If animal proteins are bad because they boost our blood levels of the cancer promoter IGF-1, what about the few plant proteins that just coincidently happen to have amino acid ratios similar to animal proteins—like soy?

One of soy’s selling points is that it has “high quality” protein. But now, we know that from a cancer perspective, higher quality may mean a higher quantity of cancer risk, thanks to IGF-1.

Let’s go back to this study. Those who ate a lot of animal protein had significantly higher levels of IGF-1. And those who ate a lot of non-soy plant protein had significantly lower levels, presumably because it substituted for some of the animal protein in their diets. The same thing might have happened a little with soy—hey, at least you’re not eating animal protein, but this was not a significant decrease.

Meaning if all we do is just swap out animal protein and swap in soy protein, we may not see that beautiful drop in IGF-1 enjoyed by those replacing animal protein instead with a variety of different plant proteins.

Indeed, the more soy milk, for example, that vegan women drank, the higher their IGF levels tended to be. But the trend was only of borderline statistical significance—meaning it could have just been due to chance. To test this once and for all would require the combined might of both the Ornish and Pritikin research teams—a study we’ll cover tomorrow.

To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Kerry Skinner.

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