High-Protein Diet Linked with Cancer, Early Death

Researchers at University of Southern California say that eating meat and cheese can increase cancer and early death risk and might be just as bad as smoking, especially for middle-aged people.

A diet high in animal protein- such as milk, cheese and meat- doesn't just increase cancer risk, but also early death risk in people less than 65 years of age, researchers found. In the study, meat-lovers were around 74 percent more likely to die early than people who stuck to a low-protein diet.

Nearly 6,318 adults over the age of 50 participated in the study. Average protein intake was 16 percent, two thirds of which came from animal protein.

Researchers found that people with moderate protein consumption had three times higher risk of dying due to cancer than people who ate a low-protein diet. It is a mortality risk factor comparable to smoking. Even a small decrease in total protein intake led to a 21 percent reduction in chances of early death.

"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 Valter Longo, from the USC Davis School of Gerontology, one of the study authors.

Recently, a related study showed that following a vegetarian diet protects the heart and helps increase longevity.

Protein is associated with regulation of growth hormone IGF-I. The hormone is known to increase cancer. However, by age 65, the body experiences a drop in IGF-I, which leads to poor muscle maintenance.

"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 Eileen Crimmins, 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."

Longo's previous research on Ecuadorian cohort showed that people with certain genetic mutation that lowers IGF-I had reduced risk of developing cancer or diabetes. The present study is an extension of that study.

Researchers found that beans did not increase cancer risk. They also controlled for carbohydrates and fats in the diet of the participants and found that none of these affected cancer risk, showing that animal protein was the reason for the health risks.

The study team also analyzed IGF-I levels in 2,253 randomly selected participants. Researchers found that for every 10 ng/ml increase in IGF-I, people on a high-protein diet had a 9 percent higher risk of death due to cancer, according to a news release.

Middle-aged people should limit their protein intake to 0.8 grams of protein per kilogram of body weight every day, according to Longo and team.

The study was funded by the National Institute of Aging of the National Institutes of Health and is published in the journal, Cell Metabolism.

Research has shown that it was meat and cooked food that helped humans evolve dramatically over a period of few million years. A related study found that humans might be hard-wired to eat protein.