By Ian Lewis
Middle-aged people who eat a lot of animal protein may be increasing their risk of dying from cancer by as much as those who smoke a packet of cigarettes every day, a new study suggests.
The findings cast further doubt on the long-term benefits of following high protein eating regimes such as the Atkins or Paleo diets.
Researchers studying a group of more than 6,300 50 to 65-year-olds found that for those with high levels of animal protein in their diet the chances of dying from cancer was four times higher than among those with a low protein diet.
This a risk equivalent to that associated with smoking 20 cigarettes a day.
Red meat, milk and cheese most dangerous
And the team at the University of Southern California in the US found that a high protein diet was linked to 74% higher risk of early death from any cause, compared to people with low protein intakes.
The study defined a high protein diet as one which saw people getting at least a fifth of their daily calories from protein.
It found that animal-based proteins like red meat, milk and cheese are the most dangerous but found no evidence to suggest that fish protein had a negative effect on health.
And it recommends that middle-aged people should be eating around 0.8g of protein per kilo of bodyweight a day.
'Some proteins better than others'
The study's author, Dr Valter Longo said: "High levels of protein can be can be as bad for you as smoking.
"People should understand the distinction and be able to make the decision about what they eat.
"Some proteins are better for you than others, for example plant-based proteins like beans. Vegans seem to do better in studies than those who eat animal based proteins.
"Red meat always comes out top as the worst and that's probably due to its other components.
"But the good news is that there is no evidence that fish is bad for you.
Fish and vegetables best
"So fish plus vegetables is really the best group of proteins."
Dr Longo recommends a diet that is rich in complex carbohydrates and low in protein.
High levels of the growth hormone IGF-I, which is controlled by protein levels, have been linked with cancer.
After the age of about 65 IGF-I levels fall significantly, which can result in muscle loss.
The research found that while high protein intakes raised health risks in the middle-aged it was protective for those over the age of 65.