The Paleo guys will get their pitchforks out: middle-aged Americans with high protein diets are four times more more likely to die of cancer or diabetes than those with diets low in protein.
“As Bad As Smoking”?
That’s according to a new study from the University of Southern California, where researchers looked at thousands of death certificates from people who had participated in the national NHANES nutrition survey.
Those who had died between age 50 to 65 and ate a diet where protein made up 20% or more of daily calories increased the risk of death from cancer or diabetes to the above numbers. In addition, there also was an increased chance of dying prematurely from other causes.
That would put the mortality risk of a high protein diet into the vicinity of smoking cigarettes. Their words, not mine.
The USC guys say that the reason for all this lies in your level of growth hormone IGF-1, which has a molecular structure similar to insulin (IGF-1 = “insulin-like growth factor-1”). When you are young, you need a high IGF-1 level to support growth, and protein keeps you swimming in it. But when you reach middle age, keeping your IGF-1 this high is apparently asking for disaster.
It’s The Animal Protein
The next bit will have vegetarians and vegans rejoice. According to the paper all this is if you get your protein from animal sources.
Those who ate a lot of protein, but got it from plants (nuts, soy, legumes etc.) had a lower risk of dying from cancer. The general risk of dying prematurely, not counting pianos dropping on your head, was gone.
66 Or Older? Get More Protein!
For those 66 or older it didn’t matter whether the protein was plant- or animal-based. As long as people in that age bracket got a diet high in protein, they were about 60% less likely to die of cancer. The general mortality risk was 28% lower.
Why? A study on mice published in the same edition of Cell Metabolism may have the answer: older mice aren’t as good at absorbing protein. If you feed them more protein than they need, they can only process part of it, but end up with a level high enough to have them maintain or increase their weight. That keeps them from becoming frail and needing tiny little walking sticks.
It Ain’t The Last Word
Those on a moral crusade of course take all this as a welcome addition to their arsenal, but to me open questions remain.
Was the higher mortality rate really due to IGF-1, or did those people have a rather one-sided nutrition? The higher IGF-1 may have been coincidence. If it is the guilty party, which one of its mechanisms goes astray? And what exactly happens between age 50 to 65?
Picture courtesy of David Leo Veksler.