 What is the mechanism by which our diet can affect our levels of this cancer-promoting growth hormone IGF-1? Imagine you're a kid with some tinker toys, then Christmas come early and you get one of those huge sets dumped down in front of you, all excited with this new load of building raw materials you may really start scaling up. And basically it's the same thing with your liver and insulin-like growth factor 1. When you dump a load of protein on your body, your liver's like, whoa, look at all this. What are we going to do with it all? We can't just waste it. We've got to do something with it. Let's just start growing stuff, add a few new additions, maybe a new wing. So your liver decides to start pumping out IGF-1 to tell all the cells in the body it's growing time. Be fruitful and multiply, spare no expense, go crazy. Look how much excess protein we've got to work with. The problem, of course, is that some of the new additions may be tumors. When you're a fully grown adult, cell growth is something we want to slow down, not accelerate. So one might imagine the goal would be to maintain adequate but non-excessive overall protein intake. But wait a second, studies have found no association between total protein intake and IGF-1 levels. Doesn't that just go against everything I just said? Ah, but these studies didn't take into account animal versus plant protein. In this study of meat-eaters, vegetarians, and vegans, they found no significant difference in IGF levels between people eating lots of protein compared to people eating less protein. But before ditching the theory that excessive protein intake boosts the levels of IGF-1, they decided to break it down into animal protein versus plant protein. Higher IGF-1 levels were just associated with animal protein intake. In fact, the plant protein seemed to decrease IGF-1 levels. So no wonder there was no net effect of total protein intake. Animal protein appears to send a much different signal to our livers than most plant proteins. So even those vegans eating the same amount of protein as meat-eaters still had lower levels of the cancer-promoting hormone IGF-1. So it's apparently not about excessive protein in general, but about animal protein in particular. And I'll try to explain why tomorrow.