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Animal Protein and IGF-1

At first we didn’t know why eating a plant-based diet for just a couple weeks appeared to so dramatically improve cancer defenses. Then, last year, researchers figured it out: eating healthy lowers the level of the cancer promoting growth hormone IGF-1. This saga was detailed in my last four Care2 articles:

What is the mechanism by which a simple dietary change can alter the levels of this cancer promoter? Imagine you’re a kid with some tinker toys. Then for your next birthday you get one of those huge tinker toy sets dumped down in front of you. All excited with this new load of raw building materials, you may really start scaling up. Basically it’s the same with your liver and insulin-like growth factor 1.

When you dump a load of protein in 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.” Thus, your liver starts pumping out IGF-1 to tell all the cells in the body, “it’s growin’ time! Be fruitful and multiply. Spare no expense, go crazy—look how much excess protein we got to work with!”

The problem is that some of the new additions spurred by this growth hormone may be tumors. When you’re a fully-grown adult, cell growth is something we want to slow down—not accelerate. The goal, therefore, would be to maintain adequate, but not excessive, overall protein intake.

Wait a second, though. As I show in my 3-min. video Protein Intake and IGF-1 Production, studies have found no association between total protein intake and IGF-1 levels, but that’s because they didn’t take into account animal versus plant protein. It took a study comparing meat-eaters to vegans to show that higher IGF-1 levels were only associated with animal protein intake. In fact, plant protein seemed to decrease IGF-1 levels. Animal protein appears to send a much different signal to our livers than most plant proteins. Even vegans eating the same amount of protein as meateaters still had lower levels of the IGF-1, so it’s apparently not about excessive protein in general, but about animal protein in particular. To understand why, see the above video pick.

For those who haven’t been following along, see IGF-1 as One-Stop Cancer Shop for the reason we’re so concerned about IGF-1 levels and my videos The Answer to the Pritikin Puzzle and How Plant-Based to Lower IGF-1? to learn about the role diet plays in cancer development. If the reason animal proteins raise IGF-1 levels is because they resemble our own proteins, what about the few plant proteins that just coincidently happen to have amino acid ratios similar to proteins such as soy? Great question! That will be the subject of my Care2 article on Friday.

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my videos for free by clicking here and watch my full 2012 presentation Uprooting the Leading Causes of Death.

Image credit: StuartWebster / Flickr

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Dr. Michael Greger

A founding member of the American College of Lifestyle Medicine, Michael Greger, M.D., is a physician, author, and internationally recognized speaker on nutrition, food safety, and public health issues. Currently Dr. Greger serves as the Director of Public Health and Animal Agriculture at The Humane Society of the United States. Hundreds of his nutrition videos are freely available at


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10:49AM PDT on Jun 19, 2013

Thank you for sharing.

5:18AM PDT on Oct 17, 2012

thanks for sharing :)

11:00AM PDT on Oct 12, 2012

good to know

3:59AM PDT on Oct 12, 2012

Thanks Dr. Greger for the info and the video.

3:41AM PDT on Oct 12, 2012

Interesting :-)

12:45AM PDT on Oct 12, 2012

Thank you. Save your health, save the planet and go vegetarian.

6:46PM PDT on Oct 11, 2012

Love my fruit and veg :-) red papaya is my favourite at the moment :-) yum!!!

4:50PM PDT on Oct 11, 2012

Thanks for the share! :)

2:31PM PDT on Oct 11, 2012

Thank you so much for the single-page article!

7:04AM PDT on Oct 11, 2012

meat-meals are shoved in our faces everywhere! if dining outside its a real challenge to find vegetarian meals.

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