Washington, United States (ISJ): The chicken wing you are eating could be as deadly as a cigarette. A new study by researchers at the University of South California claims, the mortality risk factor of eating animal protein-rich diet during middle age is four times more ? comparable to smoking - than someone with a low-protein diet.
"There's a misconception that because 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?" said the lead author of the research, Valter Longo of the University of South California
Excessive protein consumption is linked to a dramatic rise in cancer mortality. Middle-aged people who eat lots of proteins from animal sources ? including meat, milk and cheese ? are more susceptible to early death in general, revealed the study published in Cell Metabolism. They are also more vulnerable to die of diabetes, claims the study.
This is the first time, research has shown a definitive correlation between high-protein consumption and mortality risk. The latest study also considers how biology changes as we age and how decisions in middle life may play out across the human life span, explains a news release by the University.
Protein controls the growth hormone IGF-I (insulin-type growth factor 1), which helps our bodies grow but has been linked to cancer susceptibility. Levels of IGF-I drop off dramatically after the age of 65, leading to potential frailty and muscle loss. The study shows that while high-protein intake during middle age is very harmful, it is protective for older adults: those over 65 who ate a moderate- or high-protein diet were less susceptible to disease.
"The 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," said co-author of the study Eileen Crimmins, also at the University of South California. "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."
Alternatively, the researchers found 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 carbohydrate or fat consumption, suggesting that animal protein is the main culprit.
Longo's 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 58-60 kgs person should eat about 45 to 50 grams of protein a day, preferably plant protein, Longo explained.
Even moderate amounts of protein had detrimental effects during middle age, the researchers found. Across all 6,318 adults over the age of 50 in the study, average protein intake was about 16 percent of total daily calories with about two-thirds from animal protein. The study sample was representative across ethnicity, education and health backgrounds.
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 showed. Overall, even the small change of decreasing protein intake from moderate levels to low levels reduced likelihood of early death by 21 percent.
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 showed 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.
"Almost everyone is going to have a cancer cell or pre-cancer cell in them at some point. The question is: Does it progress?" Longo said. "Turns out one of the major factors in determining if it does is protein intake."