Do high protein diets shorten lifespan?

I’ve written quite a lot on this blog about why a high protein diet is the most effective way to rapidly lose weight and achieve an optimal body composition. I’ve also written about how it’s been shown to prevent fractures and muscle loss in elderly people.

So it comes as a bit of a fly in the ointment when you hear that “ah yes, it may help you lose weight and improve bone density and muscle mass, but it will also cause you to die sooner.”

The claim that a high protein diet shortens lifespan actually comes from the same people who discovered that protein is the central factor controlling appetite and calorie intake, David Raubenheimer and Stephen Simpson at the University of Sydney.

Unfortunately, there is at present no human experimental evidence that can show whether or not a high protein diet has a life shortening effect, so everyone on either side of this debate is forced to rely on experiments in animals. In particular, on mice. Mice, like humans, are omnivores – they generally eat whatever they can get a hold off, and at a fundamental physiological level, they’re quite similar to us. But they’re small and only live two years, which makes big diet experiments feasible.

A decade or so back, Raubenheimer and Simpson conducted a large experiment on mice, in which the mice were randomised to follow diets with varying proportions of protein over the course of their entire life span. In their book “Eat Like the Animals”, they state that this resulted in a dramatic difference in the longevity of the mice. They use the following graph to prove it: