We know excess cellular growth isn’t so good when we’re fully grown adults, since budding tumors may end up being the main beneficiaries of higher levels of circulating growth hormones. But in some circumstances, a little extra growth is sought after, particularly for men in this culture—though not exclusively.

The growth hormone IGF-1 is the reason some dogs look like this, and others like this. What about those who strive to be the big dog? Yes, lower circulating levels of IGF-1 in vegans lowers cancer risk, but might that interfere with their accumulation of muscle mass? There certainly are lots of plant-based body builders, but maybe they’re the exception. To look like this, does one have to risk looking like this?

True or false: Lower IGF-1 levels in vegans likely interferes with muscle accumulation. Is this fact, or is this fiction?

Well, there’s a couple ways you attack that question. For example, what’s the skeletal muscle mass like in acromegaly? People afflicted with giantism—where they have an IGF overload in the body. If IGF bulks up muscle, you’d think they’d be musclebound; but no, they don’t have any more muscle, on average, than anyone else.

What if you inject people with IGF-1? They injected women for a year, and found no increase in lean body mass or grip, bench or leg press strength.

What about men? Basically, same thing. They had about a dozen 22-year-olds flex for 15 weeks under different hormonal milieus, and concluded that elevations in ostensibly anabolic hormones, like IGF-1, with resistance exercise, enhances neither training-induced muscle bulk, nor strength.

“Thus it seems that outside of [genetically engineered mice or a cell culture dish or other animal models] that the search for the true role of the growth potential for IGF-1 in adult muscle hypertrophy is a vain one.” So, although it’s never been directly tested, probably fiction.

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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