Higher Quality May Mean Higher Risk

Why is animal protein associated with increased levels of the cancer-promoting growth hormone IGF-1, but not plant protein? Let’s go back to the Tinkertoy analogy. Let’s say you’re trying to build a really big pyramid, and instead of starting from scratch, a pile of little pyramids is dropped in front of you. Ooh, this makes things easier, and you start stacking them together.

But, what if you still want to build your big pyramid, but instead, a pile of cubes were dropped at your feet? You still have all the essential elements there. I mean, you could undo them all, and rebuild them into little pyramids to build into your big pyramid. But you can imagine the cube pile might just not be as good a stimulus as the pyramid pile to instantly just want to start piling them together. Maybe you want see what’s on TV first, or something.

It’s the same thing with our liver and insulin-like growth factor 1. With the exception of the animal protein gelatin, all proteins, plant and animal, contain all nine essential amino acids. So, pretty much all proteins, in that sense, are complete proteins. Other than Jell-O and marshmallows, there’s basically no such thing as incomplete protein. When you hear about high versus low quality proteins, what they’re talking about are the relative proportions of the different essential amino acids. The more closely the proportion matches our own proteins, the higher quality it’s considered.

So, when our liver gets hit with a big load of incoming animal proteins, it’s like, hey, this is easy; let’s just send out IGF-1 to get cells dividing like crazy to use some of this up. It’s like the pile of pyramids. It’s meat; we’re meat, let’s just pile it on.

Whereas when you get plant protein cubes, all the essential elements are there. Your body can break them down into all the essential amino acids it needs, but it just doesn’t stimulate the same kind of real estate boom that animal protein does, so you don’t get as many new cancer condos poppin’ up in your body.

That’s my attempt at a lay explanation; for any biochem geeks out there, basically, unlike the essentials, particularly arginine and the pyruvate precursors may be shunted into gluconeogenesis, oxidized into urea, and so, you know, tend to present less of a proteogenic stimulus, but back to me speaking English.

There’s only one truly “perfect protein.” Without a doubt, the highest quality protein on the planet—for us—is human flesh. Failing that though, any flesh will do. We don’t practice species cannibalism; instead, we practice like kingdom cannibalism, right? Or if fellow mammals, class cannibalism. And by eating other animals, we’re getting protein that more closely mirrors our own than a banana’s—but now, we know that doesn’t necessarily mean it’s a good thing.

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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• Allen NE, Appleby PN, Davey GK, Kaaks R, Rinaldi S, Key TJ. The Associations of Diet with Serum Insulin-like Growth Factor I and Its Main Binding Proteins in 292 Women Meat-Eaters, Vegetarians, and Vegans. Cancer Epidemiol Biomarkers Prev. 2002 Nov;11(11):1441-8.
• Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients). A Report of the Panel on Macronutrients, Subcommittees on Upper Reference Levels of Nutrients and Interpretation and Uses of Dietary Reference Intakes, and the Standing Committee on the Scientific Evaluation of Dietary Reference Intakes. Institute of Medicine. 2005.

Images thanks to: Pearson Scott Foresman, Mikael Häggström, Jwanders, Unused0026, Pengo, Luna04, Stolz, Gary M., and Rex, via Wikimedia Commons; and Karen Schiltz, angelina_koh, and Farm Sanctuary via flickr. Images have been modified.

• animal protein
• arginine
• IGF-1
• meat
• plant protein
• protein