, and how decisions in middle life may play out across the human lifespan. In other words, what's good for you at one age may be damaging at another.
Protein controls the growth hormone IGF-I, which helps our bodies grow but has been linked to cancer susceptibility. Levels of IGF-I drop off dramatically after age 65, leading to potential frailty and muscle loss. The study shows that while a high protein intake during middle age is harmful, it is protective for older adults: those over 65 who ate a moderate- or high-protein diet were less susceptible to disease.
Research shows that a low-protein diet in middle age is useful for preventing cancer and overall mortality, through a process that involves regulating IGF-I and possibly insulin levels. But the researchers from the University of Southern California 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 researchers found that plant-based proteins, such as those from beans, did not seem to have the same mortality effects as animal proteins. Rates of cancer and death also did not seem to be affected by controlling for carbohydrate or fat consumption, suggesting that animal protein is the main culprit.
These findings support recommendations from several leading health agencies to consume about 0.8 grams of protein per kilogram of body weight every day in middle age. For example, a 130-pound person should eat about 45-50 grams of protein a day, with preference for those derived from plants such as legumes, soy and nuts.
The researchers define a "high-protein" diet as deriving at least 20 percent of calories from protein, including both plant-based and animal-based protein. A "moderate" protein diet includes 10-19 percent of calories from protein, and a "low-protein" diet includes less than 10 percent protein.
Even moderate amounts of protein had detrimental effects during middle age, the researchers found. People who ate a moderate amount of protein were still three times more likely to die of cancer than those who ate a low-protein diet in middle age, the study shows. Overall, even the small change of decreasing protein intake from moderate levels to low levels reduced likelihood of early death by 21 percent.
For a smaller portion of the total participants (2,253 people), levels of the growth hormone IGF-I were recorded. The results show that for every 10 ng/ml increase in IGF-I, those on a high-protein diet were 9 percent more likely to die from cancer than those on a low-protein diet, in line with past research associating IGF-I levels to cancer risk.
The researchers also extended their findings about high-protein diets and mortality risk, looking at causality in mice and cellular models. In a study of tumor rates and progression among mice, the researchers show lower cancer incidence and 45 percent smaller average tumor size among mice on a low-protein diet than those on a high-protein diet by the end of the two-month experiment.
The researchers said, "Almost everyone is going to have a cancer cell or pre-cancer cell in them at some point. The question is: Does it progress? One of the major factors in determining if it does is protein intake."
Source: Cell Metabolism, March 4, 2014.
All research on this web site is the property of Leslie Beck Nutrition Consulting Inc. and is protected by copyright. Keep in mind that research on these matters continues daily and is subject to change. The information presented is not intended as a substitute for medical treatment. It is intended to provide ongoing support of your healthy lifestyle practices.